tag:theconversation.com,2011:/au/topics/vision-1980/articlesVision – The Conversation2024-03-20T12:20:42Ztag:theconversation.com,2011:article/2150432024-03-20T12:20:42Z2024-03-20T12:20:42ZAre you one of the millions about to have cataract surgery? Here’s what ophthalmologists say you need to know<figure><img src="https://images.theconversation.com/files/557920/original/file-20231107-25-sofdb9.jpg?ixlib=rb-1.1.0&rect=60%2C0%2C6720%2C4406&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Cataract surgery removes the clouded lens of the eye and replaces it with a new, clear lens.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/laser-correction-vision-concept-royalty-free-image/1279156312?phrase=cataract%2Bsurgery">Ivan-balvan/iStock via Getty Images Plus</a></span></figcaption></figure><p>Cataract surgery is one of the most popular and commonly performed procedures in the world. The vast majority of patients have excellent outcomes with few complications.</p>
<p>Here are the numbers: </p>
<ul>
<li><p>By age 80, <a href="https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/cataracts">over half of all Americans have cataracts</a>.</p></li>
<li><p>Close to 4 million cataract surgeries are <a href="https://doi.org/10.1136/bmjophth-2020-000464">performed in the U.S. every year</a>.</p></li>
<li><p>Over 90% of patients have <a href="https://doi.org/10.4103/ijo.IJO_1073_22">20/20 vision with glasses after surgery</a>, although those with other eye conditions may not do as well, including those with <a href="https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/glaucoma">glaucoma</a>, a progressive disease typically associated with elevated pressure within the eye; <a href="https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/diabetic-retinopathy">diabetic retinopathy</a>, which ultimately can cause leakage in the retinal tissues; and <a href="https://www.hopkinsmedicine.org/health/conditions-and-diseases/agerelated-macular-degeneration-amd#">macular degeneration</a>, a disease that is typically related to age.</p></li>
<li><p>The <a href="https://www.ncbi.nlm.nih.gov/books/NBK559079/#">rate of post-surgery infection from endophthalmitis</a> is less than 0.1%.</p></li>
</ul>
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<p><a href="https://eye.ufl.edu/profile/steigleman-walter/">As ophthalmologists who have</a> <a href="https://integrity-eye.com/elizabeth-hofmeister/">performed thousands of these procedures</a>, we know that many patients have misconceptions about both cataracts and the surgery. For example, some think a cataract is a growth on the eye’s surface. </p>
<p>We like to compare a cataract with the frosted glass of a bathroom window, where light can be transmitted but details cannot. Or when turbulence from a storm causes normally clear water in the ocean to become murky. In much the same way, the eye’s once transparent lens becomes cloudy. </p>
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<figcaption><span class="caption">After surgery, there’s no bending, inversions, lifting or straining, high-impact activities or eye makeup for one to two weeks or until the doctor says it’s OK.</span></figcaption>
</figure>
<h2>About the surgery</h2>
<p>Cataract surgery removes the clouded lens of the eye and replaces it with a new, clear lens to restore your vision. Most patients report the procedure is painless. </p>
<p>It’s <a href="https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/cataracts/cataract-surgery#">typically an elective surgery</a> that is performed on an outpatient basis. The patient is often awake, under local anesthesia, with sedation similar to that used for dental procedures. We like to say patients receive the equivalent of three margaritas in their IV. </p>
<p>Numbing drops are then applied to the eye’s surface, along with an anesthetic inside the eye. Patients with claustrophobia, or movement disorders such as Parkinson’s disease, may not be suitable candidates for awake surgeries and require general anesthesia.</p>
<p>Before surgery, patients receive dilating drops to make the pupil as large as possible. The surgeon makes a tiny incision, usually with a small pointed scalpel, between the clear and white part of the eye to gain access to the <a href="https://www.aao.org/eye-health/anatomy/lens-capsule-definition">lens capsule</a>, a thin membrane similar in thickness to a plastic produce bag at the grocery store. </p>
<p>This capsule is <a href="https://webvision.med.utah.edu/2020/09/ciliary-zonules/#">suspended by small fibers called zonules</a>, which are arranged like the springs that suspend a trampoline from a frame. The surgeon then creates a small opening in the capsule, called a capsulotomy, to gain access to the cataract. The cataract is then broken into smaller parts so they are removable through the small incision. </p>
<p>This is similar to a tiny jackhammer, breaking the large lens into smaller pieces for removal. That sounds scary, but it’s painless. Ultrasound emulsifies the lens and vacuum power then aspirates it from the eye. </p>
<p>Laser-assisted cataract surgery <a href="https://doi.org/10.3310/hta25060">has been found to have similar outcomes</a> to traditional cataract surgery. </p>
<h2>Complications are rare</h2>
<p>Serious complications, such as postoperative infection, bleeding in the eye or a postoperative retinal detachment are rare; they occur in approximately 1 in 1,000 cases. But even in many of these situations, appropriate management <a href="https://doi.org/10.1038/eye.2015.3">can salvage useful vision</a>. </p>
<p>Capsular complications deserve additional discussion. According to some studies, they occur <a href="https://doi.org/10.1159/000528657">in up to 2% of cases</a>. If a hole or tear of the posterior capsule is encountered during cataract surgery, the clear gel in <a href="https://www.aao.org/eye-health/anatomy/vitreous">the vitreous</a> – the back chamber of the eye – may be displaced into the front chamber of the eye. </p>
<p>If that happens, the gel must be removed at the time of the cataract surgery. This will reduce the likelihood of additional postoperative complications, but those who have the procedure, <a href="https://www.aao.org/eye-health/treatments/what-is-vitrectomy">known as a vitrectomy</a>, have an increased risk for additional complications, including postoperative infections and postoperative swelling. </p>
<h2>After the surgery</h2>
<p>Patients usually go home right after the procedure. Most surgery centers require that the patient have someone drive them home, more for the anesthesia rather than the surgery. Patients begin applying postoperative drops that same day and must wear an eye shield at bedtime for a few weeks after surgery. </p>
<p>Patients should keep the eye clean and avoid exposure to dust, debris and water. They should try not to bend over and should avoid heavy lifting or straining in the first week or so after surgery. Lifting or straining can cause a surge of blood pressure to the face and eye. <a href="https://doi.org/10.1159/000533937">Known as a choroidal hemorrhage</a>, it can lead to bleeding into the wall of the eye and be devastating to vision. </p>
<p>Things that cause only moderate increases in heart rate such as walking are OK. Routine postoperative examinations are usually completed the day after surgery, about a week after surgery and about a month after surgery. </p>
<figure>
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<figcaption><span class="caption">Light and UV exposure, coupled with time, causes the lens of the eye to become increasingly cloudy.</span></figcaption>
</figure>
<h2>A choice of lens</h2>
<p>The plastic lens used to replace the cataract, or <a href="https://www.aao.org/eye-health/diseases/cataracts-iol-implants">intraocular lens</a>, requires careful sizing for optimal results and a nuanced discussion between patient and surgeon. </p>
<p>Early intraocular lens technologies <a href="https://www.ncbi.nlm.nih.gov/books/NBK580484/">were monofocal</a>, and most patients with these lenses chose distance correction and used reading glasses for near tasks. This is <a href="https://www.aao.org/eye-health/diseases/cataracts-iol-implants#">still the preferred approach</a> for approximately 90% of patients having cataract surgery today. </p>
<p>Recent advances have led to <a href="https://www.verywellhealth.com/intraocular-contact-lenses-3421653">intraocular lenses that offer multifocality</a> – the opportunity to have near as well as distance vision, without glasses. Some multifocal lenses are even in the trifocal category, which includes distance, near, and intermediate vision, the latter of which in recent years has become very important for computer and phone use. </p>
<p>Most patients with these advanced technology multifocal lenses <a href="https://doi.org/10.2147/OPTH.S347382">are happy with them</a>. However, a small percentage of patients with multifocal lenses can be so bothered by visual disturbances – notably night glare and halos around light sources in the dark – that they request removal of the multifocal lens to exchange it for a standard intraocular lens. These exchanges are a reasonable option for such situations and offer relief for most affected patients. </p>
<p>Determining who’s an ideal candidate for a multifocal intraocular lens is an area of active research. Most clinicians would recommend against such a lens for a patient with a detail-oriented personality. Such patients tend to <a href="https://doi.org/10.1177/11206721231176313">fixate on the shortcomings of these lenses</a> despite their potential advantages.</p>
<p>As with many technologies, current generation advanced technology intraocular lenses are much better than their predecessors. Future offerings are likely to offer improved vision and fewer side effects than those available today.</p>
<p>But these newer lenses are often not reimbursed by insurance companies and often entail <a href="https://www.bettervisionguide.com/multifocal-iols/">substantial out-of-pocket costs</a> for patients. </p>
<p>Deciding on what type of lens is best for you can be complicated. Fortunately, except in unusual circumstances, such as when a cataract develops after trauma to the eye, there is seldom a hurry for adult cataract surgery.</p><img src="https://counter.theconversation.com/content/215043/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Typically, cataract surgeries are painless and significantly restore vision.Allan Steigleman, Associate Professor of Ophthalmology, University of FloridaElizabeth M. Hofmeister, Associate Professor of Surgery, Uniformed Services University of the Health SciencesLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2213812024-03-12T17:44:46Z2024-03-12T17:44:46ZTotal solar eclipses, while stunning, can damage your eyes if viewed without the right protection<figure><img src="https://images.theconversation.com/files/580528/original/file-20240307-30-bxdz7t.jpg?ixlib=rb-1.1.0&rect=47%2C6%2C4468%2C2383&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Solar eclipses don't come around often, but make sure to view these rare events with eclipse glasses to protect your vision. </span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/USEclipseSchools/0f2e25e7620440c0be042b6516d1acde/photo?Query=eclipse%20viewing&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=524&digitizationType=Digitized&currentItemNo=18&vs=true&vs=true">AP Photo/Charlie Riedel</a></span></figcaption></figure><p>On April 8, 2024, and for the second time in the past decade, people in the U.S. will have an opportunity to <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/">view a total solar eclipse</a>. But to do so safely, you’ll need to <a href="https://preventblindness.org/get-ready-for-the-next-eclipse/">wear proper protection</a>, or risk eye damage.</p>
<p>Earth is the only planet in our solar system where <a href="https://theconversation.com/when-the-sun-goes-dark-5-questions-answered-about-the-solar-eclipse-81308">solar eclipses can occur</a>. During these celestial events, the Moon passes between our planet and the Sun, blocking the Sun and casting a shadow over the Earth. Total eclipses rarely happen multiple times in the same region of a country during one’s lifetime. </p>
<p>The path of totality for <a href="https://science.nasa.gov/eclipses/">this spring’s eclipse</a>, where you can view the total eclipse, will extend over a 100-mile path that crosses through Mexico, Texas, New England and eastern Canada.</p>
<figure>
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<figcaption><span class="caption">Those in the path of totality will have the opportunity to see a total solar eclipse this April.</span></figcaption>
</figure>
<p>As excitement for the celestial show grows across the country, <a href="https://www.forbes.com/sites/jamiecartereurope/2024/03/09/11-ways-to-find-your-last-minute-hotel-for-the-total-solar-eclipse---but-be-quick/?sh=415b5585f4e2">hotels in the path of totality</a> have been booked up by eclipse enthusiasts. Museums and schools have <a href="https://solarsystem.nasa.gov/embeddable-eclipse-events/">planned viewing events</a>, and researchers have developed technology for the <a href="https://astrolab.fas.harvard.edu/LightSound.html">visually impaired and those with hearing loss</a> so more people have the opportunity to experience the eclipse.</p>
<p>Seeing an eclipse is a rare and special opportunity, but <a href="https://directory.hsc.wvu.edu/Profile/28506">as an ophthalmologist</a>, I know that looking directly at the Sun, even for a few moments, can severely damage your eyes. With a few easy precautions, eclipse viewers can protect themselves from severe and irreparable eye damage and vision loss.</p>
<h2>Safe eclipse viewing</h2>
<p>This year’s eclipse will unfold over a 75-minute period, from the moment the Moon starts to partially block the Sun until it completely moves away from it again. </p>
<p>During the partial eclipse period, when the Moon is partly blocking the Sun, you should never look directly at the Sun nor through binoculars, <a href="https://www.masterclass.com/articles/how-to-photograph-a-solar-eclipse">cameras</a> or <a href="https://www.space.com/how-to-photograph-a-solar-eclipse-with-a-smartphone">cellphones</a>. Sunglasses, photographic filters, exposed color film and welding glasses will dim the sunlight, but these items do not prevent <a href="https://www.aao.org/eye-health/tips-prevention/solar-eclipse-eye-safety">eye damage from the Sun’s very intense light rays</a>. </p>
<p>Only <a href="https://preventblindness.org/solar-eclipse-glasses/">solar eclipse glasses</a> with filters designed specifically for observing the partial eclipse are safe to use. They are easily available <a href="https://www.cnn.com/cnn-underscored/outdoors/best-solar-eclipse-glasses?cid=ios_app">from a variety of sources</a>, and you can wear them by themselves or over your glasses or contact lenses. </p>
<p>Keep in mind that these safety filters will permit you to view only the eclipse, as they blacken out everything around you but the Sun itself. Before purchasing a pair, make sure your eclipse glasses are approved by the <a href="https://eclipse.aas.org/eye-safety/iso-certification">ISO 12312-2 international standard</a>.</p>
<p>Only during its <a href="https://eclipse.gsfc.nasa.gov/SEhelp/SEglossary.html">period of totality</a>, the time when the Sun is fully behind the Moon, is it safe to remove your filtered glasses – and then only with caution.</p>
<p>This year, totality will last an unusually long <a href="https://science.nasa.gov/eclipses/future-eclipses/eclipse-2024/">four and a half minutes</a>. If you leave your eclipse glasses on, you will miss seeing the Sun’s bright ring, or corona, behind the Moon. But then, as the Moon moves on, the sky will brighten and you’ll need to put the eclipse glasses back on.</p>
<h2>Eyes and light</h2>
<p>While the pupils of our eyes naturally constrict to limit bright light, and our eyes have pigments to absorb light, direct sunlight overwhelms these functions. Even viewing the Sun for a few brief moments <a href="https://theconversation.com/turn-around-bright-eyes-heres-how-to-see-the-eclipse-and-protect-your-vision-203571">can cause permanent vision loss</a>. </p>
<p>The Sun emits intense <a href="https://www.britannica.com/science/sunlight-solar-radiation">ultraviolet and infrared light</a>, which, while not visible to the human eye, can burn sensitive ocular tissues, such as the cornea and retina.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram of an eye as viewed from the side." src="https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=486&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=486&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=486&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=611&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=611&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581353/original/file-20240312-24-e55u1i.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=611&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The cornea is the clear front surface of the eye, which lets light in. The retina is the inner lining of the back part of the eye, which sends signals to your brain, allowing you to see.</span>
<span class="attribution"><a class="source" href="https://aapos.org/glossary/how-to-safely-view-a-solar-eclipse">American Association for Pediatric Ophthalmology and Strabismus</a></span>
</figcaption>
</figure>
<p>Corneal damage from sunlight, called <a href="https://www.mayoclinic.org/diseases-conditions/actinic-keratosis/symptoms-causes/syc-20354969">solar keratosis</a>, can blur vision and be quite painful. While the cornea can heal itself, it may require several days to get better and lead to lost time at work or school. </p>
<p>Retinal damage, called <a href="https://www.health.wa.gov.au/Articles/S_T/Solar-retinopathy">solar retinopathy</a>, occurs inside the eye. While it isn’t painful, it can be more severe than corneal damage and can dramatically impair vision. Solar retinopathy symptoms include a blind spot in one’s central vision, visual distortions and altered color vision. </p>
<p>In mild cases, these symptoms may go away, but in more severe cases, and even with treatment, <a href="https://aapos.org/glossary/how-to-safely-view-a-solar-eclipse">they may become permanent</a>. </p>
<p>To both enjoy the eclipse and prevent eye damage, make sure you and your loved ones all view the event with strict proper precautions.</p><img src="https://counter.theconversation.com/content/221381/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Geoffrey Bradford does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Now’s the time to get your hands on a pair of eclipse glasses in preparation for April’s display of celestial wonder.Geoffrey Bradford, Professor of Pediatrics and Ophthalmology, West Virginia UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2132002024-03-05T13:59:52Z2024-03-05T13:59:52ZRobber flies track their beetle prey using tiny microbursts of movement<figure><img src="https://images.theconversation.com/files/553851/original/file-20231015-26-ku2y0f.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Robber flies visually track their prey before spearing it with their proboscis.</span> <span class="attribution"><span class="source">Paloma Gonzalez-Bellido</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>April in the Florida Panhandle. It was hot, humid, and a thunderstorm was lurking. But as a fresh graduate student, I was relieved for the escape from my first brutal Minnesota winter. I was accompanying my adviser, <a href="https://scholar.google.com/citations?user=OpaFwzoAAAAJ&hl=en&oi=ao">Paloma Gonzalez-Bellido</a>, on a project that would end up dominating <a href="https://scholar.google.com/citations?user=oux0RxAAAAAJ&hl=en">my Ph.D. work</a>. Out in the scrubland, my eyes darted at every movement, on the alert for an insect that likes shiny beads. </p>
<p><a href="https://doi.org/10.1093/aesa/43.2.227"><em>Laphria saffrana</em></a>, also known as robber flies, are chunky black and yellow flies. Most of a laphria’s head is made up of its large eyes, between which sits a formidable proboscis – a long, tubular mouthpart that can deliver a potent venom capable of incapacitating prey in a heartbeat.</p>
<p>The photos Paloma showed me before we got there, though stunning, were of no help in looking for the fly. There were insects flying in every direction, their movements a blur, making it impossible to pick out any details. I only had a split second to figure out whether the thing I was seeing was a laphria, a similarly colored yellowjacket wasp, or something else entirely. </p>
<p>Despite their <a href="https://doi.org/10.1016/j.cub.2017.02.032">relatively crude vision</a>, the flies I was looking for are far more adept than I am at picking out the insects they’re targeting. Somehow they’re able to zero in on their prey of choice: beetles. Based on her field observations the previous year, Paloma thought they did this by looking for the flash of beetle wings.</p>
<p>If she was right, laphria have hit upon an ingenious trick that balances the need for speed, accuracy and specificity. Here are some of the clues we’ve found to <a href="https://doi.org/10.1016/j.cub.2023.06.019">the secrets of their success</a>. </p>
<h2>Following the flash</h2>
<p>Paloma had previously studied other predator insects such as dragonflies and killer flies. Their <a href="https://www.sciencedirect.com/topics/medicine-and-dentistry/compound-eye">compound eyes</a> don’t provide a lot of detail about the visual world, making it possible to trick them into chasing simple beads as if they were their prey insects.</p>
<p>But when Paloma tried the same sleight of hand on laphria, they wouldn’t go for the regular black beads. They chased only clear beads. </p>
<p>The one important difference between laphria and the other predators Paloma had studied is that they’re picky eaters. Their prey of choice are beetles. So, Paloma and our collaborator, Jennifer Talley, speculated that the reason laphria are attracted to shiny beads is because they reflected light and flashed like the clear wings of a beetle.</p>
<p>In Florida, we tested this idea by swapping out the plain black beads for a panel of LED lights that we could program to flash in sequence at a frequency that matched the wing beats of beetles, which can be anywhere from 80 to 120 beats per second. </p>
<figure>
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<figcaption><span class="caption">The experimental setup, with a robber fly sitting on a log facing the LED light panel.</span></figcaption>
</figure>
<p>In an outdoor enclosure, Paloma placed previously caught robber flies one after the other on a log. Outside, Jennifer and I controlled the LED panel in front of the log and the high-speed cameras that captured the action.</p>
<p>The LED pixels flashed in sequence, simulating a moving target. Laphria tracked the lights with keen interest only when they flashed at the same frequency at which beetles flapped their wings.</p>
<p>But even as our initial experiments began confirming the hypothesis, a new puzzle presented itself. How do the flies accurately track their prey?</p>
<h2>Unique strategy to track and identify</h2>
<p>Before they give chase, all visual predators, including laphria, need to accurately track their prey’s movements. Although many animals have this ability, what we found in laphria was, to our surprise, a slightly tweaked formula compared with other predators. Their strategy allows them not only to accurately track but also count those flashes from their prey’s wing movements.</p>
<p>When I looked at the high-speed videos of laphria tracking the flashing LEDs and actual beetles, I noticed that they primarily moved their head in short bursts, called <a href="https://eyewiki.aao.org/Saccade">saccades</a>, interspersed with little or no other movements. These saccades are extremely quick, lasting less than 40 milliseconds, and the time between them is only slightly longer. To the naked eye, this looks like continuous motion, but our high-speed videos show otherwise. The degree to which the flies moved their heads during each burst depended on the speed of the target and how far off center it was from the direction of the fly’s gaze.</p>
<figure>
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<figcaption><span class="caption">Watch a robber fly watching moving lights it perceives as a prey beetle.</span></figcaption>
</figure>
<p><a href="https://doi.org/10.1016/j.cub.2023.06.019">What our findings told us</a> is that instead of continuously moving their heads to maintain the position of the target within the most sensitive parts of their eyes, laphria allow it to pass over their retina, moving only when it slips out of focus. We think this strategy helps them count the flashes of the prey’s beating wings, which determines their continued interest.</p>
<p>That is, the laphria know the wingbeat frequency of their most tasty prey and so pay attention to flashes that match. If the flash count matches their expectations, they will continue to track the target after it slips out of the sensitive zone of their eyes.</p>
<p>To bring it back into focus, though, they have to account for its speed and the position where they last saw it. Because the size of the saccade matches the speed of the prey, we think the laphria are keeping track of how fast the prey moves while at the same time counting the flashes from its wingbeats. So once a beetle slips out of focus, the predator knows how much to move its head to refocus.</p>
<p>Even though people track moving objects all the time – like while playing sports such as baseball or tennis or even just while watching a bird fly by – <a href="https://www.freethink.com/series/the-edge/eye-tracking">it’s a complex process</a>. It involves dynamic cross-talk between the visual and muscular systems.</p>
<p>Regardless of the motivation, the goal while visually tracking a target is the same – to train the most sensitive zone of the eyes, <a href="https://www.ncbi.nlm.nih.gov/books/NBK554706/">known as the fovea</a>, onto the item of interest. <em>Laphria saffrana</em> have seemingly tweaked that rule so they can learn more about the target. Their customized prediction strategy allows them to accurately locate and quickly chase down their very specific dietary needs.</p><img src="https://counter.theconversation.com/content/213200/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Siddhant Pusdekar does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Not much is known about the predator fly Laphria saffrana. New research identified how they count the wingbeats of their favored prey, letting it slip out of focus before adjusting their heads.Siddhant Pusdekar, Graduate Researcher in Ecology, Evolution and Behavior, University of MinnesotaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2217862024-01-25T16:08:19Z2024-01-25T16:08:19ZAnimals see the world in different colours than humans – new camera reveals what this looks like<figure><img src="https://images.theconversation.com/files/571226/original/file-20240124-17-mpvmh4.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C644%2C644&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Visualising the colours birds perceive reveals the ultraviolet patterns that are usually hidden from us.</span> <span class="attribution"><a class="source" href="https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3002444#sec014">Vasas et al. (2024) PLOS Biology</a>, <span class="license">Author provided</span></span></figcaption></figure><p>If you’ve ever wished you could see the world though the eyes of another animal, we have good news for you. We also wondered about that and, being scientists who specialise in colour vision, have created a solution: a camera system and software package that allows you to record videos <a href="http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3002444">in animal-view colours</a>.</p>
<p>Many animals, including bees, birds and <a href="https://www.sciencefriday.com/articles/ultraviolet-light-animals/#:%7E:text=Okay%2C%20fine%2C%20mammals%20can%20have,with%20their%20short%20blue%20cones.">even mammals</a> like reindeer and mice can perceive ultraviolet light. Indeed, the lack of UV-sensitivity in humans is more of an exception than the rule. At the other end of the visible light spectrum, human eyes have receptors that are sensitive to red while many animals – including bees, mice and dogs – are just as blind to red as we are to ultraviolet light. </p>
<p>Even when it comes to blues and greens, colours perceived across the animal kingdom, the precise wavelength of the light an animal would experience as “pure blue” or “pure green” is specific to the species. As a result, no two species see the world in the same colours.</p>
<p>We invite you to stare at the sky and appreciate that its blueness is the joint product of the sunlight being scattered in the atmosphere and your own sensory system. The colour you see is specific to you – in fact, for many animals, the sky is ultraviolet-coloured.</p>
<p>Now, slowly lower your eyes and try to imagine how the rest of the landscape could appear for other species. With our new camera system, we took one step closer to understanding this wonderful, strange world that other animals live in.</p>
<h2>Capturing the world in motion</h2>
<p>While we cannot possibly imagine how ultraviolet appears to the animals who can perceive it, we can visualise it using false colour imagery. For example, for honeybees that are sensitive to three types of light (ultraviolet, blue and green), we can shift their perceivable colours into the human visible range such that ultraviolet is represented as blue, blue becomes green, and green becomes red.</p>
