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Monday’s medical myth: reading in dim light ruins your eyesight

The idea that reading in dim light ruins your eyes isn’t my favourite wives' tale about “leisure activities” causing blindness, nor is it the most obscene! In any case, it’s simply not true. I’ll begin…

You won’t ruin your eyes but you may get a headache. Martin Gommel

The idea that reading in dim light ruins your eyes isn’t my favourite wives' tale about “leisure activities” causing blindness, nor is it the most obscene! In any case, it’s simply not true.

I’ll begin my expose´ with a brief explanation of how we see.

The eyes are equipped to catch the light reflected off, or generated by, objects in our world. When light enters our eyes, it’s focussed by the front layers of the eye onto the retina – a delicate layer of just a few rows of cells, less than half a millimeter thick – which sits at the back of the eye.

Amanda Venner

The light that falls on the retina is referred to as the image. The retina begins the process of decoding the image and sorting this into information that tells our brains about its brightness, colour, shape, size, and movement. The information, in the form of neural signals, is then passed back to the brain, which further processes the data before bringing it to the attention of our conscious mind.

Some animals, such as owls, have retinas that are specialised for seeing even the tiniest amount of light. Put simply, they see clearly in conditions that we consider pitch black because their retinas contain “rod” detectors. These rods are very sensitive, but can’t decode colour (owls are colour blind). There are close to 60,000 of these rods per square millimetre of retina, which translates to owls' incredible sensitivity and sharpness of vision – called acuity.

Humans also have many rods, which is why we’re able to see when driving at night when there’s very little light around. But rods become useless in bright or even normal light levels. That’s why we also have “cones”, which are much better in daylight and allow us to see colour. These cones can be found throughout the retina, with the greatest number in the centre.

When you turn off the lights, your “night vision” gradually kicks in over six or seven minutes, as you stop using your cones and start using your rods.

The rods in your eyes help you see at night but they’re not so useful for reading. Flickr/Ianier

There are no rods at the centre of the human retina which gives rise to the fact that we have low sensitivity to dim light in our central vision. That’s why, when you go outside on a clear night and look directly up at a faraway star, you won’t be able to see it. You can only see a star by looking to the side of it, thus using your rods.

On the flipside, in order to read, we practically only use the cones in the centre of our vision. To test this for yourself, try reading a column on the screen while looking just to the side of that column – impossible.

So reading in dim light – or reading at all – is possible when there is enough light around for the cones to pick up a signal.

Your eyes won’t be harmed but you may give yourself a headache. This is