<p>Up until now, we could only apply this process to immobile objects. False colour photography relies on taking a series of photos through a succession of optic filters and subsequently overlaying them, and this sequential method means that everything must be in the exact same position in all the photos.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/571229/original/file-20240124-23-rt4qn2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A large butterfly in fluorescent orange and purple hues contrasted with a smaller yellow version of the same image." src="https://images.theconversation.com/files/571229/original/file-20240124-23-rt4qn2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/571229/original/file-20240124-23-rt4qn2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/571229/original/file-20240124-23-rt4qn2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/571229/original/file-20240124-23-rt4qn2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/571229/original/file-20240124-23-rt4qn2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/571229/original/file-20240124-23-rt4qn2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/571229/original/file-20240124-23-rt4qn2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A museum specimen of <em>Phoebis philea</em> seen using false colour imaging.</span>
<span class="attribution"><a class="source" href="https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3002444#sec014">Vasas et al. (2024) PLOS Biology</a></span>
</figcaption>
</figure>
<p>This is a serious drawback. It makes for a laborious process which sets the limit on the number of objects that can be realistically imaged. For example, taking photos of an iridescent peacock feather from a hundred different angles would require screwing on and off each filter a hundred times.</p>
<p>Even worse, all movement-related information is discarded. Yet the living world is in constant motion: trees sway in the wind, leaves flutter, birds hop along branches looking for insects that scutter in the undergrowth. We needed a way to be able to visualise all this movement.</p>
<p>The first challenge was to devise a camera that records in ultraviolet and visible light simultaneously. The solution turned out to be a beam splitter. This specialised piece of optical equipment reflects ultraviolet light as if it was a mirror, but allows visible light to pass through, just like clear glass. </p>
<p>We positioned two cameras (nothing too fancy, the same kind you can buy in shops and online, but with one modified to record in ultraviolet) in a 3D-printed casing, such that the modified camera received reflected ultraviolet light while a stock camera received transmitted visible light. We overlayed and synchronised the recordings of these two cameras, and a series of conversion steps allowed us to calculate the amount of light that had reached each camera’s sensors. </p>
<p>From this, we could estimate the amount of light that would have been captured by an animal’s eye if it were seeing the scene from the vantage point of our camera.</p>
<iframe src="https://widgets.figshare.com/articles/25049583/embed?show_title=1" width="100%" height="351" allowfullscreen="" frameborder="0"></iframe>
<h2>Try it yourself</h2>
<p>We have made all <a href="https://github.com/hanleycolorlab/video2vision">codes</a> necessary for implementing the video conversions and the <a href="https://gitlab.com/multispectrum-beamsplitter">plans</a> of the camera system freely available online, along with our best attempt to explain how to build the camera from scratch. </p>
<p>Our goal is for other researchers to build their own cameras and to use them to answer their own questions about how other species see the world. There are so many possibilities. </p>
<p>We can record the dances of peacocks and see how dazzling their feathers appear to peahens. The iridescence of these feathers extends into the ultraviolet – our recordings show the feathers appear even more colourful for their target audience than to us.</p>
<p>We can accurately describe how the startle displays of caterpillars appear to their bird predators, and understand why the unexpected flash of colourful patterns scares them away. We can ask questions about how animals move between spots on the forest floor to show off or hide their colours. </p>
<p>We can also create image records of butterflies and other insects held in museum collections and offer animal-view conversions as part of a digital library. And we can ensure glass facades are sufficiently visible to birds who might <a href="https://theconversation.com/billions-of-birds-collide-with-glass-buildings-but-architecture-has-solutions-215419">otherwise collide with them</a>.</p>
<p>But the most exciting questions will be those we have yet to consider. Only now that we have started taking videos of the natural world in colours that animals see are we beginning to notice how much information is out there. Discoveries await you in your own backyard.</p>
<hr>
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<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><strong><em>Don’t have time to read about climate change as much as you’d like?</em></strong>
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<hr><img src="https://counter.theconversation.com/content/221786/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Daniel Hanley received funding from the National Geographic Society.</span></em></p><p class="fine-print"><em><span>Vera Vasas does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Humans can’t see ultraviolet light – but lots of other animals can.Vera Vasas, Research Fellow in Ecology and Evolution, University of SussexDaniel Hanley, Assistant Professor, George Mason UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2197702024-01-19T16:54:18Z2024-01-19T16:54:18ZWhy the 20-metre number plate eyesight test isn’t fair<figure><img src="https://images.theconversation.com/files/570096/original/file-20240118-27-tw3spq.jpg?ixlib=rb-1.1.0&rect=15%2C0%2C5301%2C3547&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/many-cars-on-road-top-view-2296151421">Kichigin/Shutterstock</a></span></figcaption></figure><p><a href="https://www.gov.uk/government/news/under-50-of-motorists-aware-they-must-read-a-number-plate-from-20-metres-figures-show">Less than half</a> of UK motorists surveyed by the Driver and Vehicle Licensing Agency (DVLA) know they must be able to read a number plate from 20 metres away in order to drive safely. </p>
<p>As a vision test, it’s quick and easy. It’s not difficult to find a number plate to conduct the eyesight test and the DVLA gives suggestions for approximating 20m - five car lengths or the width of eight parking bays. But is it a fair test of vision for driving?</p>
<p>As a rough and ready test, it’s easy to administer when you wouldn’t otherwise have a vision test to hand. However, there are significant variables: the amount of light, time of day, weather conditions, the person’s age, the colour and cleanliness of the number plate, and the actual letters and spacing, can make significant differences to how easy it is to read.</p>
<p>In UK ophthalmology clinics, visual acuity is measured and reported as a fraction, such as 6/6, 6/9 or 6/12 on the <a href="https://en.wikipedia.org/wiki/Snellen_chart">Snellen test</a>. The numerator (number above the line) is the distance of the eye from the Snellen chart (in metres) and the denominator corresponds to the line of the letter chart. The largest letter on the chart usually represents 6/60 Snellen acuity. The smaller the denominator, the better the vision; the larger the denominator, the poorer the vision.</p>
<p>The test was created by the Dutch physician Hermann Snellen in the 1860s and is slowly being replaced by a newer test called <a href="https://www.youtube.com/watch?v=ByRMrL7iwpE">LogMAR</a>, which has more equal letter spacing. But, for now, driving requirements in the UK remain in Snellen. </p>
<p>People are pretty familiar with the term 20/20 vision, which is used to describe a good, clear, level of vision. The term 20/20 comes from the American model of measuring acuity, where the numerator refers to a 20-foot distance. Having 20/20 vision therefore equates to 6/6 vision in the UK on the Snellen chart, with a 6m numerator distance. </p>
<h2>The crowding problem</h2>
<p>To meet driving standards in the UK, you <a href="https://www.gov.uk/driving-eyesight-rules">need to have</a> a minimum 6/12 Snellen vision, a full visual field (the test of your peripheral vision) and also be able to read a number plate at 20m. Some people who meet the Snellen visual acuity and visual field requirements can’t see all of the letters of a number plate at 20m because of a phenomenon called crowding.</p>
<p>Crowding occurs when it is harder to identify a letter surrounded by other letters, than a letter on its own. It’s why the edge letters of the number plate are easier to identify than the middle letters. </p>
<p>There are some conditions in which people experience more crowding than others, such as <a href="https://www.hra.nhs.uk/planning-and-improving-research/application-summaries/research-summaries/the-perceptual-effects-of-crowding-in-amblyopic-and-developing-vision/">amblyopia</a> (lazy eye), <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6361551/">glaucoma</a> (increased pressure inside the eye resulting in nerve damage) and <a href="https://www.nature.com/articles/s41598-017-08652-0#">older age</a>.</p>
<p>Crowding impairs people’s ability to recognise and respond to cluttered objects. It is not well understood, but we know it happens within the visual cortex – the vision processing part of the brain, because people experience crowding even when image clutter is <a href="https://www.cell.com/current-biology/pdf/S0960-9822(11)00824-4.pdf">presented separately</a> to either eye. </p>
<p>In crowding, the “busier” and more cluttered the visual information being processed in the visual cortex, the more difficult the image segregation. It’s not that the objects cannot be seen, it’s that they cannot be effectively separated.</p>
<p>So is it fair or important that we continue to check visual acuity, including crowding with the 20m test? </p>
<p>The UK has an ageing population, working longer to retire and wanting to remain independent. In fact, the DVLA reports that the number of motorists aged 90 or older has <a href="https://www.telegraph.co.uk/news/2024/01/01/old-drivers-nineties-record-dangerous-eye-sight-checks-aa/#:%7E:text=The%20number%20of%20drivers%20aged,from%2077%2C000%20in%20November%202013.">doubled</a> to more than 150,000 over the last decade. </p>
<figure class="align-center ">
<img alt="Older adult man driving a car" src="https://images.theconversation.com/files/570127/original/file-20240118-21-xk277k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/570127/original/file-20240118-21-xk277k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/570127/original/file-20240118-21-xk277k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/570127/original/file-20240118-21-xk277k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/570127/original/file-20240118-21-xk277k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/570127/original/file-20240118-21-xk277k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/570127/original/file-20240118-21-xk277k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The UK has an ageing population that would like to remain independent.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/retired-elder-man-driving-blue-car-113829484">ESB Professional/Shutterstock</a></span>
</figcaption>
</figure>
<p>Visual acuity <a href="https://www.sciencedirect.com/science/article/pii/S0039625715000259?via%3Dihub">shows weak</a>, if any correlation with crash statistics or driving performance. Contrast sensitivity (the ability to differentiate shades of grey) may show <a href="https://www.sciencedirect.com/science/article/pii/S0042698910002531?via%3Dihub">better correlation</a>, yet isn’t tested for driving at all.</p>
<p>A 2008 <a href="https://www.sciencedirect.com/science/article/pii/S0001457508001449?via%3Dihub">study</a> found no reliable differences in crashes and serious accidents between Australian states with and without mandatory age-based fitness-to-drive vision testing. </p>
<p>Glare sensitivity, visual field loss, and useful field of view (the area you can extract visual information from in a single glance without moving your eyes) are <a href="https://iovs.arvojournals.org/article.aspx?articleid=2124993">significant predictors</a> of driving accidents. And the useful field of view has been shown by several studies to play an <a href="https://pubmed.ncbi.nlm.nih.gov/32999975/">important role</a> in a person’s ability to drive safely.<br>
Current driving tests, based primarily on visual acuity, may exclude some safe drivers and miss other important aspects of visual or cognitive impairment that are more directly related to driving ability. </p>
<p>While some might find the lack of legal eyesight requirement to drive a mobility scooter <a href="https://www.gov.uk/mobility-scooters-and-powered-wheelchairs-rules/eyesight-requirements">troubling</a>, the social isolation and depression associated with stopping driving are <a href="https://academic.oup.com/biomedgerontology/article/60/3/399/630618">also concerning</a>.</p>
<p>Our current standards could be eliminating people from driving who would be good drivers according to better test predictors. </p>
<p>But, without a better test at the roadside, is it helpful to use a readily available number plate test – despite its flaws – to give an instant assessment rather than not have anything at all? Or would it be better to direct drivers to a more reliable test, taken within an appropriate time frame? </p>
<p>In an ageing population with increasing retirement ages such as the UK, this may be something we need to think about in the near future.</p><img src="https://counter.theconversation.com/content/219770/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Charlotte Codina does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>There are more reliable tests of visual acuity.Charlotte Codina, Lecturer, Orthoptics, University of SheffieldLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2193782023-12-18T13:23:43Z2023-12-18T13:23:43ZDo you hear what I see? How blindness changes how you process the sound of movement<figure><img src="https://images.theconversation.com/files/565875/original/file-20231214-23-s4v8j4.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2048%2C1462&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Sighted people would have a hard time crossing the street by sound alone.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/full-length-of-blind-woman-crossing-road-with-stick-royalty-free-image/1210268422">Maskot/DigitalVision via Getty Images</a></span></figcaption></figure><p>Almost nothing in the world is still. Toddlers dash across the living room. Cars zip across the street. Motion is one of the most <a href="https://doi.org/10.1088/0954-898X/6/3/003">important features in the environment</a>; the ability to predict the movement of objects in the world is often directly related to survival – whether it’s a gazelle detecting the slow creep of a lion or a driver merging across four lanes of traffic.</p>
<p>Motion is so important that the primate brain evolved a dedicated system for processing visual movement, known as the middle temporal cortex, <a href="https://doi.org/10.1016/B978-0-444-53860-4.00005-2">over 50 million years ago</a>. This region of the brain contains neurons specialized for detecting moving objects. These <a href="https://doi.org/10.1093/acrefore/9780190264086.013.76">motion detectors</a> compute the information needed to track objects as they continuously change their location over time, then sends signals about the moving world to other regions of the brain, such as those involved in planning muscle movements.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/565877/original/file-20231214-21-e83re8.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram of brain with the middle temporal gyrus — a strip on the bottom side of the brain — highlighted in yellow" src="https://images.theconversation.com/files/565877/original/file-20231214-21-e83re8.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/565877/original/file-20231214-21-e83re8.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=347&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565877/original/file-20231214-21-e83re8.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=347&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565877/original/file-20231214-21-e83re8.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=347&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565877/original/file-20231214-21-e83re8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=436&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565877/original/file-20231214-21-e83re8.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=436&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565877/original/file-20231214-21-e83re8.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=436&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The middle temporal cortex is involved in processing visual movement.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Gray726_middle_temporal_gyrus.png">Gray, vectorized by Mysid, colored by was_a_bee/Wikimedia Commons</a></span>
</figcaption>
</figure>
<p>It’s easy to assume that you see and hear motion in a similar way. However, exactly how the brain processes auditory motion has been an <a href="https://doi.org/10.1016/j.brainres.2007.03.003">open scientific question</a> for at least 30 years. This debate centers on two ideas: One supports the existence of specialized auditory motion detectors similar to those found in visual motion, and the other suggests that people hear object motion as discrete snapshots.</p>
<p>As <a href="https://scholar.google.com/citations?user=WtPLYRIAAAAJ&hl=en">computational</a> <a href="https://scholar.google.com/citations?user=5LuGpVgAAAAJ&hl=en">neuroscientists</a>, we became curious when we noticed a blind woman confidently crossing a busy intersection. <a href="https://faculty.washington.edu/ionefine/">Our laboratory</a> has spent the past 20 years examining where auditory motion is represented in the brains of blind individuals.</p>
<p>For sighted people, crossing a busy street based on hearing alone is an impossible task, because their brains are used to <a href="https://doi.org/10.1364/JOSAA.20.001391">relying on vision</a> to understand where things are. As anyone who has tried to find a beeping cellphone that’s fallen behind the sofa knows, sighted people have a very limited ability to pinpoint the location or movement of objects based on auditory information.</p>
<p>Yet people who become blind are able to make sense of the moving world using only sound. How do people hear motion, and how is this changed by being blind?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/565879/original/file-20231214-27-s4v8j4.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Aerial view of pedestrians on a crosswalk, a few cars waiting at the edges" src="https://images.theconversation.com/files/565879/original/file-20231214-27-s4v8j4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/565879/original/file-20231214-27-s4v8j4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565879/original/file-20231214-27-s4v8j4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565879/original/file-20231214-27-s4v8j4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565879/original/file-20231214-27-s4v8j4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565879/original/file-20231214-27-s4v8j4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565879/original/file-20231214-27-s4v8j4.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">People who are blind are better able to track auditory motion in noisy conditions compared with sighted people.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/pedestrians-on-zebra-crossing-new-york-city-royalty-free-image/1048763642">Orbon Alija/E+ via Getty Images</a></span>
</figcaption>
</figure>
<h2>Crossing a busy street by sound alone</h2>
<p>In our <a href="https://doi.org/10.1073/pnas.2310156120">recently published study</a> in the journal PNAS, we tackled the question of how blind people hear motion by asking a slightly different version of it: Are blind people better at perceiving auditory motion? And if so, why?</p>
<p>To answer this question, we used a simple task where we asked study participants to judge the direction of a sound that moved left or right. This moving sound was embedded in bursts of stationary background noise resembling radio static that were randomly positioned in space and time.</p>
<p>Our first question was whether blind participants would be better at the task. We measured how loud the auditory motion had to be for participants to be able to perform the task correctly 65% of the time. We found that the hearing of blind participants was no different from that of sighted participants. However, the blind participants were able to determine the direction of the auditory motion at <a href="https://doi.org/10.1073/pnas.2310156120">much quieter levels</a> than sighted participants. In other words, people who became blind early in life are better at hearing the auditory motion of objects within a noisy world. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/565949/original/file-20231215-28-skziw1.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="showing motion of object from one corner of a plane to another, where the blind participant is able to detect the position of the object more closely than the sighted participant" src="https://images.theconversation.com/files/565949/original/file-20231215-28-skziw1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/565949/original/file-20231215-28-skziw1.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565949/original/file-20231215-28-skziw1.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565949/original/file-20231215-28-skziw1.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565949/original/file-20231215-28-skziw1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565949/original/file-20231215-28-skziw1.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565949/original/file-20231215-28-skziw1.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Blind participants were able to determine the position of the object as it starts and stops moving more closely than sighted participants.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1073/pnas.2310156120">Ione Fine and Woon Ju Park</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>We then examined how the noise bursts interfered with the ability to tell the direction of motion. For both sighted and blind participants, only the noise bursts at the beginning and the end of each trial had an effect on performance. These results show that people do not track objects continuously using sound: Instead they infer auditory motion from the <a href="https://doi.org/10.1073/pnas.2310156120">location of sounds at their beginning and end</a>, more consistent with the snapshot hypothesis. </p>
<p>Both blind and sighted people inferred movement from the start and stop of sounds. So why were blind people so much better at understanding auditory motion than sighted people? </p>
<p>Further analysis of the effects of background noise on the ability to track auditory motion showed that blind participants were affected only by noise bursts occurring at the <a href="https://doi.org/10.1073/pnas.2310156120">same locations in space and moments in time</a> as the onset and offset of the moving sound. This means that they were more sensitive to the beginning and end of the actual auditory motion and less susceptible to irrelevant noise bursts.</p>
<h2>When you hear what I see</h2>
<p>As any parent of a blind child will tell you, understanding motion is just <a href="https://nfb.org/our-community/parents-blind-children">one of the many ways</a> that blind children learn to interact with the world using different cues and actions. </p>
<p>A sighted baby recognizes their parent’s face as they approach the crib, while a blind baby recognizes the sound of their footsteps. A sighted toddler looks toward the dog to attract their parent’s attention, while a blind toddler might <a href="https://doi.org/10.1017/S0954579403000142">pull their parent’s hand</a> in the direction of the barking. </p>
<p>Understanding the ability of blind people to <a href="https://doi.org/10.1146/annurev-vision-102016-061241">learn how to successfully interact</a> with a world designed for the sighted provides a unique appreciation of the extraordinary flexibility of the human brain.</p><img src="https://counter.theconversation.com/content/219378/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>This work was supported by NIH National Eye Institute Grants R01EY014645 (to I.F.) </span></em></p><p class="fine-print"><em><span>Woon Ju Park receives funding from an NIH National Eye Institute Grant K99EY034546 and was supported by a Weill Neurohub Postdoctoral Fellowship. </span></em></p>Detecting and tracking motion is key to survival. The ability to extract auditory information from a noisy environment changes when your brain isn’t wired to rely on vision.Ione Fine, Professor of Psychology, University of WashingtonWoon Ju Park, Research Scientist, University of WashingtonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2128332023-09-22T13:15:50Z2023-09-22T13:15:50ZHow ducks, geese and swans see the world – and why this puts them at risk in a changing environment<figure><img src="https://images.theconversation.com/files/547482/original/file-20230911-16-nwvjjz.jpg?ixlib=rb-1.1.0&rect=0%2C200%2C909%2C578&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The blue duck (Hymenolaimus malacorhynchos) is a species endemic to New Zealand.</span> <span class="attribution"><span class="source">Graham Martin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span></figcaption></figure><p>Each year, <a href="https://doi.org/10.1111/j.1474-919X.2011.01117.x">millions of birds</a> fly into power lines, wind turbines and the other man-made structures that litter the open air space. These collisions frequently result in the death of birds and, if power systems go down, disrupt our lives and pose financial challenges for power companies.</p>
<p>Numerous bird species, including <a href="https://doi.org/10.1111/ibi.13139">macaws in Brazil</a>, <a href="https://scholar.google.com/scholar_lookup?title=Landscape+Features+and+Flight+Behaviour+Associated+with+Power+Line+Collision+Risk+for+Swans+and+Geese+in+Northwest+England,+and+an+Assessment+of+Mitigation+Measures+for+Reducing+Risk+Levels&author=Taylor,+C.&author=Hartley,+I.&author=Rees,+E.&publication_year=2015">geese and swans in the UK</a>, and <a href="https://doi.org/10.1111/j.1474-919X.2010.01039.x">blue cranes in South Africa</a> have been found to be susceptible to collisions with power lines. But <a href="https://doi.org/10.1111/j.1474-919X.1994.tb01116.x">any flying bird</a> can fall victim to such a collision. </p>
<p>In some places, these collisions happen so often that they can <a href="https://doi.org/10.1111/ibi.12553">jeopardise local populations</a> of endangered species. </p>
<p>But birds are highly evolved flying machines. They can fly in tightly packed flocks that weave and turn to our delight and wonder. So why do they fly into things?</p>
<p>According to <a href="https://doi.org/10.1098/rspb.2023.1213">our latest research</a>, the answer lies in how they see the world. We found that looking directly ahead is simply not that important to many species of <a href="https://www.rspb.org.uk/birds-and-wildlife/wildlife-guides/bird-a-z/ducks-geese-and-swans/">duck, geese and swans</a>.</p>
<figure class="align-center ">
<img alt="A flock of swans flying past a power line." src="https://images.theconversation.com/files/548362/original/file-20230914-21-77m7k1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548362/original/file-20230914-21-77m7k1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=422&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548362/original/file-20230914-21-77m7k1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=422&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548362/original/file-20230914-21-77m7k1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=422&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548362/original/file-20230914-21-77m7k1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=531&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548362/original/file-20230914-21-77m7k1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=531&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548362/original/file-20230914-21-77m7k1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=531&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Seeing what’s ahead is not that important to many species of duck, geese and swans.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/flock-swans-flying-over-cables-transmission-1723566097">Marijs Jan/Shutterstock</a></span>
</figcaption>
</figure>
<h2>How birds see the world</h2>
<p>Exploring the reasons behind why birds are victims of collisions has led to new ideas that challenge our fundamental perception of what birds are. In the past, scientists have described birds as <a href="https://doi.org/10.1016/j.cub.2022.06.065">“a wing guided by an eye”</a>. This implies that flight has been central to moulding bird vision throughout their evolution.</p>
<p>But now it is safe to conclude that a bird is instead best characterised as “a bill guided by an eye”. Rather than flight, the main driver of the evolution of bird vision has been the key tasks associated with foraging, in particular detecting food items and getting the bill to the right place at the right time in order to seize them. Alongside the detection of predators, this is the task that bird vision has to get right day in, day out.</p>
<p>Birds differ in how much the view from each eye overlaps (called the binocular field of view). The more the eyes look straight ahead, the more the view from each eye will overlap – much as human eyes do – thus broadening the binocular field. For a bird such as a duck, with its eyes positioned high up on either side of the head, the view from each eye will be very different (with smaller binocular field). </p>
<p>We measured binocular field size across a broad range of 39 species of duck, geese and swans. We found that the key driver of diversity in vision between species is their diet and how they forage for food. </p>
<p>Birds that primarily use their vision to locate foods such as seeds, or selectively graze on plants, tend to have broader binocular fields. </p>
<p>However, the binocular fields of species like <a href="https://www.rspb.org.uk/birds-and-wildlife/wildlife-guides/bird-a-z/mallard/">mallards</a> and <a href="https://www.waterfowl.org.uk/wildfowl/swans-geese-allies/pink-eared-duck/">pink-eared ducks</a> <a href="https://doi.org/10.1111/j.1474-919X.2006.00611.x">are much narrower</a>. These birds rely less on their eyes for foraging and more on touch cues from their bills. The vision of birds like these instead provides them with a comprehensive view of the region above and behind their heads.</p>
<p>Birds certainly need to have some visual coverage in front of them. But with eyes placed high on the side of the head, resulting in a very narrow binocular field, they are restricted to retrieving rather scant detail from the distant scene ahead. What matters to them more is placing their bill accurately at a close distance and seeing who is coming at them from the side or from behind.</p>
<figure class="align-center ">
<img alt="Two pink-eared ducks in water." src="https://images.theconversation.com/files/548359/original/file-20230914-8719-q2oh4v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548359/original/file-20230914-8719-q2oh4v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548359/original/file-20230914-8719-q2oh4v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548359/original/file-20230914-8719-q2oh4v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548359/original/file-20230914-8719-q2oh4v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548359/original/file-20230914-8719-q2oh4v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548359/original/file-20230914-8719-q2oh4v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Pink-eared ducks rely less on their eyes for foraging.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/pink-eared-duck-australia-1418556047">Imogen Warren/Shutterstock</a></span>
</figcaption>
</figure>
<p>This finding is not confined to ducks, geese and swans. It probably generalises to all birds, except perhaps some owls (which have more front-facing eyes and rely upon sound to locate prey). The great majority of birds are therefore vulnerable to collisions. </p>
<p>However, it is larger birds like geese, swans and <a href="https://www.britannica.com/animal/bustard">bustards</a> that face real problems. Their restricted forward vision is compounded by flying fast and being unable to change direction quickly. These birds also often fly in flocks, and at dusk and dawn when the light level is lower. </p>
<h2>Warning birds of hazards ahead</h2>
<p>Understanding the vision of birds from the perspective of foraging and predator detection improves our understanding of what causes collisions. But, more importantly, it allows us to do something about it. </p>
<p>We must not assume that a bird’s view of the world is the same as ours. We are specialised primates with eyes on the front of our heads, and we see the world in a <a href="https://link.springer.com/article/10.1007/s10336-011-0771-5">very different way</a> to birds, not only with respect to visual fields but also acuity and colour vision. So, we must try to take a proper “birds’ eye view” of the problem. </p>
<p>Birds are also flying fast. But, as they do so, they are taking in only gross information of what lies ahead – much as we do when driving our cars. As with car hazard warnings, it is necessary to alert birds <a href="https://doi.org/10.1016/j.gecco.2023.e02386">using markers</a> that may seem excessive.</p>
<p>Birds that are vulnerable to collisions have evolved to fly in airspace that only recently has started to become cluttered. To be clearly visible to a bird, especially to species like ducks and geese, <a href="https://doi.org/10.3390/birds3040028">devices that warn birds about hazards ahead</a> must be large, highly contrasting and produce flicker.</p>
<p>When marking hazards, there is no place for subtlety. </p>
<hr>
<figure class="align-right ">
<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
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<p class="fine-print"><em><span>Jenny Cantlay received funding from NERC and the RSPB for her doctoral research on avian vision whilst at Royal Holloway University.</span></em></p><p class="fine-print"><em><span>Graham Martin does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Our airspace has only started to become cluttered recently – many birds are struggling to navigate through it.Graham Martin, Emeritus Professor of Avian Sensory Science, University of BirminghamJenny Cantlay, PhD Candidate in Avian Sensory Ecology, Royal Holloway University of LondonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2124202023-09-04T17:37:53Z2023-09-04T17:37:53ZDogs don’t see life through rose-coloured glasses, nor in black and white<p>For a few months now, I’ve been treating six-year-old Samuel, who has the beginnings of myopia. He’s very quick for his age and often asks me questions about tests I give him, and about what I see inside his eyes. </p>
<p>But the last question surprised me. </p>
<p>Samuel knows that some people, like his father, don’t see colours well. But what about his little poodle, Scotch, he asked?</p>
<p>I’m not a veterinarian and don’t want to intrude on their domain of expertise. However, as an optometrist, I can offer some insights that might help answer Samuel’s question. </p>
<h2>Cones and rods</h2>
<p>Ambient light is composed of <a href="https://www.britannica.com/science/photon">particles (photons)</a>, which line up in rays. Light rays travel and strike objects. Some rays are absorbed, while others are reflected, depending on the characteristics of their surfaces and the composition of their materials. The wavelengths of the reflected rays determine the colour of the object as it is perceived by the eye. </p>
<p>Like everything about human vision, colour perception is complex. The retina, the sensitive part that lines the back of the eye, has two types of photon receptors: cones and rods. The cones, in the centre of the retina (fovea), perceive bright light and are <a href="https://askabiologist.asu.edu/rods-and-cones">responsible for colour perception</a>.</p>
<p>There are three types of cones. Each type contains a specific photo-pigment called opsin, which defines its nature. The opsin is produced under the influence of specific genes. The shortest opsin (“Cone S” for <em>short</em>) reacts mainly to blue light (420 nm). The longer one (“Cone L”) is more sensitive to orange-red light (560 nm) and the one in between (“Cone M” for <em>middle</em>) <a href="https://opentextbc.ca/biology/chapter/17-5-vision/">is activated in the presence of green (530 nm)</a>.</p>
<p>However, each cone reacts to each of the rays entering the eye. For example, a red ball will produce a weak response from the S cone (3/10), a slightly stronger response from the M cone (5/10) and a <a href="https://opentextbc.ca/biology/chapter/17-5-vision/">strong response from the L cone</a> (8/10). </p>
<p>The brain combines the signals emitted by each of these cones to form the colour it perceives. So, in the previous example, the perceived colour would be coded 3-5-8, corresponding to what we know as red. A pink colour might have the code 4-6-6, and blue, 8-6-3. Each combination of the 3-cone signals is unique, which allows us to appreciate different hues in all their variations. </p>
<p>That is, as long as the genetic code is intact. </p>
<p>The genes associated with colour vision can be mutated or defective, in which case the person will be partially or completely impaired. The best known of these anomalies is colour blindness (red-green deficiency or daltonism).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="perception of a plant according to a colour-blind person" src="https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=331&fit=crop&dpr=1 600w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=331&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=331&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=415&fit=crop&dpr=1 754w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=415&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=415&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Colour blindness is associated with difficulty in perceiving red and green.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>And what about animals?</h2>
<p>Colour vision, in humans as in animals, <a href="https://www.discoverwildlife.com/animal-facts/animal-vision-how-do-animals-see/">has developed throughout evolution</a> and results from the needs of each species according to their environment, the prey they hunt and the threats they need to avoid.</p>
<p>For example, birds have a fourth opsin that allows them to see ultraviolet (UV) light. Humans cannot perceive this light because our crystalline (internal) lens <a href="https://www.nwf.org/Magazines/National-Wildlife/2012/AugSept/Animals/Bird-Vision">filters UV rays</a>. UV rays influence birds’ behavioural decisions, including foraging and <a href="https://www.sciencedirect.com/science/article/abs/pii/S0065345408601059#:%7E:text=Publisher%20%20Summary,light%2C%20depending%20on%20the%20species.">their choice of a mate</a>.</p>
<p>So the colour vision of birds is more complex, with the result that the pigeon, which can perceive a myriad of colours, wins the <a href="https://nuscimagazine.com/the-world-through-the-eyes-of-a-pigeon/#:%7E:text=Though%20this%20range%20of%20vision,is%20one%20of%20these%20animal">award for best color vision among all species</a>.</p>
<p>Insects also perceive UV light. This function is essential for them to spot pollen, although their colour vision is very poor. Their eyes are made up of multiple lenses (ommatidia) that perceive <a href="https://www.mpg.de/14337047/how-flies-see-the-world">more movement than colour</a>. That’s much more practical while in fast flight.</p>
<p>Most forest-dwelling mammals have only two opsins. That’s because they lost the one associated with orange-red over the course of evolution. This explains why, unlike humans, these animals don’t perceive the orange bibs of hunters. </p>
<p>Snakes, on the other hand, are more sensitive to red and infrared light, thanks to their infrared receptors. This is an advantage when it comes to spotting prey, as <a href="https://phys.org/news/2006-08-snakes-vision-enables-accurate-prey.html">they can distinguish their heat even at night</a>. </p>
<p>Unsurprisingly, it’s the monkey that’s closest to the human, with its three opsins. It is said to be trichromatic. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="close-up of a black dog's eyes" src="https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Dogs only perceive yellow-green and violet-blue. Colours are perceived as paler, like pastels.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>Back to Scotch</h2>
<p>The vision of dogs — such as our friend Scotch — is <a href="https://ophtalmoveterinaire.com/maladies_oculaires/vision-comment-voit-mon-chien/#:%7E:text=For%20r%C3%A9sumer%2C%20the%20vision%20of,for%20his%20life%20of%20dog.">quite different</a>. </p>
<p>Unlike humans, dogs’ eyes are located on the side of the skull. As a result, dogs have a wider field of vision (250 to 280 degrees), but less simultaneous vision. </p>
<p>So Scotch’s vision of movement is well developed throughout his visual field. But his central vision is actually six times weaker than ours. This is equivalent to the vision of a very myopic person not wearing glasses. Why? Because the dog’s retina contains no fovea, and therefore fewer cones. </p>
<p>But while dogs eyes have fewer cones, they have more rods. And as an added bonus, they have an extra layer of the retina, called the tapetum lucidum — or carpet. When combined, these ingredients mean dogs see better in dim light and at night. This layer receives light and reflects it back onto the retina for a second exposure. This explains why your dog’s eyes seem to glow at night.</p>
<p>When it comes to colours, dogs are dichromats. They perceive only yellow-green and violet-blue. Colours are perceived paler, like pastels. And some colours don’t contrast: that’s why a red ball on green grass will appear to them as pale yellow on a grey background, with little contrast.</p>
<p>So it’s possible, depending on the colour of the ball, that Scotch will not see it, and as a result, will gaze up at Samuel with a lost look. As for the infrared, he perceives heat through his nose, not through his eyes.</p>
<p>Cats are also dichromats. Their vision is therefore similar to that of dogs, but their colour palette is different — more oriented towards violet and green. Having no perception of red-green, they are essentially colour-blind. They are also very short-sighted. Their clear vision is limited to a few meters in front of them.</p>
<p>Throughout cats’ evolution, other senses came to compensate for this. Among other things, although they only perceive certain contrasts, they are <a href="https://www.wired.com/2013/10/cats-eye-view/">formidable at perceiving movement</a>. Mice move quickly! </p>
<p>Every species adapts to its environment, and humans are no exception. Who knows what our colour vision will be like 500 years from now, after we’ve been exposed to more and more electronic devices and artificial colours? </p>
<p>But that’s a question for Samuel to answer when he’s older.</p><img src="https://counter.theconversation.com/content/212420/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Langis Michaud ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>Your faithful companion sees the world differently than you do, but it’s a mistake to assume dogs only see black, white and shades of grey.Langis Michaud, Professeur Titulaire. École d'optométrie. Expertise en santé oculaire et usage des lentilles cornéennes spécialisées, Université de MontréalLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2038372023-05-17T12:39:23Z2023-05-17T12:39:23ZBees can learn, remember, think and make decisions – here’s a look at how they navigate the world<figure><img src="https://images.theconversation.com/files/526312/original/file-20230515-24407-1yxhj8.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2286%2C1560&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A bumblebee lands on the flowers of a white sloe bush. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/april-2022-saxony-anhalt-kathendorf-a-bumblebee-lands-on-news-photo/1240227459">Soeren Stache/picture alliance via Getty Images</a></span></figcaption></figure><p>As trees and flowers blossom in spring, bees emerge from their winter nests and burrows. For many species it’s <a href="https://theconversation.com/spring-signals-female-bees-to-lay-the-next-generation-of-pollinators-134852">time to mate</a>, and some will start new solitary nests or colonies. </p>
<p>Bees and other pollinators are essential to human society. They provide about one-third of the <a href="https://theconversation.com/a-bee-economist-explains-honey-bees-vital-role-in-growing-tasty-almonds-101421">food we eat</a>, a service with a global value estimated at <a href="https://doi.org/10.1038/nature20588">up to $US577 billion annually</a>.</p>
<p>But bees are interesting in many other ways that are less widely known. In my new book, “<a href="https://islandpress.org/books/what-bee-knows">What a Bee Knows: Exploring the Thoughts, Memories, and Personalities of Bees</a>,” I draw on my experience <a href="https://scholar.google.com/citations?user=tqms8REAAAAJ&hl=en">studying bees for almost 50 years</a> to explore how these creatures perceive the world and their amazing abilities to navigate, learn, communicate and remember. Here’s some of what I’ve learned.</p>
<h2>It’s not all about hives and honey</h2>
<p>Because people are widely familiar with honeybees, many assume that all bees are social and live in hives or colonies with a queen. In fact, only about 10% of bees are social, and most types don’t make honey.</p>
<p>Most bees lead solitary lives, digging nests in the ground or finding abandoned beetle burrows in dead wood to call home. Some bees are cleptoparasites, <a href="https://www.sciencefriday.com/articles/death-and-thievery-in-the-colony/">sneaking into unoccupied nests to lay eggs</a>, in the same way that cowbirds lay their eggs in other birds’ nests and let the unknowing foster parents <a href="https://madisonaudubon.org/blog/2018/8/9/into-the-nest-cowbirds-everybodys-favorite-villain">rear their chicks</a>.</p>
<p>A few species of tropical bees, known as vulture bees, survive by <a href="https://doi.org/10.1128/mBio.02317-21">eating carrion</a>. Their guts contain acid-loving bacteria that enable the bees to digest rotting meat. </p>
<p><div data-react-class="InstagramEmbed" data-react-props="{"url":"https://www.instagram.com/p/CGWgbHdgmBB/?utm_source=ig_web_copy_link\u0026igshid=MzRlODBiNWFlZA==","accessToken":"127105130696839|b4b75090c9688d81dfd245afe6052f20"}"></div></p>
<h2>Busy brains</h2>
<p>The world looks very different to a bee than it does to a human, but bees’ perceptions are hardly simple. Bees are intelligent animals that <a href="https://doi.org/10.1016/j.anbehav.2016.05.005">likely feel pain</a>, remember patterns and odors and even <a href="https://doi.org/10.1242/jeb.01929">recognize human faces</a>. They <a href="https://doi.org/10.1006/nlme.1996.0069">can solve mazes</a> and other problems and use simple tools. </p>
<p>Research shows that bees <a href="https://doi.org/10.1016/j.cub.2020.12.027">are self-aware</a> and may even have a <a href="https://doi.org/10.1016/j.cub.2017.08.008">primitive form of consciousness</a>. During the six to 10 hours bees spend <a href="https://doi.org/10.7717/peerj.9583">sleeping daily</a>, <a href="https://doi.org/10.1016/j.neubiorev.2014.09.020">memories are consolidated</a> within their amazing brains – organs the size of a poppy seed that contain 1 million nerve cells. There are some indications that <a href="https://doi.org/10.1016/j.cub.2015.09.001">bees might even dream</a>. I’d like to think so. </p>
<h2>An alien sensory world</h2>
<p>Bees’ sensory experience of the world is markedly different from ours. For example, humans see the world through the primary colors of <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/vision/colcon.html">red, green and blue</a>. Primary colors for bees are <a href="https://doi.org/10.1007/978-3-642-71496-2_15">green, blue and ultraviolet</a>.</p>
<p>Bees’ vision is <a href="https://doi.org/10.1146/annurev.ento.010908.164537">60 times less sharp than that of humans</a>: A flying bee can’t see the details of a flower until it is about 10 inches away. However, bees can see hidden ultraviolet floral patterns that are invisible to us, and those patterns lead the bees to flowers’ nectar.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/kQ8GRJp8bVg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Naturalist David Attenborough uses ultraviolet light to show how flowers may appear different to bees than to humans.</span></figcaption>
</figure>
<p>Bees also can spot flowers by detecting color changes at a distance. When humans watch film projected at 24 frames per second, the individual images appear to blur into motion. This phenomenon, which is called the <a href="https://www.britannica.com/science/movement-perception/Apparent-movement#ref488126">flicker-fusion frequency</a>, indicates how capable our visual systems are at resolving moving images. Bees have a much higher flicker-fusion frequency – you would have to play the film 10 times faster for it to look like a blur to them – so they can fly over a flowering meadow and <a href="https://doi.org/10.1007/BF00610583">see bright spots of floral color</a> that wouldn’t stand out to humans.</p>
<p>From a distance, bees detect flowers by scent. A honeybee’s sense of smell is <a href="https://doi.org/10.1371/journal.pone.0009110">100 times more sensitive</a> than ours. Scientists have used bees to sniff out chemicals <a href="https://entomologytoday.org/2013/11/25/can-trained-bees-detect-cancer-in-patients/">associated with cancer</a> and <a href="https://www.cbsnews.com/boston/news/boston-researchers-train-bees-to-detect-diabetes/">with diabetes</a> on patients’ breath and to detect the presence of <a href="https://www.technologyreview.com/2006/12/07/227361/using-bees-to-detect-bombs/">high explosives</a>. </p>
<p>Bees’ sense of touch is also highly developed: They can feel tiny fingerprint-like ridges <a href="https://doi.org/10.1073/pnas.82.14.4750">on the petals of some flowers</a>. Bees are <a href="https://doi.org/10.1080/0005772X.1995.11099233">nearly deaf</a> to most airborne sounds, unless they are very close to the source, but are sensitive if they are standing on a vibrating surface. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1348645052134944771"}"></div></p>
<h2>Problem solvers</h2>
<p>Bees <a href="https://doi.org/10.1080/0005772X.1995.11099233">can navigate mazes</a> as well as mice can, and studies show that they are self-aware of their body dimensions. For example, when fat bumblebees were trained to fly and then walk through a slit in a board to get to food on the other side, the bees <a href="https://doi.org/10.1073/pnas.2016872117">turned their bodies sideways and tucked in their legs</a>. </p>
<p>Experiments by Canadian researcher Peter Kevan and Lars Chittka in England demonstrated remarkable feats of bee learning. Bumblebees were trained to pull a string – in other words, to use a tool – connected to a plastic disk with hidden depressions filled with sugar water. They could see the sugar wells but couldn’t get the reward <a href="https://doi.org/10.1371/journal.pbio.1002564">except by tugging at the string</a> until the disk was uncovered.</p>
<p>Other worker bees were placed nearby in a screen cage where they could see what their trained hive mates did. Once released, this second group also pulled the string for the sweet treats. This study demonstrated what scientists term <a href="https://www.britannica.com/science/social-learning">social learning</a> – acting in ways that reflect the behavior of others.</p>
<h2>Pollinating with vibrations</h2>
<p>Even pollination, one of bees’ best-known behaviors, can be much more complicated than it seems. </p>
<p>The basic process is similar for all types of bees: Females carry pollen grains, the sex cells of plants, on their bodies from flower to flower as they collect pollen and nectar to feed themselves and their developing grubs. When pollen rubs off onto <a href="https://www.amnh.org/learn-teach/curriculum-collections/biodiversity-counts/plant-identification/plant-morphology/parts-of-a-flower">a flower’s stigma</a>, the result is pollination. </p>
<p>My favorite area of bee research examines a method called <a href="https://doi.org/10.1016/j.pbi.2013.05.002">buzz pollination</a>. Bees use it on about 10% of the world’s 350,000 kinds of flowering plants that have special <a href="https://www.amnh.org/learn-teach/curriculum-collections/biodiversity-counts/plant-identification/plant-morphology/parts-of-a-flower">anthers</a> – structures that produce pollen. </p>
<p>For example, a tomato blossom’s five anthers are pinched together, like the closed fingers of one hand. Pollen is released through one or two small pores at the end of each anther. </p>
<p>When a female bumblebee lands on a tomato flower, she bites one anther at the middle and contracts her flight muscles from <a href="https://doi.org/10.1093/jxb/erab428">100 to 400 times per second</a>. These powerful vibrations eject pollen from the anther pores in the form of a cloud that strikes the bee. It all happens in just a few tenths of a second. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/SZrTndD1H10?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Bumblebees demonstrate buzz pollination on a Persian violet blossom.</span></figcaption>
</figure>
<p>The bee hangs by one leg and scrapes the pollen into “baskets” – structures on her hind legs. Then she repeats the buzzing on the remaining anthers before moving to different flowers.</p>
<p>Bees also use buzz pollination on the flowers of blueberries, cranberries, eggplant and kiwi fruits. My colleagues and I are conducting experiments to determine the biomechanics of <a href="https://doi.org/10.1098/rsif.2022.0040">how bee vibrations eject pollen from anthers</a>. </p>
<h2>Planting for bees</h2>
<p>Many species of bees are <a href="https://theconversation.com/bees-face-many-challenges-and-climate-change-is-ratcheting-up-the-pressure-190296">declining worldwide</a>, thanks to stresses including <a href="http://dx.doi.org/%2010.1126/science.1255957">parasites, pesticides and habitat loss</a>.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/526311/original/file-20230515-18664-v796la.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Wood cubes filled with twigs and bricks." src="https://images.theconversation.com/files/526311/original/file-20230515-18664-v796la.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/526311/original/file-20230515-18664-v796la.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/526311/original/file-20230515-18664-v796la.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/526311/original/file-20230515-18664-v796la.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/526311/original/file-20230515-18664-v796la.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/526311/original/file-20230515-18664-v796la.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/526311/original/file-20230515-18664-v796la.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A backyard ‘insect hotel’ for solitary bees and other nesting insects, made from stems, bricks and wood blocks.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/insect-hotel-for-solitary-bees-and-artificial-nesting-place-news-photo/601067110">Arterra/Universal Images Group vis Getty Images</a></span>
</figcaption>
</figure>
<p>Whether you have an apartment window box or several acres of land, you can do a few <a href="https://theconversation.com/to-help-insects-make-them-welcome-in-your-garden-heres-how-153609">simple things to help bees</a>. </p>
<p>First, plant native wildflowers so that blooms are available in every season. Second, try to avoid using insecticides or herbicides. Third, provide open ground where burrowing bees can nest. With luck, soon you’ll have some buzzing new neighbors.</p><img src="https://counter.theconversation.com/content/203837/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stephen Buchmann does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Scientists are learning amazing things about bees’ sensory perception and mental capabilities.Stephen Buchmann, Adjunct Professor of Entomology and of Ecology and Evolutionary Biology, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2029522023-04-24T12:24:51Z2023-04-24T12:24:51ZCan rainbows form in a circle? Fun facts on the physics of rainbows<figure><img src="https://images.theconversation.com/files/521644/original/file-20230418-20-88ojk7.jpg?ixlib=rb-1.1.0&rect=0%2C13%2C8959%2C5547&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The higher your vantage point, the more likely you’ll see more of the rainbow’s circle. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/double-rainbow-hangs-in-the-sky-above-buildings-and-the-news-photo/1405823752">Chen Hui/VCG via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption"></span>
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Can rainbows form in a circle? – Henry D., age 7, Cambridge, Massachusetts</strong></p>
</blockquote>
<hr>
<p>The legend goes that there is a pot of gold hidden at the end of every rainbow. But is there really an “end” to a rainbow, and can we ever get to it?</p>
<p>Most us go through life seeing rainbows only as arches of color in the sky, but that’s only half of what is really a circle of color.</p>
<p>Normally, when you look at a rainbow, the Earth’s horizon in front of you hides the bottom half of the circle. But if you are standing on a mountain where you can see both above and below you, and the sun is behind you and it is misty or has just rained, chances are good that you will see more of the rainbow’s circle.</p>
<figure class="align-center ">
<img alt="A rainbow in the mist below a waterfall in Iceland." src="https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&rect=0%2C52%2C5000%2C3270&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">How full this rainbow looks depends in part on how high up you’re standing while watching sunlight hit the waterfall’s mist.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/iceland-south-coast-skogarfoss-waterfall-rainbow-news-photo/452271798">Wolfgang Kaehler/LightRocket via Getty Images</a></span>
</figcaption>
</figure>
<p>To see the full circle, however, you will have to be in an airplane, literally above the clouds. Or you could create your own rainbow. I am <a href="https://www.uml.edu/Honors/People/chowdhury-partha.aspx">a physicist</a>, and I’ll explain how to do that in a minute.</p>
<h2>How a rainbow forms</h2>
<p><a href="https://scijinks.gov/rainbow/">Rainbows form</a> when sunlight from behind you hits millions of tiny round water droplets in front of you and bounces back to your eyes.</p>
<p>As a sunbeam hits a droplet at an angle, it bends into the water and separates out into a spectrum of colors. Scientists <a href="https://global.canon/en/technology/s_labo/light/001/02.html">call the bending of light “refracting</a>.” The colors separate because each “color” of light <a href="https://www.metoffice.gov.uk/weather/learn-about/weather/optical-effects/rainbows/colours-of-the-rainbow">travels with a different speed</a> in water, or, for that matter, any transparent material that light can travel through, like glass in a prism.</p>
<p>When the colors hit the back wall of the water droplet, the angle is now too shallow for them to bend out into the air, so they reflect back into the water droplet and return to its entrance wall. From there, the colors can bend out again into air and reach your eye.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/q73VNpFA-0Q?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The United Kingdom’s Meteorology Office explains how light refracts, or bends, in a water droplet or a prism.</span></figcaption>
</figure>
<p>As you look at these droplets, the different colors happen to bunch up at a slightly different angle, and each color forms the <a href="https://atoptics.co.uk/rainbows/primcone.htm">circular rim of a cone</a> with your eye at the tip of the cone. And, voila, you have your own personal rainbow.</p>
<p>The droplets that send the colors to your eye cannot send them to anyone else, so even though everyone near you sees the same rainbow at a distance, each person really sees their own slightly different rainbow. It’s all in the eye of the beholder.</p>
<p>For rainbows to form, the shape of the water droplets has to be very close to a sphere for all of them to bend and reflect the colors in harmony. This happens for very small droplets, such as a fine mist, or just after a rain shower when the air is just moist. As the droplets get larger, gravity distorts their shape and the rainbow vanishes.</p>
<figure class="align-center ">
<img alt="An elephant in water closes its eyes while the photographer captures a rainbow across its trunk and forehead." src="https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Even though it looks like this elephant is bathing in a rainbow, the elephant wouldn’t see it in the same way.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/an-elephant-is-pictured-under-a-rainbow-of-water-sprayed-to-news-photo/1242012110">Mads Claus Rasmussen / Ritzau Scanpix / AFP</a></span>
</figcaption>
</figure>
<p>A rainbow is not physically present where it appears to be, similar to your image in a mirror. So, I’m sorry to say that you can never actually reach your rainbow. And, alas, nobody can ever find that pot of gold.</p>
<p>But you can <a href="https://www.youtube.com/watch?v=dIdE-pqYqbs">create your own rainbow</a>. </p>
<h2>How to create and see a circular rainbow</h2>
<p>One experiment you can try in summer is to turn on a sprinkler hose using the “mist” setting. Remember to have the sun behind you. If you create a fine mist screen in front of you and look at your shadow, you might see a rainbow. </p>
<figure class="align-center ">
<img alt="A young boy plays in a fountain, with a rainbow overhead." src="https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=396&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=396&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=396&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=497&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=497&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=497&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">It might take some work, but you can see your own full-circle rainbows in the mist.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/young-boy-cools-off-under-a-rainbow-in-a-fountain-on-a-warm-news-photo/1266045824">Gary Hershorn/Getty Images</a></span>
</figcaption>
</figure>
<p>It is not difficult to see colors, but to see a full circle, you will need some patience and practice, just like scientists.</p>
<p>So next time you are on an airplane, grab the window seat. If you are flying a little above the cloud cover, keep a lookout for the small shadow of your plane on the clouds. That means the sun is behind you. </p>
<p>The clouds are tiny water droplets, so chances are you may see a small circle of color around the shadow of the airplane. This phenomenon is <a href="https://science.howstuffworks.com/nature/climate-weather/atmospheric/pilots-glory-rainbow-airplane-shadow.htm">nicknamed “pilot’s glory</a>,” because pilots who fly all the time and have a good view from the cockpit have a better chance of seeing it.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An airplane's shadow has a circular rainbow around it as it flies over mountains." src="https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=563&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The circular rainbow you see around an airplane’s shadow is called ‘pilot’s glory.’</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/imatty35/6708114761/">Matthew Straubmuller/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>And if you really can’t wait to see what it looks like, there’s <a href="https://education.nationalgeographic.org/resource/rainbow/">always the internet</a>.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/202952/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Partha Chowdhury does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Each rainbow is personal – the rainbow you see isn’t exactly the same rainbow the next person sees. It’s all in the eye of the beholder.Partha Chowdhury, Professor of Physics, UMass LowellLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2033822023-04-07T15:56:02Z2023-04-07T15:56:02ZOn April 8, 2024, parts of Ontario, Québec, the Maritimes and Newfoundland will see a total eclipse of the sun. Here’s how to get ready for it.<figure><img src="https://images.theconversation.com/files/519687/original/file-20230405-22-8wx57z.jpg?ixlib=rb-1.1.0&rect=25%2C11%2C1862%2C1212&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Watching a solar eclipse is always fascinating. During the phase when the moon completely obstructs the sun, daylight gives way to a deep twilight sky.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>You might not know exactly what you will be doing a year from now, on April 8, 2024. It’s pretty hard to predict a year in advance. However, on that date, <a href="https://solarsystem.nasa.gov/eclipses/2024/apr-8-total/where-when/">a total solar eclipse will occur in parts of Mexico, the United States and Canada — including parts of southern Ontario and Québec, New Brunswick, Nova Scotia, Prince Edward Island and Newfoundland</a> — a rare phenomenon. </p>
<p>The total solar eclipse will be visible in locations including: Niagara Falls and Hamilton, Ont.; Montréal; Fredericton, N.B.; western P.E.I.; the northern tip of Cape Breton, N.S.; and Gander, Nfld.</p>
<p>Cities like Toronto and Ottawa will be just beyond the path of the total solar eclipse. </p>
<p>While partial solar eclipses happen quite frequently, the total disappearance of the sun behind the moon only occurs <a href="https://espacepourlavie.ca/en/total-or-annular-solar-eclipse">when the moon is closer to our planet or the sun is at its furthest point from it</a>. It is a question of the size of the moon compared to the sun. When the two are perfectly aligned, it creates a shadow cone that allows people on Earth who are within this narrow band to enjoy the unique spectacle of a total eclipse. </p>
<p>On average, this alignment only occurs <a href="https://espacepourlavie.ca/en/frequency-solar-eclipses">once every 375 years</a>, but it can vary. For example, the last total eclipse visible in Montréal occurred on Aug. 31, 1932. Other regions in Canada have not been as lucky. In St. John’s, Nfld., the last total eclipse was on Feb. 3, 1440, and locals will have to wait a total of 765 years for the next one, which will happen on July 17, 2205! The record belongs to Regina, Sask., which had a total eclipse in 54 BC, but will not see another one until Oct. 17, 2153 — or a total of 2207 years! </p>
<p>So try not to miss the total eclipse in places like Montréal in 2024. If you do, you’ll have to go to a location like <a href="https://espacepourlavie.ca/en/frequency-solar-eclipses">Calgary for the next one, in 20 years</a>. </p>
<p>Yet the phenomenon does pose significant risks to eye health. As an optometrist, I am very concerned about eye health issues. I certainly wouldn’t want anyone to go blind after watching a solar eclipse without properly protecting their eyes.</p>
<h2>Watch it, but protect yourself</h2>
<p>Watching a total solar eclipse is always fascinating. During the phase when the moon completely obstructs the sun, daylight is transformed into a deep twilight sky. The sun’s outer atmosphere (known as the sun’s corona) gradually appears, <a href="https://solarsystem.nasa.gov/eclipses/2024/apr-8-total/overview/">shining like a halo around the moon</a>. The bright stars and planets become more visible in the sky.</p>
<p>In daylight, the sun usually emits visible light that is so intense we cannot look directly at it for very long. If our eye ever looks directly at the sun, we have the reflex of turning away from it immediately, after <a href="https://ehs.lbl.gov/resource/documents/radiation-protection/non-ionizing-radiation/light-and-infrared-radiation/#:%7E:text=Prolonged%20exposure%20to%20IR%20radiation,eye%2C%20swelling%2C%20or%20hemorrhaging">an average of only 0.25 seconds</a>. This reflex provides natural protection for eyes against the harmful rays of the sun, some of which — notably ultraviolet and infrared radiation — are not visible. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="total solar eclipse" src="https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519350/original/file-20230404-18-rpgn0r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">During a total solar eclipse, the sun’s outer atmosphere (called the solar corona) gradually appears, shining like a halo around the moon that faces it.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>Ultraviolet radiation (UV)</h2>
<p>UVs accounts for <a href="https://ehs.lbl.gov/resource/documents/radiation-protection/non-ionizing-radiation/light-and-infrared-radiation/#:%7E:text=Prolonged%20exposure%20to%20IR%20radiation,eye%2C%20swelling%2C%20or%20hemorrhaging.">seven per cent of solar radiation</a>. They are partly absorbed by the cornea (the clear part at the front of the eye) and the crystalline lens (the natural lens inside the eye), without causing any damage, unless the exposure is too great. </p>
<p>In such cases, depending on the amount of UV radiation it absorbs, the cornea may develop inflammation, known as keratitis. The lens, in turn, loses its transparency — this is called a cataract. Other impacts can be expected, such as the development of <a href="https://www.nei.nih.gov/about/news-and-events/news/protecting-your-eyes-suns-uv-light#:%7E:text=Prolonged%20exposure%20to%20UV%20rays,are%20linked%20to%20UV%20exposure">small cysts (pinguecula) on the conjunctiva (white of the eye) or a membrane invading the cornea (pterygium)</a>.</p>
<p>Eyelids can also develop skin cancers. The upper eyelid, which is usually not exposed on the outside when our eyes are open, is particularly at risk when we lie on the beach with our eyes closed without protection. Finally, UV light predisposes us to <a href="https://theconversation.com/macular-degeneration-is-a-leading-cause-of-blindness-heres-how-to-prevent-it-160683">macular degeneration</a>, which is a damage to our best retinal cells and can result in varying degrees of vision loss.</p>
<p>These <a href="https://www.aao.org/eye-health/tips-prevention/sun">diseases</a> all develop as a result of direct radiation, but can also come about when the sun’s rays are strongly reflected by surfaces such as snow (snow ophthalmia), sand or water. It is therefore recommended to wear protective eyewear that cuts out all UV rays (UV400 protection) when you plan to spend more than a few minutes in the sun. For both <a href="https://theconversation.com/summer-is-here-why-you-need-to-protect-your-childrens-eyes-116498">children</a> and adults, the frame should wrap around the eyes, so that no rays pass through the side or top.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="child wears sunglasses at the beach" src="https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=390&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=390&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=390&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=490&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=490&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519354/original/file-20230404-2216-nwlh6e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=490&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">For both children and adults, the frame of sunglasses should wrap around the eyes, so that no rays pass through from the side or top.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>Infrared radiation (IR)</h2>
<p>IRs make up the majority of the radiation emitted by the sun — <a href="https://ehs.lbl.gov/resource/documents/radiation-protection/non-ionizing-radiation/light-and-infrared-radiation/#:%7E:text=Prolonged%20exposure%20to%20IR%20radiation,eye%2C%20swelling%2C%20or%20hemorrhaging">54 per cent</a>. We feel the effects because it is thermal radiation, which is accompanied by heat. </p>
<p>While the cornea (burning) and lens (cataract) can also be affected by IR, it is more the retina that can suffer from inappropriate exposure to IR. Again, it is a question of intensity and duration. As with UV radiation, the more intense the radiation, the more permanent damage will occur in a short period of time.</p>
<p>IR damage to the retina destroys the cells that allow us to see and ultimately creates a scotoma, a permanent black spot in our field of vision. This is a cause of blindness. </p>
<h2>Eclipse and radiation</h2>
<p>When the Sun is only partially hidden (partial eclipse), the UV and IR radiation is as important as in full sunlight. However, because of the reduced luminosity, we no longer have the natural reflex of turning our eyes away. So it may seem more comfortable to observe the sun for several seconds or even minutes. Without protection, this type of exposure can lead to the pathologies described above and contribute to blindness if the central retina is affected. <a href="https://www.theguardian.com/us-news/video/2017/aug/21/donald-trump-look-directly-sun-eclipse-video">U.S. President Donald Trump was reminded of this in 2017</a>, when he watched a partial eclipse without protection, putting his vision at risk. </p>
<p>During a total eclipse, however, it is possible, during the short duration of the total obstruction of the sun (one minute 37 seconds), to <a href="https://www.nasa.gov/content/eye-safety-during-a-total-solar-eclipse/#:%7E:text=During%20the%20short%20time%20when,put%20back%20on%20your%20glasses.">look at the solar corona without protection</a>. But you must be very vigilant and remember to put protection back in place as soon as the Moon starts to move and the radiation becomes present again, even though the ambient luminosity is still reduced. </p>
<p>The same precautions should be taken when viewing the eclipse directly through binoculars, a telescope, a camera or other optical means. For example, do not look at your phone screen with the naked eye when trying to take pictures of the eclipse. The rays are not blocked by these instruments and can cause significant eye damage. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Trump points at the sun" src="https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519351/original/file-20230404-988-6obvvo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">President Donald Trump points at the sun without protective glasses during the partial solar eclipse on Aug. 21, 2017, at the White House in Washington, D.C.</span>
<span class="attribution"><span class="source">(AP Photo/Andrew Harnik)</span></span>
</figcaption>
</figure>
<h2>A question of protection</h2>
<p>So, what kind of eye protection are we talking about exactly? Sunscreens that can be mounted in glasses or in temporary glasses, made of cardboard, but that cover the entire surface of the eye perfectly. Once again, it is important to avoid leaving a gap between the eye and the protective screen through which harmful radiation can enter. Permitted filters <a href="https://www.aao.org/eye-health/tips-prevention/solar-eclipse-eye-safety">must meet ISO-12312-2</a>.</p>
<p>Before wearing such filters, be sure to follow the instructions provided with the equipment. It is very important for parents to ensure that children wear the filters properly and do not play with them. When the observation is over, do not remove the filters while you are still looking at the sun: look away, turn your back to the sun and remove the filters. Then don’t look at the sky anymore. </p>
<h2>If ever…</h2>
<p>Damage to the cornea and retina can occur within hours of exposure, but not always immediately. If you have ever been inadvertently or recklessly exposed, monitor your vision in the hours after the eclipse. If you notice any blurring or changes in your vision, you should consult an optometrist or ophthalmologist as soon as possible. </p>
<p>Many activities will be organized for the arrival of the total eclipse. To make the most of this unique event, watch for announcements from organizations such as <a href="https://espacepourlavie.ca/en">Space for Life</a>, institutions such as the Université de Montréal, or your local astronomy clubs. These organizations will provide information, may provide protective glasses/filters and, most importantly, will help you to better understand the phenomenon. </p>
<p>See you in a year’s time! But in the meantime, whether young and old, let’s all protect our eyes properly.</p><img src="https://counter.theconversation.com/content/203382/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Langis Michaud ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>Some parts of North America will witness a total solar eclipse in April 2024. This may seem far away, but you should think about preparing for this rare and fascinating phenomenon.Langis Michaud, Professeur Titulaire. École d'optométrie. Expertise en santé oculaire et usage des lentilles cornéennes spécialisées, Université de MontréalLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1966342023-01-08T13:26:53Z2023-01-08T13:26:53ZType 2 diabetes in young people puts their eyes at risk<figure><img src="https://images.theconversation.com/files/501160/original/file-20221214-15950-g5r5q3.jpg?ixlib=rb-1.1.0&rect=5%2C7%2C989%2C654&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">When it comes to eye care, regular visits to the optometrist or ophthalmologist can detect the early signs of diabetic damage.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>Sixteen-year-old Karl is seen for the first time in my optometry practice. He was referred to me for a fluctuating vision problem. During his examination, I saw signs suggesting he may have diabetes, which could have explained the fluctuating vision. This suspicion became a reality when his family doctor confirmed the diagnosis. Karl’s world was turned upside down.</p>
<p>As an optometrist, I invite you to dive into a reality that should concern us all.</p>
<h2>What is diabetes?</h2>
<p>Diabetes is an insidious disease. Its symptoms <a href="https://www.mayoclinic.org/diseases-conditions/type-2-diabetes-in-children/symptoms-causes/syc-20355318">(thirst, need to urinate often, fatigue, weight loss, darker skin areas on the neck and underarms)</a> often go unnoticed, at least in the early stages of the disease.</p>
<p>Diabetes affects the lives of <a href="https://data.worldbank.org/indicator/SH.STA.DIAB.ZS?locations=XU">one in 14 people in Canada (7 per cent) and one in 10 in North America (10 per cent)</a>.</p>
<p>Two types of diabetes can be diagnosed:</p>
<ul>
<li><p><a href="https://www.diabete.qc.ca/en/understand-diabetes/all-about-diabetes/types-of-diabetes/type-1-diabetes/">Type 1</a>, which is insulin-dependent and develops when the body cannot produce the insulin needed to metabolize the sugars we ingest and which feed our tissues</p></li>
<li><p><a href="https://www.canada.ca/en/public-health/services/diseases/type-2-diabetes.html">Type 2</a>, which develops when insulin is produced, but in insufficient quantities. Sometimes the insulin that is produced is ineffective in doing its job.</p></li>
</ul>
<p>Type 1 diabetes is usually associated with the development of the disease in childhood and adolescence. Type 2, the most common, usually develops later in life, <a href="https://www.diabete.qc.ca/en/understand-diabetes/all-about-diabetes/types-of-diabetes/">often after age 50</a>.</p>
<h2>A counter-intuitive diagnosis, but not a rare one</h2>
<p>From this definition, it would have been logical to conclude that Karl was affected by Type 1 diabetes, the course and treatment of which are well controlled by physicians. However, in his case, and after the required testing, his doctor identified Type 2 diabetes. This diagnosis is counter-intuitive and poses significant challenges. The speed of onset, the initial severity of the disease and the mechanisms of resistance, or of reduced insulin secretion, may be different in patients who develop the disease at a younger age <a href="https://pubmed.ncbi.nlm.nih.gov/15735201/">than in adults</a>.</p>
<p>In addition, treatment options, involving trial and error, become more complex due to the much longer duration of this type of disease when it starts at a young age. Both major and minor changes <a href="https://pubmed.ncbi.nlm.nih.gov/12090830/">that affect the blood vessels in the Type 2 diabetic patient</a> can have serious consequences that are difficult to predict since the course of treatment can continue for 40 to 60 years.</p>
<p>However, Karl’s situation is not exceptional. <a href="https://www.thelancet.com/pdfs/journals/landia/PIIS2213-8587(17)30186-9.pdf">More and more young people and adolescents</a>, especially those who are <a href="https://pubmed.ncbi.nlm.nih.gov/12241736/">overweight, obese, and sedentary</a>, are affected by Type 2. Almost 75 per cent of them have <a href="https://www.cdc.gov/diabetes/basics/type2.html">parents or siblings with diabetes</a>.</p>
<p>While at first sight, this confirms genetics as a risk factor for developing the disease, in this specific case, it was more a consequence of <a href="https://www.cdc.gov/diabetes/basics/type2.html">poor lifestyle habits, especially dietary habits, and lack of physical activity</a>, which are often shared by the whole family.</p>
<h2>Impact on vision</h2>
<p>The fact that Karl developed Type 2 diabetes earlier, rather than later in life also puts him at a higher risk of developing eye complications. An <a href="https://jamanetwork.com/journals/jamaophthalmology/fullarticle/2786928">article</a> about this topic recently caught my attention. This study looked at the records of 1,362 people with diabetes living in Minnesota, so, in North America and then extrapolate to Canada. The data was compiled between 1970 and 2019, which also allows us to measure the evolution of the situation over the last decades.</p>
<p>The results are astonishing: young people with Type 2 diabetes (compared to Type 1 diabetics of the same age) are 88 times more likely to develop retinopathy (abnormal blood vessels and/or hemorrhages in the retina). In addition, the risk of this retinopathy becoming “proliferative,” and therefore threatening to vision, is increased 230 times. There is also a 49-fold increase in the risk of fluid accumulation in the retina (macular edema) and a 243-fold increase in the risk of developing a mature cataract at a young age. The latter requires surgery which is riskier in young people than in the case of age-related senile cataracts.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/500479/original/file-20221212-113662-60amw4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="photograph of a fundus" src="https://images.theconversation.com/files/500479/original/file-20221212-113662-60amw4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500479/original/file-20221212-113662-60amw4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500479/original/file-20221212-113662-60amw4.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500479/original/file-20221212-113662-60amw4.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500479/original/file-20221212-113662-60amw4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500479/original/file-20221212-113662-60amw4.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500479/original/file-20221212-113662-60amw4.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Vascular and metabolic complications of diabetes visible on the fundus (hemorrhages, exudates).</span>
<span class="attribution"><span class="source">(Langis Michaud)</span>, <span class="license">Fourni par l'auteur</span></span>
</figcaption>
</figure>
<p>What should we remember from this? That the major problems, which often require surgical interventions to save vision, occur much more rapidly in young Type 2 diabetics than in those affected by Type 1. These patients must therefore be followed more closely. Indeed, almost one in two Type 2 patients will develop some form of retinopathy within one to eight years of diagnosis. In comparison, one in three Type 1 diabetics will develop retinopathy between six and 10 years following diagnosis.</p>
<h2>Significant repercussions</h2>
<p>Already having increased significantly in the last 10 years, the prevalence (number of cases) of Type 2 diabetes in young people is predicted to <a href="https://pubmed.ncbi.nlm.nih.gov/23173134/">quadruple by 2050</a>. This prediction is most alarming for health professionals, but also for policymakers and managers of public health agencies. The lifetime cost of direct medical care for a single diabetic patient aged 25-44 years was <a href="https://pubmed.ncbi.nlm.nih.gov/23953350/">US$125,000 in 2013</a>. These costs have since increased and many more dollars need to be added to cover the period between 15 and 25 years, which is not taken into account. Indeed, if 20 per cent of the youth population develops diabetes by 2050, millions (perhaps billions?) of health-care dollars will have to be spent on their care by our governments.</p>
<p>The long-term quality of life of people with diabetes is also reduced. <a href="https://pubmed.ncbi.nlm.nih.gov/30345893/">Another study</a>, this time of young people with Type 1 diabetes, shows that their disease has a negative impact on their life. They have to devote a lot of time to their care (missing activities with their friends). And the burden of their disease on their relatives weighs heavily on their shoulders. The fear of hypoglycemia (lack of sugar that can lead to coma) or of developing serious complications of the disease also affects them. Achieving autonomy is more difficult for these adolescents, and their quality of life is proportional to the freedom they can or cannot exercise.</p>
<h2>Eat well, exercise and visit your optometrist</h2>
<p>Type 1 diabetes is difficult to prevent, mainly because we don’t know all the reasons why it occurs and to proactively screen for it. The situation is different for Type 2 diabetes, which is strongly associated with unhealthy lifestyle in young people. Eating a healthy diet, exercising regularly, and combating sedentary lifestyles, including limiting screen leisure time (to less than two hours per day), are good ways to avoid or delay the onset of diabetes in young people. Screen time is also associated with <a href="https://pubmed.ncbi.nlm.nih.gov/28288985/">insulin resistance</a> and <a href="https://pubmed.ncbi.nlm.nih.gov/31270831/">obesity</a> in young people. In other words, healthy lifestyles must be encouraged and especially shared within the family unit.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/500780/original/file-20221213-16037-bsk51g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="young children ride bikes" src="https://images.theconversation.com/files/500780/original/file-20221213-16037-bsk51g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500780/original/file-20221213-16037-bsk51g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500780/original/file-20221213-16037-bsk51g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500780/original/file-20221213-16037-bsk51g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500780/original/file-20221213-16037-bsk51g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500780/original/file-20221213-16037-bsk51g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500780/original/file-20221213-16037-bsk51g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Healthy habits are good ways to avoid or delay the onset of diabetes in young people.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<p>As far as eyes are concerned, regular visits to the optometrist or ophthalmologist can detect early signs of diabetic complications <a href="https://guidelines.diabetes.ca/cpg/chapter30">(signs are seen in up to 30 per cent of patients shortly after diagnosis)</a>. These health professionals can also detect other oculo-visual problems arising from the disease, such as <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2518369/">loss of ability to focus up close (accommodation), partial paralysis of certain muscles of the eye resulting in double vision, delayed healing of surface corneal changes, dry eye or glaucoma</a>. Testing should be done <a href="https://guidelines.diabetes.ca/cpg/chapter30">at the time of medical diagnosis of diabetes</a>, or in anyone with a high-risk profile (heredity, obesity, sedentary lifestyle).</p>
<p>Since healthy lifestyle habits are an integral part of the treatment of the disease, it is not too late for Karl to enjoy a happier future. But it is important not to neglect regular follow-ups by his medical doctor and frequent visits to his family optometrist.</p><img src="https://counter.theconversation.com/content/196634/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Langis Michaud ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>The risk of developing eye complications is high in young people with Type 2 diabetes, which is increasingly affecting children and adolescents, especially those who are more sedentary.Langis Michaud, Professeur Titulaire. École d'optométrie. Expertise en santé oculaire et usage des lentilles cornéennes spécialisées, Université de MontréalLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1969202022-12-21T13:42:42Z2022-12-21T13:42:42ZReindeer eyes change color, putting Rudolph’s red nose in the shade – new research podcast<figure><img src="https://images.theconversation.com/files/502245/original/file-20221220-22-ecence.jpg?ixlib=rb-1.1.0&rect=562%2C1059%2C2994%2C1934&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Reindeer have adapted to the dim, blue light of the Arctic winter.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Reindeer_in_Winter_-_geograph.org.uk_-_3371243.jpg#/media/File:Reindeer_in_Winter_-_geograph.org.uk_-_3371243.jpg">Alice/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Reindeer noses may not glow red, but these creatures of cold climes have evolved the ability to change the color of their eyes to help them thrive in dark, northern winters. In this Discovery episode, we speak with <a href="https://scholar.google.com/citations?user=UYlObKkAAAAJ&hl=en&oi=ao">Glen Jeffery</a>, a professor of neuroscience at the Institute of Opthamology at UCL (University College London) in the U.K. about what makes reindeer eyes truly unique in the animal kingdom. </p>
<iframe src="https://embed.acast.com/60087127b9687759d637bade/63a1af7253df78001130274d" frameborder="0" width="100%" height="190px"></iframe>
<p><iframe id="tc-infographic-561" class="tc-infographic" height="100" src="https://cdn.theconversation.com/infographics/561/4fbbd099d631750693d02bac632430b71b37cd5f/site/index.html" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Most people have seen the gold, glowing eyes of a cat, a raccoon or some other nocturnal animal staring back at them during a nighttime drive. The part of the eye that produces that golden reflection, as Jeffery explains, “is a mirror that lots of animals have called the tapetum lucidum.” A taptetum helps animals see better in the dark by bouncing light from the back of the eye through the retina a second time. In most mammals, the tapetum is a “standard golden,” as Jeffery describes the color, and that color doesn’t change.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/502246/original/file-20221220-12-k4w2js.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A photo of a raccoon with glowing, gold eyes." src="https://images.theconversation.com/files/502246/original/file-20221220-12-k4w2js.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/502246/original/file-20221220-12-k4w2js.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=514&fit=crop&dpr=1 600w, https://images.theconversation.com/files/502246/original/file-20221220-12-k4w2js.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=514&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/502246/original/file-20221220-12-k4w2js.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=514&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/502246/original/file-20221220-12-k4w2js.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=645&fit=crop&dpr=1 754w, https://images.theconversation.com/files/502246/original/file-20221220-12-k4w2js.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=645&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/502246/original/file-20221220-12-k4w2js.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=645&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Many animals’ eyes shine in the darkness because of a reflective layer called the tapetum lucidum that is usually gold.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Raccoon_red_eye.JPG#/media/File:Raccoon_red_eye.JPG">Bowlhover/Wikimedia Commons</a></span>
</figcaption>
</figure>
<p>One day, Jeffery received a box in the mail out of the blue. It contained two jars filled with reindeer eyes from a slaughterhouse in Norway. One jar was labeled summer and one was labeled winter.</p>
<p>“I opened up the summer ones first and I thought, ‘I’m wasting my time here,’” says Jeffery. He saw golden eyes, just what he expected.</p>
<p>“But then we opened up the other eyes, and that was when there was a shock, because the winter eyes were blue,” he said. “I’d never seen anything like that in my life.”</p>
<p>Jeffery and his colleagues spent years studying the biology of reindeer eyes and the environment they are made for – the dim, blue-hued months of the Arctic winter. What they discovered is a marvelous bit of evolution that has given reindeer some of the most interesting eyes on Earth. Listen to this Discovery episode of the Conversation to hear about how Jeffery and his colleagues study reindeer eyes, why winter eyes are such a unique color and how light pollution can alter this finely tuned adaptation.</p>
<hr>
<p>This episode was written and produced by Katie Flood with Gemma Ware and hosted by Dan Merino. Eloise Stevens does our sound design, and our theme music is by Neeta Sarl.</p>
<p>You can find us on Twitter <a href="https://twitter.com/TC_Audio">@TC_Audio</a>, on Instagram at <a href="https://www.instagram.com/theconversationdotcom/">theconversationdotcom</a> or <a href="mailto:podcast@theconversation.com">via email</a>. You can also sign up to The Conversation’s <a href="https://theconversation.com/newsletter">free daily email here</a>. A transcript of this episode is <a href="https://cdn.theconversation.com/static_files/files/2795/Discovery_Ep3_Reindeer_Eyes_Transcript.pdf?1694453126">now available</a>.</p>
<p>Listen to “The Conversation Weekly” via any of the apps listed above, download it directly via our <a href="https://feeds.acast.com/public/shows/60087127b9687759d637bade">RSS feed</a> or find out <a href="https://theconversation.com/how-to-listen-to-the-conversations-podcasts-154131">how else to listen here</a>.</p><img src="https://counter.theconversation.com/content/196920/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Glen Jeffery receives funding from the Biotechnology and Biological Sciences Research Council of the UK.</span></em></p>In winter, light in the northern latitudes is dim and very blue compared to summer light. Reindeer eyes have evolved to be better suited at seeing in this unique environment.Daniel Merino, Associate Science Editor & Co-Host of The Conversation Weekly Podcast, The ConversationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1931922022-10-25T20:22:51Z2022-10-25T20:22:51ZDevelopment of vision in early childhood: No screens before age two<figure><img src="https://images.theconversation.com/files/491691/original/file-20221025-22-wx4aqi.jpg?ixlib=rb-1.1.0&rect=14%2C7%2C979%2C655&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Electronic devices are not, in and of themselves, a source of visual problems. Using these devices inappropriately can interfere with the natural development of the eye, as well as reading and learning skills. </span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Things are busy on a rainy Saturday afternoon when I make a trip to the mall to finalize some back-to-school shopping. I pass by a lot of people, including several parents with young children under two years old, in strollers, and am struck by the fact that all of the children have a tablet or phone in their hands. Has technology become the ultimate tool for keeping children calm?</p>
<p>As an optometrist and eye health expert, this observation saddens me every time I see it, since I know all the harmful effects such exposure to electronic tools can have on children.</p>
<p>These effects are all the more critical during the first years of life, both on the <a href="https://pubmed.ncbi.nlm.nih.gov/34625399/">visual level</a> and on the <a href="https://pubmed.ncbi.nlm.nih.gov/36190219/">cognitive and social development of children</a>.</p>
<h2>Visual development of children</h2>
<p>The human eye develops <a href="https://www.nationwidechildrens.org/family-resources-education/health-wellness-and-safety-resources/helping-hands/infant-vision-birth-to-one-year">through stimulation</a>. The quality of the optical stimulus influences the growth of the eyeball via a complex and balanced mechanism. At birth, the eye is hyperopic, that is to say, its power is not perfectly adjusted to its size. A child sees at short distances and is barely able to distinguish a shadow when grandpa comes to the bedroom door.</p>
<p>In the first few weeks, the eye grows, the retina matures and a balance is established between the growth of the eyeball and the power of the inner lens. At six months of age, each of the toddler’s two eyes has the vision of an adult eye. From this moment on, the eyes will develop their coordination, in order to generate vision in three dimensions. It’s also starting at the age of six months that the communication between the eyes develops in the visual brain as well.</p>
<p>Billions of neurological connections will have to be made during the <a href="https://opto.umontreal.ca/clinique/pdf/EFFETS%20DES%20ECRANS%20SUR%20LE%20D%C3%89VELOPPEMENT%20VISUEL%20DES%20ENFANTS.pdf">first eight years of life</a>. This maturation time is long, but necessary, considering that <a href="https://www.sciencedirect.com/science/article/pii/S0149763413001917">more than a third of the brain’s neurons are dedicated to vision</a>.</p>
<h2>A question of distance</h2>
<p>Electronic devices are not, in themselves, a source of visual problems. Rather, the inappropriate use of these devices can interfere with the natural development of the eye, as well as reading and learning skills.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/489407/original/file-20221012-17-g43eu3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two small children with glasses sitting on white chairs : a boy with a tablet computer, a girl with a cell phone" src="https://images.theconversation.com/files/489407/original/file-20221012-17-g43eu3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/489407/original/file-20221012-17-g43eu3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/489407/original/file-20221012-17-g43eu3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/489407/original/file-20221012-17-g43eu3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/489407/original/file-20221012-17-g43eu3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/489407/original/file-20221012-17-g43eu3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/489407/original/file-20221012-17-g43eu3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">For normal visual development, it is recommended that exposure to electronic devices be avoided between the ages of zero and two years.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<p>The first thing to consider is viewing distance. The eye is designed to look at a near distance that is about equal to the length of the forearm (distance from the elbow to the fingertips of the hand). That means about <a href="https://www.sciencedirect.com/science/article/pii/S0042698913000795">30 cm for a young child, and 40 cm for an adult</a>. However, tablets and phones are held on average 20-30 cm from the eye, and this distance <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/cxo.12453">becomes shorter with prolonged exposure</a>. The visual effort required to maintain a clear image at this distance is therefore doubled.</p>
<p>A distance that is too short influences the quality of the retinal image (and therefore visual development) and causes <a href="https://books.google.ca/books?hl=fr&lr=&id=jGGROHBFYt8C">excessive eye fatigue</a>. It is also important to understand that when eyes must accommodate short distances, they automatically converge towards the nose in order to focus at the normal reading distance. Too much effort spent accommodating the short distance is therefore accompanied by a greater than normal convergence. As the eye cannot maintain this prolonged effort over a long period of time, it will relax its effort and the perceived image will become blurred for a while, a sensory penalty that we want to avoid. After a period of rest, the eye will resume its effort, and this alternation between the clearness and the blur will continue as long as attention to the close image is required. So, ideally, the tablet or phone should always be kept at the distance of the forearm.</p>
<h2>Constant stimulation is not recommended</h2>
<p>The use of electronic tools, with games or videos, requires a constant attention span, without breaks. This is the second factor to consider. When a child draws in a notebook or reads a paper book, he or she will instinctively stop at some point, look elsewhere, far away, and become interested in something else around them. These pauses and breaks are beneficial <a href="https://www.aoa.org/healthy-eyes/eye-and-vision-conditions/computer-vision-syndrome?sso=y">for the visual system to recover from its effort</a>. Focusing on targets at a distance is also beneficial to the child’s visual development. With electronic tablets, it is not uncommon to see children doing sessions of more than two to three hours continuously, without looking up from the screen.</p>
<p>The visual apparatus of children from zero to two years old is simply not sufficiently developed and robust to undergo such stress from constant stimulation in front of the screen. In particular, the structural elements of the sclera (the deep layer of the eye), which give the eye rigidity and determine its size, develop between zero and two years of age and then stabilize. The visual stimulus at these ages can interfere and therefore <a href="https://www.researchgate.net/publication/335108098_Scleral_structure_and_biomechanics">influence the development of visual defects and pathology in later life</a>.</p>
<p>It is also important to note that the screen can emit blue light. Children’s eyes do not filter these rays like those of an adult. This means that children are exposed to more blue light, which may stimulate nearsightedness and disrupt the secretion of melatonin, <a href="https://www.myopiainstitute.com/eye-care/how-blue-light-affects-your-vision-and-overall-health/">which regulates our biological clock</a>. This can disrupt the naps necessary for children of this age, as well as sleep during the night. Sleep loss can also lead to myopia.</p>
<h2>Let’s learn about electronics</h2>
<p>For normal visual development, it is therefore recommended to <a href="https://publications.aap.org/pediatrics/article/128/5/1040/30928/Media-Use-by-Children-Younger-Than-2-Years?_ga=2.208746386.1459529850.1665228699-655911314.1665228699?autologincheck=redirected?nfToken=00000000-0000-0000-0000-000000000000">avoid all exposure to electronic devices between the ages of zero and two</a>. The exception would be occasional video conversations, under the supervision of a parent, to say hello to a grandparent who lives far away, for a few minutes.</p>
<p>From the age of two years on, an hour of exposure per day can be considered, especially to consult educational sites, always accompanied by a parent or an educator.</p>
<p>When the visual system is mature, around the age of six to eight, exposure can be increased gradually, without exceeding two to three hours per day, with 10-minute breaks every hour. Electronic device use should be avoided during meals, family activities, and at least one hour before sleep.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/489410/original/file-20221012-24-ip7l62.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Young mother holding her cute, crying baby daughter, looking at a tablet during a virtual video call business or family meeting at a distance" src="https://images.theconversation.com/files/489410/original/file-20221012-24-ip7l62.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/489410/original/file-20221012-24-ip7l62.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/489410/original/file-20221012-24-ip7l62.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/489410/original/file-20221012-24-ip7l62.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/489410/original/file-20221012-24-ip7l62.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/489410/original/file-20221012-24-ip7l62.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/489410/original/file-20221012-24-ip7l62.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Rare video conversations, with parental supervision, to wave to a grandparent from a distance, for a few minutes, can be considered.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>Let’s play outside!</h2>
<p>The best advice for successful visual development is to encourage exposure to outdoor light for <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6678505/#:%7E:text=Each%20additional%20hour%20of%20daily,by%2013%25%20%5B23%5D.">at least one hour per day, ideally two hours</a>. We are talking about playing, walking, and activities that are done outside. The amount of light is then much greater than indoors, which would stimulate the production of dopamine, a chemical mediator essential to regulating the growth of the eye. This is the most effective way to prevent the onset of myopia in children.</p>
<p>It is also important to make sure that a child’s visual system is normal and developing naturally. Therefore, the first examination by an optometrist should be done at six months of age (to validate that the eye has normal optics and that there are no congenital defects), and then at three years of age to evaluate eye coordination. If everything is normal, the next examination will take place at five years of age, and annually thereafter, <a href="http://nada.ca/wp-content/uploads/2018/09/BK-ChildrenAndTheirVision-2018-EN.pdf">considering that vision can change rapidly</a>.</p>
<p>In the case of an abnormality, the earlier we intervene in the process, the easier it is to restore normal oculo-visual function, either by exercise or by optical means.</p>
<p>By following these recommendations for visual hygiene, we will protect children’s visual system and ensure their normal development.</p>
<p>And let’s not forget that the most beautiful screen in the world is nature! We should offer it to our children more often.</p><img src="https://counter.theconversation.com/content/193192/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Langis Michaud ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>The impact of using electronic devices is critical during the first years of life, both visually and on the cognitive and social development of the child.Langis Michaud, Professeur Titulaire. École d'optométrie. Expertise en santé oculaire et usage des lentilles cornéennes spécialisées, Université de MontréalLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1834132022-08-24T15:35:58Z2022-08-24T15:35:58ZCataracts: we’re working on eye drops to treat them so people don’t need surgery<figure><img src="https://images.theconversation.com/files/480563/original/file-20220823-25-kpi17p.jpg?ixlib=rb-1.1.0&rect=7%2C0%2C4996%2C3338&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/young-female-ophthalmologist-using-apparatus-632890571">Olena Yakobchuk/Shutterstock</a></span></figcaption></figure><p>Many years ago, I began my PhD with the firm resolve of finding a cure for cataracts – not in several years or decades, but within the duration of my PhD. Such was my enthusiasm and naivety. Decades later, though, that dream looks as if it might come true. </p>
<p>Cataracts are the result of a buildup of broken protein fragments within the eye lens. This buildup and clumping together of protein fragments severely reduce the transmission of light to the retina – making things appear blurry or misty. It is the cause of around <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1705965/?report=reader">43% of all blindness</a>.</p>
<p>Surgery to remove the clouded lens and replace it with an artificial one has so far been the only treatment available for cataracts. About <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1705965/">10 million cataract operations</a> are performed each year, globally. The procedure can be life-changing, but who would not want to avoid surgery if a less-invasive treatment was available? This is where sterol eye drops come into the picture. (Sterols are fat-like substances that occur in nature.)</p>
<p>My colleagues and I recently <a href="https://pubmed.ncbi.nlm.nih.gov/35575904/">conducted a study in mice</a> that showed promising and dramatic effects on cataracts after we applied a sterol compound to their eyes. When the compound was applied to one eye of 26 mice with cataracts, we found that 61% of the treated lenses showed an improvement in their refractive index gradient. This gradient is a measure of optical density and a vital component of image quality. The opacity of the lenses was reduced in 46% of the mice, as well.</p>
<p>However, the effects were not universal, suggesting that the same remedy may not apply to all cataracts (there are several types). </p>
<p>The compound we used had been tested before, but not for optics. Yet the optical quality of the lens is fundamental to light travelling unimpeded to the retina and hence to maintaining vision. </p>
<p>Investigations using this sterol compound <a href="https://www.science.org/doi/10.1126/science.aac9145">reported in 2015</a> improved transparency in mouse lenses, and partially restored protein solubility both in the lenses of living mice and in human lenses in a dish.</p>
<p>But a subsequent <a href="https://www.nature.com/articles/s41598-019-44676-4">study in 2019</a> could not find evidence that this compound reverses protein buildup in rat and human samples, nor that it reverses the opacities in rat lenses with cataracts. However, the sterol compound had not been tested on whole, intact human lenses. And most importantly, the effect of this compound on the optical property of the refractive index (that is, the optical quality of the lens) had not been measured. </p>
<h2>Measuring optical quality</h2>
<p>I have spent years developing and applying methods of measuring the optical quality of the lens, and have been measuring lens optics for over a decade using the most advanced system in the world, the <a href="https://en.wikipedia.org/wiki/SPring-8">SPring-8 synchrotron</a> in Japan – a particle accelerator that produces powerful X-rays, allowing measurements to be taken with the highest accuracy yet on optical properties of the eye. </p>
<p>This technology has allowed my colleagues and me to accurately characterise the refractive index gradient in transparent lenses as well as those that have cataracts – something that could not be conducted using a visible light source. </p>
<p>The refractive index gradient is important for image quality because it provides improved focusing capacity. Cataracts disrupt this gradient because of the protein buildup. The application of X-ray measurements has been key to our latest findings. In addition, when we measure optical properties, we do this on whole lenses with the protein distributions left undisturbed in the lens. </p>
<p>The link between a lens’s optical function and the protein solubility and propensity to clump needs to be studied further. This is important for addressing whether it is possible to reverse the process of cataract formation and restore transparency to a clouded lens. </p>
<p>Scientists have long believed that a buildup of the major structural proteins of a cataract – the crystallins – is irreversible. So any possible treatment for a cataract could, at best, halt or slow its progression. </p>
<p>If this is not true and protein aggregation is reversible, then it opens up a wealth of treatment possibilities. Not only can cataracts be prevented by avoiding certain known causes, such as <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4097885/">poor nutrition</a>, <a href="https://iovs.arvojournals.org/article.aspx?articleid=2128544">smoking</a> and certain drugs, <a href="https://journals.lww.com/ijo/Fulltext/2014/62020/Etiopathogenesis_of_cataract__An_appraisal.2.aspx">such as steroids</a>, it may be possible to use drugs that prevent further progression. Other drugs may even be able to reverse the process of cataract formation and restore clarity to a lens that has become clouded.</p>
<p>Further research needs to include investigations of all proteins in the lens: the major structural proteins of the lens (the crystallins and the water channel proteins) in tandem with studies of optical function. </p>
<p>We are currently looking at the optics of the lens from all aspects, from early developmental stages to adulthood, and looking at how these results map on to changes in proteins.</p>
<p>A great deal more research may be needed, but what our recent research findings have shown is that non-surgical treatment for cataracts is possible – and may be closer than we think.</p><img src="https://counter.theconversation.com/content/183413/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Barbara Pierscionek currently receives funding from EU under the Marie Skłodowska-Curie Doctoral Training Centre scheme. </span></em></p>Eye drops might one day be a safe, non-invasive and less costly alternative to cataract surgery.Barbara Pierscionek, Professor and Deputy Dean, Research and Innovation, Anglia Ruskin UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1870512022-08-17T12:38:53Z2022-08-17T12:38:53ZFlies evade your swatting thanks to sophisticated vision and neural shortcuts<figure><img src="https://images.theconversation.com/files/478807/original/file-20220811-20-9x44dv.jpg?ixlib=rb-1.1.0&rect=22%2C29%2C4966%2C3485&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Fly brains can process images very quickly.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/house-fly-royalty-free-image/535501923">www.shutterexperiments.com/Moment via GettyImages</a></span></figcaption></figure><p>Sitting outside on a summer evening always sounds relaxing until flies and mosquitoes arrive – then the swatting begins. Despite their minuscule eyes and a <a href="https://www.fruitflybrain.org/#/">brain</a> roughly <a href="https://www.hhmi.org/news/complete-fly-brain-imaged-at-nanoscale-resolution">1 million times</a> smaller than yours, flies can evade almost every swat. </p>
<p>Flies can thank their fast, sophisticated eyesight and some neural quirks for their ability to escape swats with such speed and agility.</p>
<p><a href="https://scholar.google.com/citations?hl=en&user=4i4wRGgAAAAJ">Our lab</a> <a href="https://scholar.google.com/citations?user=WBxN0p4AAAAJ&hl=en&oi=ao">investigates insect flight and vision</a>, with the goal of finding out how such tiny creatures can process visual information to perform challenging behaviors, such as escaping your swatter so quickly.</p>
<h2>Faster vision</h2>
<p>Flies have compound eyes. Rather than collecting light through a single lens that makes the whole image – the strategy of human eyes – flies form images built from multiple <a href="https://doi.org/10.1007/978-3-642-74082-4_3">facets</a>, lots of individual lenses that focus incoming light onto clusters of photoreceptors, the light-sensing cells in their eyes. Essentially, each facet produces an individual pixel of the fly’s vision. </p>
<p>A fly’s world is fairly low resolution, because small heads can house only a limited number of facets – usually <a href="https://www.jstor.org/stable/24954051">hundreds to thousands</a> – and there is no easy way to sharpen their blurry vision up to the millions of pixels people effectively see. But despite this coarse resolution, flies see and process fast movements very quickly.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An illustration of a fly eye, showing tiny hexagonal facets and the photoreceptor layer under these facets." src="https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=378&fit=crop&dpr=1 600w, https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=378&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=378&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=475&fit=crop&dpr=1 754w, https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=475&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/478805/original/file-20220811-23-9ejxvf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=475&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Tiny hexagonal ‘facets’ take in light, and the photoreceptors beneath them process it in quick flashes.</span>
<span class="attribution"><a class="source" href="https://www.epfl.ch/labs/lis/research/completed/curvace/">Ecole Polytechnique Fédérale de Lausanne, Switzerland</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>We can infer how animals perceive fast movement from how quickly their photoreceptors can process light. Humans discern a maximum of <a href="https://www.mdpi.com/1648-9144/57/10/1096/htm">about 60 discrete flashes</a> of light per second. Any faster usually appears as steady light. The ability to see discrete flashes depends on the lighting conditions and which part of the retina you use. </p>
<p>Some LED lights, for example, emit discrete flashes of light quickly enough that they appear as steady light to humans – unless you turn your head. In your peripheral vision you may notice a flicker. That’s because your peripheral vision processes light more quickly, but at a lower resolution, like fly vision. </p>
<p>Remarkably, some flies can see as many as <a href="https://doi.org/10.2307/1539540">250 flashes per second</a>, around four times more flashes per second than people can perceive. </p>
<p>If you took one of these flies to the cineplex, the smooth movie you watched made up of 24 frames per second would, to the fly, appear as a series of static images, like a slide show. But this fast vision allows it to react quickly to prey, obstacles, competitors and your attempts at swatting.</p>
<p><a href="https://faculty.fiu.edu/%7Etheobald/">Our research</a> shows that flies <a href="https://doi.org/10.1016/j.visres.2020.02.007">in dim light lose some ability to see fast movements</a>. This might sound like a good opportunity to swat them, but humans also lose their ability to see quick, sharp features in the dark. So you may be just as handicapped your target. </p>
<p>When they do fly in the dark, flies and mosquitoes <a href="https://doi.org/10.1016/j.cub.2022.01.078">fly erratically</a>, with twisty flight paths to escape swats. They can also rely on <a href="https://doi.org/10.1016/bs.aiip.2016.04.007">nonvisual cues</a>, such as information from small hairs on their body that sense changes in the air currents when you move to strike.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/9wqZ7Jt3thg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Flight of a mosquito. Source: Intellectual Ventures.</span></figcaption>
</figure>
<h2>Neural tricks</h2>
<p>But why do flies see more slowly in the dark? You may have noticed your own vision becoming sluggish and blurry in the dark, and much less colorful. The process is similar for insects. Low light means <a href="https://doi.org/10.1098/rstb.2016.0062">fewer photons</a>, and just like cameras and telescopes, eyes depend on photons to make images. </p>
<p>But unlike a nice camera, which allows you to switch to a larger lens and gather more photons in dark settings, animals can’t swap out the optics of their eyes. Instead, they rely on <a href="https://doi.org/10.1016/S0042-6989(98)00262-4">summation</a>, a neural strategy that adds together the inputs of neighboring pixels, or increases the time they sample photons, to form an image.</p>
<p>Big pixels and longer exposures capture more photons, <a href="https://faculty.fiu.edu/%7Etheobald/visual-pooling/">but at the cost of sharp images</a>. Summation is equivalent to taking photographs with grainy film (higher ISO) or slow shutter speeds, which produce blurrier images, but avoid <a href="https://www.youtube.com/watch?v=eAhEatlueXA">underexposing</a> your subjects. Flies, <a href="https://doi.org/10.1016/j.visres.2018.05.007">especially small ones</a>, can’t see quickly in the dark because, in a sense, they are waiting for enough photons to arrive until they are sure of what they are seeing.</p>
<h2>Flight maneuverability</h2>
<p>In addition to rapidly perceiving looming threats, flies need to be able to fly away in a split second. This requires preparation for takeoff and <a href="https://doi.org/10.1126/science.1248955">quick flight maneuvers</a>. After visually detecting a looming threat, fruit flies, for example, adjust their posture in <a href="https://doi.org/10.1016/j.cub.2008.07.094">one-fifth of a second</a> before takeoff. Predatory flies, such as <a href="https://doi.org/10.1159/000435944">killer flies</a>, coordinate their legs, wings and halteres – dumbbell-shaped remnants of wings used for sensing in-air rotations – to quickly catch their prey midflight. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/tkK63pHFML0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Flight of a fly. Notice how they adjust their posture before takeoff. Source: The New York Times.</span></figcaption>
</figure>
<h2>How best to swat a fly</h2>
<p>To outmaneuver a fly, you must strike faster than it can detect your approaching hand. With practice, you may improve at this, but flies have honed their escapes over hundreds of millions of years. So instead of swatting, using other ways to manage flies, such as installing fly traps and cleaning backyards, is a better bet. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/OEIk_68miZc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Escape behavior of a fly in slow motion. Source: Florian Muijres et al, 2014 Science.</span></figcaption>
</figure>
<p>You can lure certain flies into a narrow neck bottle filled with apple cider vinegar and beer. Placing a funnel in the bottle neck makes it easy for them to enter, but difficult to escape. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A simple home-made fruit fly trap" src="https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=854&fit=crop&dpr=1 600w, https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=854&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=854&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1074&fit=crop&dpr=1 754w, https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1074&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/478976/original/file-20220812-1219-4t7yzv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1074&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Apple cider vinegar and beer trap to control fruit flies in your kitchen or backyard.</span>
<span class="attribution"><span class="source">Ravindra Palavalli-Nettimi</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>As for mosquitoes, some commercial repellents may work, but removing stagnant water around the house – in some plants, pots or any open containers – will help <a href="https://www.cdc.gov/mosquitoes/mosquito-control/athome/outside-your-home/index.html">eliminate their egg-laying sites</a> and reduce the number of mosquitoes around from the start. Avoid insecticides, as they also <a href="https://environment-review.yale.edu/deadlier-intended-pesticides-might-be-killing-beneficial-insects-beyond-their-targets-0">harm useful insects</a> such as bees and butterflies.</p><img src="https://counter.theconversation.com/content/187051/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jamie Theobald receives funding from the National Science Foundation (IOS-1750833). </span></em></p><p class="fine-print"><em><span>Ravindra Palavalli-Nettimi does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Why is it so difficult to swat a fly? A team of insect experts explains how a fly’s sophisticated vision allows it to quickly react to visual cues.Jamie Theobald, Associate Professor of Biological Sciences, Florida International UniversityRavindra Palavalli-Nettimi, Postdoctoral Research Associate, Florida International UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1824412022-08-01T15:29:08Z2022-08-01T15:29:08ZThe tongue: how one of the body’s most sensitive organs is helping blind people ‘see’<figure><img src="https://images.theconversation.com/files/464768/original/file-20220523-26-5xzgxc.jpg?ixlib=rb-1.1.0&rect=165%2C0%2C6312%2C4292&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The tip of the tongue is more sensitive than our fingertips.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/pretty-joyful-african-american-cute-short-2032746725">Anatoliy Karlyuk/Shutterstock</a></span></figcaption></figure><p>Ever wondered why kissing feels better than holding hands? The tongue is a pretty incredible piece of kit, though notoriously difficult to study, due to its position inside the mouth. Obviously, it gives us access to the wonderful world of taste, but more than that, it has greater sensitivity to touch than the fingertip. Without it, we aren’t able to speak, sing, breathe efficiently or swallow delicious beverages. </p>
<p>So why don’t we use it even more? <a href="https://doi.org/10.1037/xhp0001007">My new study</a> investigates how to make the most of this strange organ – potentially as an interface to help people with visual impairments navigate and even exercise. I realise this may sound mindboggling, but please bear with me.</p>
<p>My research is part of a field known as “sensory substitution”, a branch of interdisciplinary science that combines psychology, neuroscience, computer science and engineering to develop “sensory substitution devices” (known as SSDs). SSDs convert sensory information from one sense to another. For example, if the device is designed for a person with a visual impairment, this typically means converting visual information from a video feed into sound or touch. </p>
<h2>Drawing pictures on the tongue</h2>
<p><a href="https://www.researchgate.net/publication/7384990_Brainport_An_alternative_input_to_the_brain">BrainPort</a>, first developed in 1998, is one such technology. It converts a camera’s video feed into moving patterns of electrical stimulation on the surface of the tongue. The “tongue display” (a small device shaped like a lollipop) consists of 400 tiny electrodes, with each electrode corresponding to a pixel from a camera’s video feed. </p>
<p>It creates a low-resolution tactile display on the tongue matching the output from the camera. The technology can be used to help stroke victims maintain their sense of balance. And in 2015, the US Food and Drug Administration approved its use as an <a href="https://www.washingtonpost.com/news/to-your-health/wp/2015/06/18/fda-approves-device-to-help-blind-people-see-by-using-their-tongues/">aid for the visually impaired</a>.</p>
<p>Imagine holding your hand up to a camera and feeling a tiny hand simultaneously appear on the tip of your tongue. It sort of feels a bit like someone is drawing images on your tongue in popping candy. </p>
<p>While the BrainPort has been around for years, it hasn’t seen much real-world uptake, despite being ten times cheaper than a retinal implant. I use the BrainPort to test how human attention works on the surface of the tongue, to see if differences in perception might be the cause of this. </p>
<p>In psychology research, there is a famous method to test attention, called the <a href="https://jov.arvojournals.org/article.aspx?articleid=2121543">Posner Cueing paradigm</a>, named after the American psychologist <a href="https://www.apa.org/monitor/2009/12/posner">Mike Posner</a> who developed it in the 1980s to measure visual attention. </p>
<p>When I say attention, I don’t mean “attention span”. Attention refers to the set of processes that bring things from the environment into our conscious awareness. Posner found that our attention can be cued by visual stimuli. </p>
<p>If we briefly see something moving out of the corner of our eye, attention focuses on that area. We probably evolved this way to quickly react to dangerous snakes lurking around corners and in the edges of our visual field. </p>
<p>This process also occurs between senses. If you’ve ever sat in a pub garden in summer and heard the dreaded drone of an incoming wasp to one ear, your attention is very quickly drawn to that side of your body. </p>
<p>The sound of the wasp captures your auditory attention to the general location of the potentially incoming wasp so that the brain can quickly allocate visual attention to identify the exact location of the wasp, and tactile attention to quickly swat or duck away from the wasp. </p>
<p>This is what we call <a href="https://www.sciencedirect.com/science/article/pii/S1364661398011887">“cross-modal” attention</a> (vision is one mode of sensation, audio another): things that appear in one sense can influence other senses.</p>
<h2>Paying attention to the tongue</h2>
<p>My colleagues and I developed a variation of the Posner Cueing paradigm to see if the brain can allocate tactile attention on the surface of the tongue in the same way as the hands or other modes of attention. We know loads about visual attention, and tactile attention on the hands and other body parts, but have no idea if this knowledge translates to the tongue. </p>
<p>This is important because BrainPort is designed, built and sold to help people “see” through their tongue. But we need to understand if “seeing” with the tongue is the same as seeing with the eyes.</p>
<figure class="align-center ">
<img alt="Image of a blind man talking on the phone." src="https://images.theconversation.com/files/475826/original/file-20220725-18-zuoyzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/475826/original/file-20220725-18-zuoyzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/475826/original/file-20220725-18-zuoyzm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/475826/original/file-20220725-18-zuoyzm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/475826/original/file-20220725-18-zuoyzm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/475826/original/file-20220725-18-zuoyzm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/475826/original/file-20220725-18-zuoyzm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">How similar is seeing with the tongue to seeing with the eyes or hands?</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/young-blinded-man-using-phone-sending-1978517621">PH888/Shutterstock</a></span>
</figcaption>
</figure>
<p>The answer to these questions, like almost everything in life, is that it’s complicated. The tongue does respond to cued information in roughly the same way as the hands or vision, but despite the incredible sensitivity of the tongue, attentional processes are a bit limited compared with the other senses. It is very easy to over-stimulate the tongue – causing sensory overload that can make it hard to feel what’s going on.</p>
<p>We also found that attentional processes on the tongue can be influenced by sound. For example, if a BrainPort user hears a sound to the left they can more easily identify information on the left side of their tongue. This could help to guide attention and reduce sensory overload with the BrainPort if paired with an auditory interface. </p>
<p>In terms of real-world use of the BrainPort, this translates to managing the complexity of visual information that gets substituted and, if possible, use another sense to help share some of the sensory load. Using the BrainPort in isolation could be too overstimulating to provide reliable information and could potentially be improved by using other assistive technology alongside, such as the <a href="https://theconversation.com/blind-people-can-see-bodies-with-sound-study-24008">vOICe</a>. </p>
<p>We’re using these findings to develop a device to help rock climbers with visual impairments to <a href="https://dl.acm.org/doi/abs/10.1145/3491101.3519680">navigate while climbing</a>. To prevent information overload, we’re using machine learning to identify climbing holds and filter out less relevant information. We’re also exploring the possibility of using sound to cue where the next hold might be, and then use the feedback on the tongue to precisely locate the hold. </p>
<p>With a few tweaks, this technology may eventually become a more reliable instrument to help blind or deaf or blind people navigate. It may even help paraplegic people, unable to use their hands, navigate or communicate more efficiently.</p><img src="https://counter.theconversation.com/content/182441/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mike Richardson's PhD project was funded by the E.S.R.C. as part of a scholarship. He is also currently employed as a Research Associate at the University of Bath, where he is funded by MyWorld.</span></em></p>A device could be use to transmit a camera’s video feed into moving patterns of electrical stimulation on the surface of the tongue.Mike Richardson, Research Associate in Psychology, University of BathLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1807622022-05-05T12:43:20Z2022-05-05T12:43:20ZNew eye drops can help aging people see better – an optometrist explains how Vuity treats presbyopia<figure><img src="https://images.theconversation.com/files/461367/original/file-20220504-14-mcdrca.jpg?ixlib=rb-1.1.0&rect=55%2C132%2C7293%2C4759&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Nearly all people start to develop blurry vision once they hit their 40s and 50s.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/senior-woman-having-vision-problems-royalty-free-image/1319027194?adppopup=true">demaerre/iStock via Getty Images</a></span></figcaption></figure><p>When people get into their 40s and beyond, their close-up vision starts to worsen. For many people, cranking up the font size on a phone or maxing out the brightness on a computer is the only way to be able to read some text. </p>
<p>This condition is known as <a href="https://doi.org/10.3390/jcm11051385">presbyopia</a>, and it affects around <a href="https://dx.doi.org/10.2147%2FOPTH.S318065">128 million people</a> in the U.S. and more than a <a href="https://dx.doi.org/10.1097%2FAPO.0000000000000297">billion people worldwide</a>. </p>
<p>In late 2021, the U.S. Food and Drug Administration approved a new eye drop medication to treat presbyopia. As an <a href="https://ophthalmology.pitt.edu/people/robert-bittner-od-faao">optometrist</a>, I was initially skeptical. Prior to the release of these eye drops – <a href="https://news.abbvie.com/news/press-releases/us-food-and-drug-administration-approves-vuity-pilocarpine-hci-ophthalmic-solution-125-first-and-only-eye-drop-to-treat-presbyopia-age-related-blurry-near-vision.htm">called Vuity</a> – people would either need glasses, contacts or eye surgery to alleviate presbyopia. But after learning how these eye drops work, I recognized that for many people, they could offer an easier and safer way to see clearly again. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/461319/original/file-20220504-25-sehqkq.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram labelling the human eye." src="https://images.theconversation.com/files/461319/original/file-20220504-25-sehqkq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/461319/original/file-20220504-25-sehqkq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=439&fit=crop&dpr=1 600w, https://images.theconversation.com/files/461319/original/file-20220504-25-sehqkq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=439&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/461319/original/file-20220504-25-sehqkq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=439&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/461319/original/file-20220504-25-sehqkq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=552&fit=crop&dpr=1 754w, https://images.theconversation.com/files/461319/original/file-20220504-25-sehqkq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=552&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/461319/original/file-20220504-25-sehqkq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=552&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The pupil and lens are two of the most important parts of the eye involved in focusing on objects.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/eye-human-anatomy-royalty-free-illustration/478855654?adppopup=true">ttsz/iStock via Getty Images</a></span>
</figcaption>
</figure>
<h2>How eyes focus</h2>
<p>Many parts of the human eye interact with incoming light to produce a clear image.</p>
<p>The first thing light hits is the cornea, the clear outer layer that initially bends the light. Then light passes through the iris and pupil, which can shrink or grow to let more or less light into the inside of the eye. It then travels through the lens, which further bends the light and precisely focuses it onto the center of the retina. Finally, the light signal is transferred to the optic nerve at the back of the eye, for the brain to interpret as an image.</p>
<p>To produce a clear image, your eyes need to adjust to how far away an object is. Your eyes take three major steps <a href="https://www.ncbi.nlm.nih.gov/books/NBK542189/">to focus on objects</a> close to your face: your eyes point toward the object you want to look at, your lenses change shape and your pupils constrict. </p>
<p>Once you point your gaze at what you’re interested in, a small muscle in the eye contracts, which changes the shape of the lens to make it thicker. The thicker the lens is, the more the light bends as it passes through. At the same time, your pupils constrict to block some of the incoming light from other objects in the distance. When light bounces off an object and enters your eye, the rays of light at the center are what provide a clear image. Blocking the scattering light by constricting the pupil helps to sharpen the image of close objects.</p>
<p>You can simulate this process using a camera on your cellphone. First, point the camera at something in the distance. Then, move your thumb into the image, holding it about 6 inches away. Your thumb will start off blurry, but as the camera’s lens changes shape, your thumb will come into focus.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/461370/original/file-20220504-25-lthi7q.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing how the point of focus moves when a person has presbyopia." src="https://images.theconversation.com/files/461370/original/file-20220504-25-lthi7q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/461370/original/file-20220504-25-lthi7q.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/461370/original/file-20220504-25-lthi7q.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/461370/original/file-20220504-25-lthi7q.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/461370/original/file-20220504-25-lthi7q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/461370/original/file-20220504-25-lthi7q.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/461370/original/file-20220504-25-lthi7q.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Presbyopia stiffens the lens in the eye, and when a person can’t bend their lens as easily, they are unable to focus incoming light on the correct part of the retina and images appear blurry.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Presbyopia.png#/media/File:Presbyopia.png">BruceBlaus via WikimediaCommons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>What is presbyopia?</h2>
<p>Presbyopia is the inability of the eyes to focus on close objects, which results in blurry images. It <a href="https://doi.org/10.1016/S0042-6989(97)00102-8">begins when people are in their 40s</a> and progresses until it plateaus around the age of 60.</p>
<p>Researchers know that <a href="https://doi.org/10.1016/S0042-6989(97)00102-8">age is the main driver of presbyopia</a>, but there is an ongoing debate over the <a href="https://doi.org/10.1016/j.preteyeres.2004.11.001">mechanical causes at its root</a>.</p>
<p>One theory suggests that as lenses age, they <a href="https://doi.org/10.3928/1081597X-20170621-05">get heavier</a> and can’t change shape as easily. Another theory suggests that the <a href="https://doi.org/10.3928/1081597X-20170621-05">muscle that pull on the lens become weaker</a> with age. I suspect presbyopia likely occurs due to a combination of both. Regardless of the cause, the result is that when looking at close objects, people’s eyes are no longer able to bend incoming light enough to direct it at the center of the retina. Instead, the light is focused at a place behind the retina, resulting in blurry vision. </p>
<h2>How the eye drops work</h2>
<p>Remember, there are two major things an eye does to focus on close objects: the lens changes shape and the pupil gets smaller. Since presbyopia limits the ability of the lens to change shape, these eye drops <a href="https://doi.org/10.1007/s40123-022-00482-2">compensate by causing the pupil to get smaller</a>. Constricting the pupil reduces the amount of light scatter. This makes it so that the light entering the eye is better concentrated onto the retina, thus creating a wider range of distances where objects are in focus and allowing people to see both close and far objects clearly.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/461320/original/file-20220504-12-pummws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing different depths of field." src="https://images.theconversation.com/files/461320/original/file-20220504-12-pummws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/461320/original/file-20220504-12-pummws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=547&fit=crop&dpr=1 600w, https://images.theconversation.com/files/461320/original/file-20220504-12-pummws.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=547&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/461320/original/file-20220504-12-pummws.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=547&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/461320/original/file-20220504-12-pummws.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=687&fit=crop&dpr=1 754w, https://images.theconversation.com/files/461320/original/file-20220504-12-pummws.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=687&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/461320/original/file-20220504-12-pummws.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=687&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Making the pupil smaller and allowing less light into the eye increases depth of field, making closer objects appear in focus – as seen in diagram a above – compared to a larger pupil and narrower depth of field as seen in diagram b.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Depth-of-field.svg#/media/File:Depth-of-field.svg">MikeRun via WikimediaCommons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Once you put the drops in your eyes, it takes about 15 minutes for the active ingredient, pilocarpine, to begin working. Pilocarpine is a medication that was first discovered in the late 1800s, and can <a href="https://www.drugs.com/mtm/pilocarpine-ophthalmic.html">treat conditions such as glaucoma and ocular hypertension</a>. The effect on pupils lasts for about six hours.</p>
<p>Smaller pupils mean that less light gets into the eye. While this isn’t a problem during the day when there is a lot of sun, it can cause difficulty seeing in low-lighting conditions. Aside from these downsides, the most common side effects of the drops are headache and red eyes.</p>
<h2>Presbyopia in the future</h2>
<p>Vuity is currently approved for <a href="https://www.rxabbvie.com/pdf/vuity_pi.pdf">once-daily use</a> in each eye. A bottle will cost around $80, requires a prescription and will last for nearly a month if used daily. For some people, it could be a great alternative or adjunct to glasses or surgery. </p>
<p>While Vuity may be the first FDA-approved eye drops to treat presbyopia, researchers are studying a <a href="https://dx.doi.org/10.1016%2Fj.jcrs.2012.07.028">number of other approaches</a>. Some are developing eye drops that include <a href="https://dx.doi.org/10.1097%2FAPO.0000000000000297">non-steroidal anti-inflammatory drugs</a> to help constrict the pupil – similarly to Vuity. Other teams are studying drops that <a href="https://dx.doi.org/10.1097%2FAPO.0000000000000297">soften and reduce the weight of the lens</a> to promote easier focusing. Finally, some early research has shown that pulsed electrostimulation of eye muscles can help strengthen them and improve people’s ability to bend their lenses.</p>
<p>The future of presbyopia treatment is exciting as researchers work on many potential ways to overcome this universal condition of old age. For now, Vuity – while not a magic cure for everyone with presbyopia – is an innovative option and may be worth asking your eye doctor about.</p>
<p>[<em>Understand new developments in science, health and technology, each week.</em> <a href="https://memberservices.theconversation.com/newsletters/?nl=science&source=inline-science-understand">Subscribe to The Conversation’s science newsletter</a>.]</p><img src="https://counter.theconversation.com/content/180762/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Robert Bittner does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>As people age, their eyes lose the ability to focus on close objects. A new eye drop treatment called Vuity can improve vision without the need for glasses, contacts or surgery.Robert Bittner, Assistant Professor of Ophthalmology, University of PittsburghLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1795312022-04-11T12:14:59Z2022-04-11T12:14:59ZWhy do cats’ eyes glow in the dark?<figure><img src="https://images.theconversation.com/files/456935/original/file-20220407-12485-7gz53u.jpg?ixlib=rb-1.1.0&rect=1089%2C47%2C2904%2C1856&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The same thing that makes their eyes glow helps cats see better in dim light.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/portrait-of-cat-with-glowing-eyes-sitting-on-steps-royalty-free-image/640438733">Cletus Waldman/EyeEm via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Why do cats’ eyes glow in the dark? Chloe, age 10, Barkhamsted, Connecticut</strong></p>
</blockquote>
<hr>
<p>Cats and many other animals, <a href="https://doi.org/10.1111/j.1463-5224.2004.00318.x">including most dogs</a>, can <a href="https://doi.org/10.1111/j.1463-5224.2004.00318.x">reflect light from their eyes</a>. That’s why cats’ eyes will usually shine brightly in photos taken in a dimly lit room or glow when illuminated in the dark by a flashlight or a car’s headlights.</p>
<p>Species whose eyes glow have evolved to see better in low light because they either forage or need to look out for predators throughout the night, or they do most of their hunting at <a href="https://dickinsoncountyconservationboard.com/2018/06/26/not-nocturnal-crepuscular/">dawn and dusk</a>. In fact, domesticated cats can see in conditions that are only <a href="https://www.dvm360.com/view/vision-in-dogs-and-cats">16% as bright</a> as what people require.</p>
<p>Cats accomplish this because their pupils – the openings that appear black in the middle of their eyes that widen and narrow in response to light conditions – are special. Pupils operate like windows, with bigger ones letting more light into the eye. And a cat’s pupils can become <a href="https://www.dvm360.com/view/vision-in-dogs-and-cats">up to 50% larger</a> than human pupils in dim light. They also have a <a href="https://www.dvm360.com/view/vision-in-dogs-and-cats">higher number</a> of a specific type of light-sensing cell in the back of their eyes than we do. These cells, <a href="https://www.cis.rit.edu/people/faculty/montag/vandplite/pages/chap_9/ch9p1.html">called rods</a>, catch low-level light. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/457176/original/file-20220408-41073-5610vt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram of the eyes of a human, a lynx and a puma" src="https://images.theconversation.com/files/457176/original/file-20220408-41073-5610vt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/457176/original/file-20220408-41073-5610vt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=199&fit=crop&dpr=1 600w, https://images.theconversation.com/files/457176/original/file-20220408-41073-5610vt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=199&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/457176/original/file-20220408-41073-5610vt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=199&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/457176/original/file-20220408-41073-5610vt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=250&fit=crop&dpr=1 754w, https://images.theconversation.com/files/457176/original/file-20220408-41073-5610vt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=250&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/457176/original/file-20220408-41073-5610vt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=250&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Humans do not have a tapetum lucidum but cats, including lynxes and pumas, do.</span>
<span class="attribution"><a class="source" href="https://www.open.edu/openlearn/mod/oucontent/view.php?id=2225&extra=thumbnailfigure_idm46597346755312">The Open University</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>The tapetum lucidum</h2>
<p>In addition to having large pupils and lots of rods, cats have something people don’t: a tapetum lucidum, a Latin medical term that translates to “<a href="https://en.wiktionary.org/wiki/tapetum_lucidum">bright or shining tapestry</a>.” The tapetum lucidum is also known as “<a href="http://www.eyecareforanimals.com/conditions/eyeshine-veterinary/">eyeshine</a>.”</p>
<p>It’s located in the back of the eye behind the <a href="https://www.healthline.com/human-body-maps/retina#1">retina</a> – a thin layer of tissue that receives light, converts the light to an electrical signal and sends this signal to the brain to interpret the image.</p>
<p>A cat’s tapetum lucidum is made up of cells with crystals that, like a mirror, <a href="https://doi.org/10.1111/j.1463-5224.2004.00318.x">reflect light</a> back to the retina. This gives the retina a second chance to absorb more light.</p>
<p>The feline tapetum lucidum is special because its reflective compound is <a href="https://doi.org/10.1111/j.1439-0264.1990.tb00892.x">riboflavin</a>, a type of vitamin B. Riboflavin has unique properties that amplify light to a <a href="https://doi.org/10.1111/j.1439-0264.1990.tb00892.x">specific wavelength</a> that cats can see well, which greatly increases the sensitivity of the retina to low light.</p>
<p>In cats, the tapetum most often glows yellow-green or yellow-orange, but the color varies, just like their <a href="https://excitedcats.com/types-of-cat-eye-colors/">irises</a> – the colorful part of their eye, which can be <a href="https://excitedcats.com/types-of-cat-eye-colors/">green, yellow, blue or golden</a>. Variation in tapetum color is not unique to cats and can be found in <a href="https://doi.org/10.1111/j.1463-5224.2004.00318.x">lots of species</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/456944/original/file-20220407-10731-d1wffn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A dog with glowing eyes" src="https://images.theconversation.com/files/456944/original/file-20220407-10731-d1wffn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/456944/original/file-20220407-10731-d1wffn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/456944/original/file-20220407-10731-d1wffn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/456944/original/file-20220407-10731-d1wffn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/456944/original/file-20220407-10731-d1wffn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/456944/original/file-20220407-10731-d1wffn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/456944/original/file-20220407-10731-d1wffn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Most dogs’ eyes will glow in dark spaces when a light shines on them.</span>
<span class="attribution"><span class="source">Tommy Greco</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Other animals’ eyes glow too</h2>
<p>Many other animals that need to see at night have a tapetum lucidum. That includes predators and prey alike, everything from wild foxes to farmed <a href="https://www.merckvetmanual.com/eye-diseases-and-disorders/ophthalmology/ocular-fundus">sheep and goats</a>.</p>
<p>The tapetum lucidum is also useful to fish, <a href="https://seaworld.org/animals/all-about/bottlenose-dolphin/senses/">dolphins</a> and other aquatic animals, because it helps them see better in murky, dark water.</p>
<p>In land animals, the tapetum is found in the <a href="https://doi.org/10.1111/j.1463-5224.2004.00318.x">top half of the eye</a> behind the retina, because they need to see what is on the ground best. But in aquatic animals the <a href="https://doi.org/10.1111/j.1463-5224.2004.00318.x">tapetum takes up most of the eye</a>, because they need to see all around them in the dark.</p>
<p>Like cats, <a href="https://doi.org/10.1111/j.1439-0264.1990.tb00892.x">the lemur</a>, a small primate, and its close relative, the bush baby – also known as a “<a href="https://www.nationalgeographic.com/animals/mammals/facts/bushbabies?loggedin=true">night monkey</a>” – also have a superreflective tapetum made with riboflavin.</p>
<p>Even though a lot of animals have eyeshine, some small domesticated dogs lack this trait. Most animals with <a href="https://www.scientificamerican.com/article/why-do-dogs-get-blue-not/">blue eyes and white or light-colored coats</a> have also lost this trait.</p>
<p>So don’t be alarmed if your dog’s or cat’s eyes don’t glow. The list of other species <a href="https://doi.org/10.1111/j.1463-5224.2004.00318.x">without a tapetum lucidum</a> includes pigs, birds, reptiles and most rodents and primates – including humans. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/456689/original/file-20220406-26-jgsrin.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Bush babies' eyes glow" src="https://images.theconversation.com/files/456689/original/file-20220406-26-jgsrin.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/456689/original/file-20220406-26-jgsrin.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=462&fit=crop&dpr=1 600w, https://images.theconversation.com/files/456689/original/file-20220406-26-jgsrin.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=462&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/456689/original/file-20220406-26-jgsrin.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=462&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/456689/original/file-20220406-26-jgsrin.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=581&fit=crop&dpr=1 754w, https://images.theconversation.com/files/456689/original/file-20220406-26-jgsrin.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=581&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/456689/original/file-20220406-26-jgsrin.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=581&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This bush baby can probably see better at night than you can.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/bush-baby-illuminated-at-night-descending-from-a-royalty-free-image/1180488942">Smartshots International/Moment via Getty Images</a></span>
</figcaption>
</figure>
<h2>Is there a downside?</h2>
<p>Unfortunately, animals with a tapetum lucidum <a href="https://www.dvm360.com/view/vision-in-dogs-and-cats">sacrifice some visual acuity</a> for their ability to see in dim light.</p>
<p>That’s because all that light bouncing around as it reflects off the tapetum can make what they see a little fuzzier. So, a cat needs to be <a href="https://www.dvm360.com/view/vision-in-dogs-and-cats">seven times closer</a> to an object to see it as sharply as a person would in a brightly lit place.</p>
<p>But don’t worry, I’m sure your cat would rather see clearly at night than read a book.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p><img src="https://counter.theconversation.com/content/179531/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Braidee Foote does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>A veterinary ophthalmologist explains what’s going on.Braidee Foote, Clinical Assistant Professor of Veterinary Ophthalmology, University of TennesseeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1630252021-06-22T09:36:13Z2021-06-22T09:36:13ZPseudo-hallucinations: why some people see more vivid mental images than others – test yourself here<figure><img src="https://images.theconversation.com/files/407199/original/file-20210618-19-i2g5dv.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3600%2C2700&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The brain can see a lot of things that aren't there.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/will-universe-remember-me-series-design-1043312566">agsandrew/Shuttestock</a></span></figcaption></figure><p>Consider the statements below. What do they describe? A trip on psychedelics? A dream?</p>
<blockquote>
<p>I felt I could reach through the screen to get to another place.</p>
<p>Lasers became entire fans of light sweeping around, and then it felt as if the screen began to expand.</p>
<p>I saw old stone buildings … like a castle … I was flying above it.</p>
</blockquote>
<p>In reality, they are statements that different people reported after viewing the “Ganzflicker” on their computers – an intense full-screen, red-and-black flicker <a href="https://docs.google.com/forms/d/e/1FAIpQLSf7Fs5gzrcJDUx_75JkZu6xwyGzJ3N9BfyOm6AzOJtqw4Ae3w/viewform">that anyone can access online</a> and that we use in our experiments. In less than ten minutes, it creates altered states of consciousness, with no lasting effects for the brain. Visual experiences set in almost as soon as you start looking at it.</p>
<p>But our new study, <a href="https://www.sciencedirect.com/science/article/pii/S0010945221001957?casa_token=TOFWP0Boy3UAAAAA:ZcIk6kquOBS6l9kkRnrMF7ACWNAjRH-rk4Cj8wJtk3xTRrw9F4pRMRe-7z7fYKGECHFMueP86g">published in Cortex</a>, shows that while some people see castles or fractals in the Ganzflicker, others see nothing. We have come up with a theory of where those individual differences come from.</p>
<p>Like a computer screen, the part of your brain that processes visual information (the visual cortex) has a refresh “button” which helps it sample the environment – <a href="https://www.sciencedirect.com/science/article/pii/S1364661303000950?casa_token=NElyOuDSAmoAAAAA:ZKYNf8sLTefOlNYdcuVLMWkaRquJsKlTb76E_WNir_NID1FmbOdSOYmoP8AtWbYb1mUiGTRtrg">taking snapshots of the world</a> in quick succession. In other words, your brain collects sensory information with a certain frequency. Yet you see the world as continuous and dynamic, thanks to your brain’s sophisticated ability to fill in the blanks. </p>
<p>For example, your eyes have a blind spot right outside the centre of vision, but you don’t see a patch of blackness everywhere you look. Your visual cortex extrapolates from the surrounding visual information so that your whole field of view <a href="https://www.jneurosci.org/content/29/28/8960.full">appears to be complete</a>. If the sensory information being processed is the Ganzflicker, this will interact with your brain’s own rhythms to alter how you fill in or interpret what you are seeing. </p>
<p>Ganzflicker is known to elicit the experience of anomalous sensory information in the external environment, called pseudo-hallucinations. “Simple” experiences - like seeing lasers or illusory colours - have previously been explained as your brain reacting to <a href="https://www.sciencedirect.com/science/article/pii/S0010945208001433?casa_token=RdQEIvTi--QAAAAA:6oUwwzQF_-Rut7kuNmuX3tLXPztnKbaCYfBm4OHUI0brp_8GKMFwf0cI6hkDdwLepGsuf7MVxQ#bib87">clashes between Ganzflicker</a> and the brain’s rhythms. But how do some people see complex pseudo-hallucinations such as “old stone castles”?</p>
<h2>Capacity for mental images</h2>
<p>The brain is composed of many different regions interacting with each other, including “low-level” sensory regions and regions that correspond to “high-level” cognitive processes. Discriminating whether a line is vertical or horizontal, for example, is considered a low-level sensory process, whereas determining whether a face is friendly or annoyed is a high-level cognitive process. The latter is more open to interpretation.</p>
<p>Visual mental imagery, or the mental simulation of sensory information – the “mind’s eye” – is one of these high-level cognitive processes. High-level processes can interact with low-level processes to shape your brain’s interpretation of what you are seeing. If someone sees simple pseudo-hallucinations in the Ganzflicker, their brains may automatically interpret that information as more meaningful or realistic with help from their mind’s eye.</p>
<figure class="align-center ">
<img alt="Image of mannequins with blindfolds saying 'aphantasia'." src="https://images.theconversation.com/files/407202/original/file-20210618-16-1r1d5cp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/407202/original/file-20210618-16-1r1d5cp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=218&fit=crop&dpr=1 600w, https://images.theconversation.com/files/407202/original/file-20210618-16-1r1d5cp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=218&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/407202/original/file-20210618-16-1r1d5cp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=218&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/407202/original/file-20210618-16-1r1d5cp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=274&fit=crop&dpr=1 754w, https://images.theconversation.com/files/407202/original/file-20210618-16-1r1d5cp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=274&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/407202/original/file-20210618-16-1r1d5cp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=274&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Some people can’t see mental images.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/aphantasia-can-blind-our-views-limit-1932512699">GoodIdeas/Shutterstock</a></span>
</figcaption>
</figure>
<p>What most people don’t realise is that everyone’s imagery is different. Some people have imagery that is as vivid as actually seeing something in front of them. A small proportion of people have a “blind mind’s eye” and cannot even visualise the faces of their friends or family. This condition <a href="https://theconversation.com/aphantasia-explained-some-people-cant-form-mental-pictures-162445">is called aphantasia</a>, and has attracted an increasing amount of attention in the last few years. Many people are, of course, somewhere in between these extremes. </p>
<h2>The power of Ganzflicker</h2>
<p>It is very difficult to describe and compare imagery experiences, since they are private, internal, subjective events. But it turns out that the Ganzflicker can help.</p>
<p>We discovered that imagery ability can be reflected in an individual’s description of a ten-minute experience with Ganzflicker. Almost half of people with aphantasia see absolutely nothing in the Ganzflicker. The other half see mostly simple patterns like geometric shapes or illusory colours. Compare that to people with visual mental imagery, for whom the majority see meaningful complex objects, such as animals and faces. Some even see entire pseudo-hallucinatory environments, like a stormy beach or a medieval castle.</p>
<p>Going back to the idea of brain rhythms, it’s possible that people who see imagery have naturally lower-frequency rhythms in visual cortex - closer to the Ganzflicker frequency - which makes them susceptible to experiencing pseudo-hallucinations. People with aphantasia, on the other hand, have naturally higher-frequency rhythms in the visual cortex – which may give them a buffer against the effects of the Ganzflicker. </p>
<p>Our theory is that mental imagery and pseudo-hallucinations elicited by Ganzflicker are tapping into the same processes in the brain. This means that Ganzflicker captures a dynamic projection of people’s imagined experiences, like opening a window to the mind’s eye.</p>
<p>Ganzflicker is therefore a promising tool for understanding individual differences in mental imagery and its interaction with the visual environment. </p>
<p>The experiment can help people share their unique experiences with each other – ultimately bringing subjective experience into the real world.</p><img src="https://counter.theconversation.com/content/163025/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Reshanne Reeder received funding from the Leibniz Association (SAS-2015-LIN-LWC) to conduct this study.</span></em></p>Experiment that creates altered states of consciousness sheds light on an old problem.Reshanne Reeder, Senior Lecturer in Psychology, Edge Hill UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1606832021-06-01T16:39:57Z2021-06-01T16:39:57ZMacular degeneration is a leading cause of blindness. Here’s how to prevent it<figure><img src="https://images.theconversation.com/files/399869/original/file-20210510-18-1hk45fb.jpg?ixlib=rb-1.1.0&rect=2%2C0%2C1347%2C667&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Macular degeneration can result in blurred or no vision in the center of the visual field. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/">(Shutterstock)</a></span></figcaption></figure><p>Jacques was a very active retiree. That ended one November morning as his life was suddenly turned upside down. When he woke that day, he could not see out of one eye. Panicked, he came to see me right away. </p>
<p>Jacques had been diagnosed with age-related macular degeneration (AMD) a few years earlier. His condition had been stable, but now it suddenly progressed to the most severe form of the disease, “<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3404137/">wet degeneration</a>.” This stage is characterized by the sudden development of a network of new blood vessels that ooze into the deep layers of the retina, causing a rapid loss of functional vision in the affected eye.</p>
<p>An urgent referral to ophthalmology is made in cases like these because the window of opportunity for treatment is narrow. Immediate treatment usually results in <a href="https://www.aao.org/preferred-practice-pattern/age-related-macular-degeneration-ppp">the best prognosis</a>. Jacques managed to get treatment within a few days.</p>
<p>The ophthalmologist gave him <a href="https://www.cochrane.org/CD005139/EYES_anti-vascular-endothelial-growth-factor-neovascular-age-related-macular-degeneration">intraocular injections</a> of medication, but this only improved his vision slightly. Jacques was depressed and his anxiety was increasing. He felt useless and had lost considerable autonomy.</p>
<p>The loss of an eye is a traumatic event, regardless of the patient’s age. While the significant negative psychological effects are well documented for <a href="https://pubmed.ncbi.nlm.nih.gov/26893539/">older patients</a>, recent publications also report the same adverse consequences in <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5328297/">younger populations</a>.</p>
<p>For example, the rate of depression is six times greater in those with significant vision loss than in the general population (<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2792986/">25 per cent versus four per cent</a>).</p>
<h2>Hope for patients</h2>
<p>So what can we do to help Jacques? We can’t promise that his vision will be fully restored. Although injection treatments can be effective, the basic degeneration will not go away. The best option for Jacques is to refer him to a visual impairment rehabilitation centre where he will receive help from a variety of professionals.</p>
<p>At this centre, he will be seen by specialists trained to treat visual impairment and its repercussions on the lives of people who suffer from it, and on the people around them. Understanding this reality is the first step toward helping patients address their needs.</p>
<p>The next step, after providing psychological support to Jacques, is to optimize his visual condition. Optometrists who specialize in low vision can prescribe optical aids to help Jacques regain some of his visual function, including magnifiers, vision aids and specialized glasses that can be provided through a government program designed for this purpose.</p>
<p>Specialists in visual impairment rehabilitation (VIR) trained at the school of optometry of the University of Montréal (the only institution in Canada that offers a master’s program in VIR), can then help Jacques learn new strategies to carry out his daily activities. Specialized educators can help him to use a computer and specific software. When needed, orientation and mobility specialists teach people with visual impairments methods how to safely orient themselves and get around whether on the street or in an unfamiliar environment.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/391277/original/file-20210323-18-1nq7b4v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/391277/original/file-20210323-18-1nq7b4v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/391277/original/file-20210323-18-1nq7b4v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/391277/original/file-20210323-18-1nq7b4v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/391277/original/file-20210323-18-1nq7b4v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/391277/original/file-20210323-18-1nq7b4v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/391277/original/file-20210323-18-1nq7b4v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Age-related macular degeneration (AMD) can result in blurred or no vision in the centre of the visual field.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<p>A social worker, aware that the impacts of a visual handicap go far beyond the person experiencing it, will accompany Jacques during his rehabilitation process and communicate with his family. In short, Jacques will have a good support system and will be able to regain a certain level of autonomy in his life, which, in turn, will have a positive impact on his morale. <a href="http://www.aqdm.org/home.html">Support groups</a> can also help him in his efforts and if, thanks to effective injections, his visual acuity improves, he will be in a win-win situation.</p>
<p>However, Jacques still has other concerns about his disease. He is worried that his children will develop similar conditions, especially one of his sons.</p>
<h2>Several risk factors</h2>
<p>Age-related macular degeneration is aptly named: its prevalence increases with the age of the patients. Nearly one million Canadians — 300,000 in Québec alone — suffer from AMD. Of these, <a href="https://www.inesss.qc.ca/fileadmin/doc/INESSS/Rapports/DMLA/Note_informative_DMLA.pdf">10 to 15 per cent have the wet form</a>, like Jacques. AMD is the leading cause of blindness in people over the age of 65.</p>
<p>In addition to aging, other risk factors associated with the development of the disease include family history, ethnic origin (white people are more affected), gender (women are more affected), atherosclerotic and vascular diseases, obesity and sun exposure (phototoxicity of the retinal cells).</p>
<p>Smoking also plays an important role. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3866712/">Consuming 25 cigarettes per day</a> doubles the risk of severe damage. Exposure to second-hand smoke is also harmful. The chemicals absorbed during exposure to smoke <a href="https://pubmed.ncbi.nlm.nih.gov/30426163/">increase the absorption of harmful sunlight by the retina by 1,000 times</a>.</p>
<p>For Jacques’ son, the risk of developing AMD is clear but so are his options. He will not be able to change his genes, prevent himself from aging or change his ethnicity or chromosomes. However, he can control the modifiable factors: he can quit smoking, control his weight and stay physically active.</p>
<hr>
<p>
<em>
<strong>
À lire aussi :
<a href="https://theconversation.com/glaucoma-visions-silent-killer-113878">Glaucoma: Vision's silent killer</a>
</strong>
</em>
</p>
<hr>
<p>Diet can play a preventive role. Reducing fat intake in the diet and ensuring adequate omega-3 consumption (forms of triglyceride, 800 mg DHA/EPA per day) <a href="https://pubmed.ncbi.nlm.nih.gov/18779490/">are important</a>. However, adding vitamins formulated for eye health to the mix is not recommended in Jacques’ case. Vitamins are only effective in treating dry AMD in its middle stages, not for preventing it. However, they are one of the few ways Jacques can reduce the risk of having his other eye affected and losing all his functional vision.</p>
<p>It is imperative for both Jacques and his son to follow the doctor’s recommendations on managing vascular problems (hypertension, cholesterol, diabetes). When poorly controlled, these conditions significantly increase the risk of developing wet AMD.</p>
<p>Remember, macular degeneration is first and foremost a vascular disease: the blood vessels are no longer able to nourish the retinal cells and no longer get rid of their metabolic waste efficiently. As a result, the cells die. New blood vessels develop, but they are fragile and, when they break, flood the retina with fluid.</p>
<p>Finally, both father and son will need to protect themselves from the sun’s harmful rays, either with a transparent filter (UV400) in their regular prescription glasses or by wearing good quality sunglasses when they are outdoors. Their eye care professionals will be able to advise them about this.</p>
<p>Jacques’ spirits are not high, but I have given him some hope that better days lie ahead. He knows he can count on a team of professionals to support him and that he will not be dealing with his condition alone. There is hope. And hope is the first thing that makes it possible to overcome the impacts of any disease.</p><img src="https://counter.theconversation.com/content/160683/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Langis Michaud ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>Age-related macular degeneration (AMD) lives up to its name: Its prevalence increases with age and it is the leading cause of blindness in people over 65 years old.Langis Michaud, Professeur Titulaire. École d'optométrie. Expertise en santé oculaire et usage des lentilles cornéennes spécialisées, Université de MontréalLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1601522021-05-06T18:12:42Z2021-05-06T18:12:42ZNocturnal dinosaurs: Night vision and superb hearing in a small theropod suggest it was a moonlight predator<figure><img src="https://images.theconversation.com/files/398999/original/file-20210505-17-16fmhv4.png?ixlib=rb-1.1.0&rect=32%2C9%2C1511%2C788&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Fossils of _Shuvuuia deserti_ depict a small predatory creature with exceptional night vision and hearing.</span> <span class="attribution"><span class="source">Mick Ellison/American Natural History Museum</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Today, barn owls, bats, leopards and many other animals rely on their keen senses to live and hunt under the dim light of stars. These <a href="https://doi.org/10.1086/702250">nighttime specialists avoid the competition of daylight hours</a>, hunting their prey under the cloak of darkness, often using a combination of night vision and acute hearing.</p>
<p>But was there nightlife 100 million years ago? In a world without owls or leopards, were dinosaurs working the night shift? If so, what senses did they use to find food and avoid predators in the darkness? To better understand the senses of the dinosaur ancestors of birds, <a href="https://scholar.google.com/citations?user=kHIW_0cAAAAJ&hl=en&oi=ao">our team</a> of <a href="https://scholar.google.com/citations?user=6qODxwoAAAAJ&hl=en&oi=ao">paleontologists</a> and <a href="https://scholar.google.com/citations?user=m_p_Lc0AAAAJ&hl=en&oi=ao">paleobiologists</a> scoured research papers and museum collections looking for fossils that preserved delicate eye and ear structures. And we found some. </p>
<p>Using scans of fossilized dinosaur skulls, in a paper <a href="https://science.sciencemag.org/content/372/6542/610?intcmp=trendmd-sci">published in the journal Science on May 6, 2021</a>, we describe the most convincing evidence to date for nocturnal dinosaurs. Two fossil species – <em>Haplocheirus sollers</em> and <em>Shuvuuia deserti</em> – likely had extremely good night vision. But our work also shows that <em>S. deserti</em> also had incredibly sensitive hearing similar to modern-day owls. This is the first time these two traits have been found in the same fossil, suggesting that this small, desert-dwelling dinosaur that lived in ancient Mongolia was probably a specialized night-hunter of insects and small mammals.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An artistic reconstruction showing _S. deserti as a small, feathered bipedal dinosaur with an owlish face." src="https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=848&fit=crop&dpr=1 600w, https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=848&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=848&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1066&fit=crop&dpr=1 754w, https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1066&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1066&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"><em>Shuvuuia deserti</em> had acute hearing and low-light vision that would have allowed it to hunt at night.</span>
<span class="attribution"><span class="source">Viktor Radermaker</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Looking to theropods</h2>
<p>By studying fossilized eye bones, one of us, Lars Schmitz, had previously found that some small predatory dinosaurs <a href="https://doi.org/10.1126/science.1200043">may have hunted at night</a>. Most of these potentially nocturnal hunters were theropods, the group of three-toed dinosaurs that includes <em>Tyrannosaurus rex</em> and modern birds. But to date, fossils for only <a href="https://doi.org/10.1126/science.1200043">12 theropod species included the eye structures</a> that can tell paleontologists about night vision.</p>
<p>Our team identified four more species of theropods with clues for their sense of vision – for a total of 16. We then looked for fossils that preserve the structures of the inner ear and found 17 species. Excitingly, for four species, we were able to get measurements for both eyes and ears.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A close up photo of the skull of _S. deserti_ showing a large eye socket." src="https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=378&fit=crop&dpr=1 600w, https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=378&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=378&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=475&fit=crop&dpr=1 754w, https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=475&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=475&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The eye socket – and specifically the sclerical ring – of <em>S. deserti</em> shows an eye with a very large pupil capable of letting in large amounts of light.</span>
<span class="attribution"><span class="source">Mick Ellison/American Museum of Natural History</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Eye bones built for night vision</h2>
<p>Scleral ossicles are thin, rectangular bone plates that form a <a href="https://doi.org/10.1002/ar.24043">ring-like structure surrounding the pupils</a> of lizards as well as birds and their ancestors – dinosaurs. Scleral rings define the largest possible size of an animal’s pupil and can tell you how well that animal <a href="https://doi.org/10.1016/j.visres.2010.03.009">can see at night</a>. The larger the pupil compared to the size of the eye, the better a dinosaur could see in the dark.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An owl skull with a cone like ring attached to the eye socket." src="https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=456&fit=crop&dpr=1 600w, https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=456&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=456&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=573&fit=crop&dpr=1 754w, https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=573&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=573&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This owl skull clearly shows the large scleral ring that helps animals see in darkness.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Bubo_virginianus_8zz.jpg#/media/File:Bubo_virginianus_8zz.jpg">David J. Stang/WikimediaCommons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Since the individual bony ossicles of these rings fell apart after these animals died more than 60 million years ago, our team made scans of the fossils and then digitally reconstructed the eyes. Of all the theropods we examined, <em>H. sollers</em> and <em>S. deserti</em> had some of the proportionally largest pupils.</p>
<p><em>S. deserti</em>‘s pupil made up more than half of its eye, very similar to night-vision specialists that live today like geckos and nightjars. Our team then compared the fossils to 55 living species of lizards and 367 species of birds with known day or night activity patterns. According to the statistical analyses our team performed, there is a very high chance – higher than 90% – that <em>H. sollers</em> and <em>S. deserti</em> were nocturnal.</p>
<p>But those were not the only two theropods our team looked at. Our analysis also found a few other likely nighttime specialists – such as <em>Megapnosaurus kayentakatae</em> – as well as daylight specialists like <em>Almas ukhaa</em>. But we also found some species – like <em>Velociraptor mongoliensis</em> – with eyesight seemingly adapted for medium light levels. This might suggest that they hunted around dawn or dusk.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two white plastic molds on a black background both with an elongated vertical base splitting into a 'y' shape at the top." src="https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Molds of the inner ear canal from a barn owl (left) and <em>S. deserti</em> (right) are almost identical, suggesting that the small dinosaur had incredible hearing.</span>
<span class="attribution"><span class="source">Shivan Parusnath/Wits University</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Incredible ears of a dinosaur</h2>
<p>In today’s nocturnal animals, <a href="https://doi.org/10.1002/bies.201600006">hearing can be as important as keen eyesight</a>. To figure out how well these extinct dinosaurs could hear, we scanned the skulls of 17 fossil theropods to decipher the structure of their inner ears and then compared our scans to the ears of modern animals.</p>
<p>All vertebrates have a tube-like canal called the cochlea deep in their inner ear. Studies of living mammals and birds show that the longer this canal, the <a href="https://doi.org/10.1098/rspb.2008.1390">wider the range of frequencies an animal can hear</a> and the better they can hear <a href="https://doi.org/10.1098/rspb.2008.1390">very faint sounds</a>.</p>
<p>Our scans showed that <em>S. deserti</em> had an extremely elongated inner ear canal for its size – also similar to that of the living barn owl and proportionally much longer than all of the other 88 living bird species we analyzed for comparison. Based on our measurements, among dinosaurs, we found that predators had generally better hearing than herbivores. Several predators – including <em>V. mongoliensis</em> – also had moderately elongated inner ears, but none rivaled <em>S. deserti</em>’s. </p>
<h2>The life of a nocturnal dinosaur</h2>
<p>By studying the sensory abilities of dinosaurs, paleontologists like us not only are learning what species roamed the night, but can also begin to infer how these dinosaurs lived and shared resources.</p>
<p><a href="https://doi.org/10.1126/science.abe7941"><em>S. deserti</em> had extreme night vision and sensitive hearing</a>, and this little dinosaur probably used its incredible senses to hunt prey at night. It could likely hear and follow rustling from a distance before visually detecting its prey and digging it up from the ground with its short single-clawed arms. In the dry, desert-like habitats of millions of years ago, it might have been an evolutionary advantage to be active in the cooler temperatures of the night. </p>
<p>But according to our analysis, <em>S. deserti</em> wasn’t the only dinosaur active at night. Other dinosaurs like <em>V. mongoliensis</em> and the plant-eating <em>Protoceratops mongoliensis</em> both lived in the same habitat and had some level of night vision.</p>
<p>Paleontologists currently do not know the full suite of animals that shared <em>S. deserti</em>’s extreme nocturnal lifestyle in the ancient deserts of Mongolia – it is rare to find fossils with the right bones intact that allow paleontologists to investigate their senses. However, the presence of a specialized night forager highlights that much like today, some dinosaurs avoided the dangers and competition of daylight hours and roamed under the stars.</p>
<p>[<em>Get the best of The Conversation, every weekend.</em> <a href="https://theconversation.com/us/newsletters/weekly-highlights-61?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=weeklybest">Sign up for our weekly newsletter</a>.]</p><img src="https://counter.theconversation.com/content/160152/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonah Choiniere receives funding from the National Research Foundation of South Africa. </span></em></p><p class="fine-print"><em><span>Roger Benson receives funding from the European Research Council, National Environments Research Council and Leverhulme Trust. </span></em></p><p class="fine-print"><em><span>Lars Schmitz does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>By looking at the eye bones and ear canals of extinct dinosaurs, researchers show that a small ancient predator likely hunted at night and had senses as good as a modern barn owl.Lars Schmitz, Associate Professor of Biology, Scripps CollegeJonah Choiniere, Professor of Dinosaur Paleontology, University of the WitwatersrandRoger Benson, Professor of Palaeobiology, University of OxfordLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1587372021-04-27T21:53:28Z2021-04-27T21:53:28ZHidden in plain sight: How the COVID-19 pandemic is damaging children’s vision<figure><img src="https://images.theconversation.com/files/395775/original/file-20210419-23-swymch.jpg?ixlib=rb-1.1.0&rect=17%2C0%2C1279%2C746&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Children’s increased screen time, exacerbated by remote learning during COVID-19, is directly contributing to increases in childhood myopia.</span> <span class="attribution"><span class="source">(iStock)</span></span></figcaption></figure><p>Eye doctors had planned to celebrate 2020 as the year of vision (as in seeing 20/20). Instead, it will be known as the year that worsened the world’s vision for decades to come. Scientists are attributing this latest health issue — one that is hidden in plain sight — to the pandemic.</p>
<p>Rates of myopia, also known as nearsightedness or shortsightedness, have been increasing worldwide for decades. Half of the world’s population is <a href="https://doi.org/10.1016/j.ophtha.2016.01.006">predicted to be myopic by 2050</a>.</p>
<p>The length of time children spend viewing digital screens has been exacerbated by a massive increase in remote schooling, directly contributing to further increases in childhood myopia. Home-schooled children of the COVID-19 era are at risk of becoming the visually compromised population of tomorrow.</p>
<p><a href="http://doi.org/10.1001/jamaophthalmol.2020.6239">A recent study</a> of more than 120,000 children in China demonstrated that six- to eight-year-olds who were in lockdown for the first six months of 2020 are more myopic than their counterparts from previous years. </p>
<h2>Myopia risks</h2>
<p>For a child with myopia, distance vision is blurry while near vision remains clear. In the past, the increase in myopia diagnoses from year to year was given little thought, since it was correctable with glasses or contact lenses. However, eye-care professionals now know that the younger a child becomes myopic, the higher their prescription may eventually become, and high prescriptions are bad news for eyes. </p>
<figure class="align-center ">
<img alt="Children sit behind desks in a classroom" src="https://images.theconversation.com/files/395815/original/file-20210419-23-1ubaqbf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/395815/original/file-20210419-23-1ubaqbf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/395815/original/file-20210419-23-1ubaqbf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/395815/original/file-20210419-23-1ubaqbf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/395815/original/file-20210419-23-1ubaqbf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/395815/original/file-20210419-23-1ubaqbf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/395815/original/file-20210419-23-1ubaqbf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Children’s increasing digital screen time is directly contributing to increases in childhood myopia.</span>
<span class="attribution"><span class="source">(iStock)</span></span>
</figcaption>
</figure>
<p>There is an established link between high myopia and <a href="http://doi.org/10.1016/j.preteyeres.2012.06.004">increased lifelong risk of devastating eye diseases</a>. Someone who has a prescription of more than six corrective units, or dioptres, (a prescription of -6.00) has a 90 per cent likelihood of being <a href="http://doi.org/10.1001/jamaophthalmol.2016.4009">visually impaired</a> by the age of 75.</p>
<p>A number of eye conditions are more prevalent in highly myopic adults including cataract, glaucoma, retinal detachment, retinal degeneration and other ocular diseases that can have a lifelong impact on their vision. These complications typically happen in later life, so concern for children may seem irrelevant or premature. However, there are other more immediate effects of high prescriptions. </p>
<p>A child or teenager with a fairly high prescription will be visually debilitated when not wearing their glasses or contacts, making them totally dependent on their vision correction. As an example, someone who has 10 dioptres of myopia sees anything beyond half an arm’s length as blurred. And don’t think that laser vision correction will save the day once they’re old enough. That degree of myopia may leave them <a href="https://www.webmd.com/eye-health/news/20191220/twenty-years-later-lasik-has-its-pros-and-cons">ineligible or subject to a less successful outcome</a>.</p>
<h2>Screen time</h2>
<p>The question then turns to what causes myopia in the first place, and what can be done about its onset and progression.</p>
<p>The biggest factor that can’t be changed is <a href="https://doi.org/10.1016/j.ajo.2020.05.026">parental myopia</a>. A child is extremely likely to become myopic if both parents are myopic. </p>
<p>One factor that is modifiable is the amount of time children spend on “near tasks,” those that involve viewing things closer than 40 centimetres from their eyes. </p>
<p>Extended periods of time spent focused on short distances is contributing to myopia increases. Digital screens have been targeted as the reason, but is it the electronic display itself or that a child holds a tablet or phone very close for extended periods? While there is some debate, <a href="https://dx.doi.org/10.1371%2Fjournal.pone.0134514">the short focusing distance</a> is the more likely culprit. </p>
<p>Even with the digital onslaught, all is not lost. Parents and caregivers can help prevent children from becoming nearsighted and slow down the rate at which the condition progresses.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/395819/original/file-20210419-17-j0ckyn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="infographic about myopia prevention" src="https://images.theconversation.com/files/395819/original/file-20210419-17-j0ckyn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/395819/original/file-20210419-17-j0ckyn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=423&fit=crop&dpr=1 600w, https://images.theconversation.com/files/395819/original/file-20210419-17-j0ckyn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=423&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/395819/original/file-20210419-17-j0ckyn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=423&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/395819/original/file-20210419-17-j0ckyn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=532&fit=crop&dpr=1 754w, https://images.theconversation.com/files/395819/original/file-20210419-17-j0ckyn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=532&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/395819/original/file-20210419-17-j0ckyn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=532&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Protecting children from myopia.</span>
</figcaption>
</figure>
<p>Simply <a href="https://dx.doi.org/10.1111%2Faos.13403">spending more time outside</a> can delay the onset of myopia. Direct sunlight plays a part, as well as the long-range focusing while playing outdoors. Restricting screen time is an option with optometrist-endorsed <a href="https://opto.ca/sites/default/files/resources/documents/childrens_vision_and_screen_time_en_march_2018_0.pdf">recommendations relating to screen times for children</a>. </p>
<p>For children schooled at home where limits are not practical, ensure that the screen is not being held or positioned too close to a child, encourage regular breaks and use the 20-20-20 rule: look 20 feet (seven metres) away every 20 minutes for 20 seconds. Some researchers have found that children who <a href="https://bhvi.org/news/sleeping-late-is-a-risk-factor-for-myopia-development-amongst-school-aged-children-in-china/">go to bed later</a> are more likely to be myopic — an added incentive for parents who are looking for reasons to call it a night.</p>
<p>A child’s myopia usually continues to progress until around the age of 16, but <a href="https://doi.org/10.1167/iovs.13-12403">about 10 per cent of myopic patients’</a> vision keeps worsening into their early 20s. </p>
<h2>Treatment and prevention</h2>
<p>Many options exist for vision correction, but more importantly, <a href="https://reviewofmm.com/current-treatments-in-myopia-management/">there are an increasing number</a> of options available to slow down the progression of myopia and <a href="https://doi.org/10.1097/opx.0000000000001367">reduce the risk</a> of developing sight-threatening complications in later life. They range from contact lenses and glasses specifically designed to slow down myopia progression to precisely formulated eye drops. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/395822/original/file-20210419-17-1l1totu.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="infographic about slowing myopia progression" src="https://images.theconversation.com/files/395822/original/file-20210419-17-1l1totu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/395822/original/file-20210419-17-1l1totu.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=750&fit=crop&dpr=1 600w, https://images.theconversation.com/files/395822/original/file-20210419-17-1l1totu.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=750&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/395822/original/file-20210419-17-1l1totu.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=750&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/395822/original/file-20210419-17-1l1totu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=943&fit=crop&dpr=1 754w, https://images.theconversation.com/files/395822/original/file-20210419-17-1l1totu.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=943&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/395822/original/file-20210419-17-1l1totu.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=943&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Ways to slow myopia progression in kids.</span>
<span class="attribution"><span class="source">(Alison Ng, CORE University of Waterloo)</span></span>
</figcaption>
</figure>
<p>These can be discussed with your eye-care practitioner, who will recommend the best path based on each child.</p>
<p>More than anything else, do not assume a child can see well. There is no substitution for an examination with an eye-care professional. The pandemic has already caused widespread hardship. By acting now, parents can minimize its impact on the vision and ocular health of generations to come.</p><img src="https://counter.theconversation.com/content/158737/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The COVID-19 pandemic has resulted in children spending more time on digital devices, which may have a long-term impact on their vision, including the risk of myopia.Debbie Jones, Clinical Professor, School of Optometry & Vision Science and Clinical Scientist, Centre for Ocular Research & Education (CORE), University of WaterlooKate Gifford, Visiting Research Fellow in Optometry and Vision Science, Queensland University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1435772021-04-26T17:54:07Z2021-04-26T17:54:07ZHigh-tech contact lenses are straight out of science fiction — and may replace smartphones<figure><img src="https://images.theconversation.com/files/396361/original/file-20210421-15-vvrmzt.jpg?ixlib=rb-1.1.0&rect=6%2C12%2C4083%2C2139&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A concept image showing a contact lens with digital and biometric implants.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>Contact lenses are the result of an accidental discovery made during the Second World War. Ophthalmologist Harold Ridley noticed that despite acrylic plastic shrapnel shards becoming embedded in the eyes of fighter pilots, it did not appear to cause any harm. This finding eventually led <a href="https://doi.org/10.1016/s0039-6257(96)82003-0">to the creation of hard intraocular lenses for the treatment of cataracts</a>. </p>
<p>Over the years, new scientific discoveries have led to softer and more comfortable contact lenses. And now, research bringing together chemistry, biology and microelectronics is resulting in contact lenses that are straight out of science fiction.</p>
<h2>Current research</h2>
<p>Researchers at the Hong Kong University of Science and Technology have developed a prototype of a contact lens that <a href="http://dx.doi.org/10.1016/j.sna.2013.08.029">continuously monitors changes in intraocular pressure, the pressure within the eyeball</a>. The prototype is based on the fact that the shape of the eyeball varies in response to changes in intraocular pressure. As this happens, the contact lens undergoes commensurate change in shape. A thin capacitor embedded within the contact lens correlates changes in shape to variations in intraocular pressure. </p>
<p>The continuous monitoring provided by the contact lens could come in handy for people suffering from glaucoma. This lens can monitor changes in intraocular pressure throughout the day, and can responsively release drugs to alleviate the glaucoma. A similar lens, called <a href="https://dx.doi.org/10.2147/OPTH.S109708">Sensimed Triggerfish</a>, has received regulatory approval in the <a href="https://www.accessdata.fda.gov/cdrh_docs/reviews/DEN140017.pdf">United States</a> and <a href="https://eyewire.news/articles/sensimed-announces-approval-of-the-sensimed-triggerfish-in-japan/">Japan</a>.</p>
<p>Thanks to the ubiquity of electronic devices, we are currently living in a world constantly bathed in electromagnetic radiation. Although a clear consensus is absent, studies have pointed out that exposure to electromagnetic radiation could <a href="https://dx.doi.org/10.4062/biomolther.2018.152">possibly induce some effects in human tissue</a>. Engineers in South Korea have applied a layer of graphene to contact lens to help shield the eyes from electromagnetic radiation. The thin graphene layer <a href="https://doi.org/10.1021/acsnano.7b00370">also reduces dehydration</a>.</p>
<h2>Beyond vision</h2>
<p>Developments in microelectronics and chemistry have contributed to the surge in projects and prototypes involving smart contact lenses. For example, there are already lenses that function as in-eye sunglasses, darkening and lightening in response to changes in light intensity.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/eeP1H-XFieI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">An Atlanta-based optometrist reviews Johnson & Johnson’s transitional lenses.</span></figcaption>
</figure>
<p>California-based tech start-up Mojo Vision is working on contact lenses with an inbuilt LCD display, which opens up enormous possibilities. Similar to a <a href="https://www.digitaltrends.com/cars/best-head-up-displays/">head-up display projected on a car’s windshield</a>, the contact lens can provide a wide range of information, from phone notifications, map directions and more. </p>
<p>It’s not too far-fetched to imagine that we will soon be able to use contact lenses to zoom in on distant objects.</p>
<h2>Replaced devices?</h2>
<p>As a chemical engineering doctoral student, I have been involved with projects focused on developing very thin <a href="https://doi.org/10.1002/ppap.202000191">nano-sized polymer films on contact lenses</a>. These films enhance comfort and attach tiny sensors to the surface to prevent unwanted substances from sticking. </p>
<p>Challenges remain in scaling up the mass production of such products and keeping the price accessible. Critics have also pointed out that <a href="https://doi.org/10.1016/j.ophtha.2016.04.003">it is easier to correct vision deficiencies with advancements in laser technology</a>. </p>
<p>The global contact lens market is predicted to expand, and we can expect to see a plethora of ground-breaking products being released. And as technology continues to develop contact lenses, smart contact lenses may one day replace smartphones and screens.</p><img src="https://counter.theconversation.com/content/143577/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bishakh Rout does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Contact lens technology is reaching the point where science fiction meets reality. From interfaces to pressure monitors and drug release features, the contact lens industry is about to be disrupted.Bishakh Rout, PhD student, Chemical Engineering, McGill UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1579162021-04-18T12:51:50Z2021-04-18T12:51:50ZCurious Kids: What do blind people experience in their dreams?<figure><img src="https://images.theconversation.com/files/394320/original/file-20210409-21-1mj6tit.jpg?ixlib=rb-1.1.0&rect=36%2C18%2C5970%2C3989&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The dreams of a person without sight since birth can be just as vivid and imaginative as those of someone with normal vision.</span> <span class="attribution"><span class="source">(Unsplash)</span></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption"></span>
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<p><em>Curious Kids is a series for children of all ages. Have a question you’d like an expert to answer? Send it to <a href="mailto:curiouskidscanada@theconversation.com">CuriousKidsCanada@theconversation.com</a>.</em></p>
<blockquote>
<p>What do blind people experience in their dreams? — James</p>
</blockquote>
<p>Humans are extremely visual. Nearly <a href="https://www.rochester.edu/pr/Review/V74N4/0402_brainscience.html">half of our brain is devoted to processing visual information</a>. Most of the brain networks responsible for providing vision <a href="https://faculty.washington.edu/chudler/plast.html">are established early in life</a>.</p>
<p>This means that <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3722610/">from about the time of birth we begin our lifelong collection of experiences and memories</a> that strongly rely on vision. </p>
<p>Throughout life, we associate most of our interactions with visual images rather than with experiences from our other senses such as hearing or smell. </p>
<p>For those of us with normal vision, <a href="https://doi.org/10.1016/j.tics.2009.12.001">dreams are full of the visual images we experience during our waking life</a>. To understand what blind people experience in their dreams, we must distinguish the experiences of those who were blind at birth from those that became blind later in life. </p>
<h2>Just as vivid and imaginative</h2>
<p>Humans born without sight are not able to collect visual experiences, so <a href="https://www.scientificamerican.com/article/superpowers-for-the-blind-and-deaf/">they understand the world entirely through their other senses</a>. As a result, people with blindness at birth develop an amazing ability to understand the world through the collection of experiences and memories that come from these non-visual senses. </p>
<figure class="align-center ">
<img alt="Woman waking up in bed" src="https://images.theconversation.com/files/394333/original/file-20210409-21-1n9k6kp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/394333/original/file-20210409-21-1n9k6kp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=429&fit=crop&dpr=1 600w, https://images.theconversation.com/files/394333/original/file-20210409-21-1n9k6kp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=429&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/394333/original/file-20210409-21-1n9k6kp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=429&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/394333/original/file-20210409-21-1n9k6kp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=539&fit=crop&dpr=1 754w, https://images.theconversation.com/files/394333/original/file-20210409-21-1n9k6kp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=539&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/394333/original/file-20210409-21-1n9k6kp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=539&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The dreams of people who develop blindness later in life become less visual as their time without vision increases.</span>
<span class="attribution"><span class="source">(Kinga Cichewicz/Unsplash)</span></span>
</figcaption>
</figure>
<p>The dreams of a person who has been without sight since birth can be just as vivid and imaginative as those of someone with normal vision. They are unique, however, because their <a href="https://wtamu.edu/%7Ecbaird/sq/2020/02/11/do-blind-people-dream-in-visual-images/">dreams are constructed from the non-visual experiences and memories they have collected</a>. </p>
<p>While a person with normal vision will dream about a familiar friend using visual memories of shape, lighting and colour, a blind person will associate the same friend with a unique combination of experiences from their non-visual senses that act to represent that friend. </p>
<p>In other words, people blind at birth have similar overall dreaming experiences but <a href="https://www.bbc.com/news/blogs-ouch-28853788">they do not dream in pictures</a>. </p>
<p>The dream experience of a person who lost vision later in life is very different than someone who never had vision. People that lose vision later in life had the ability to collect many visual experiences that can appear in their dreams and in a manner very similar to a sighted person. </p>
<p>Interestingly — and perhaps expected — <a href="https://doi.org/10.1016/j.sleep.2013.12.008">the dreams of people who develop blindness later in life become less visual as their time without vision increases</a> and as they collect more experiences without vision. </p>
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<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidscanada@theconversation.com">CuriousKidsCanada@theconversation.com</a>. Please tell us your name, age and the city where you live.</em>
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<p class="fine-print"><em><span>Kevin Duffy receives funding from the Natural Sciences and Engineering Research Council of Canada, and from the Canadian Institutes of Health Research. </span></em></p>A curious kid asks: what do blind people experience in their dreams?Kevin Duffy, Professor, Department of Psychology and Neuroscience, Dalhousie UniversityLicensed as Creative Commons – attribution, no derivatives.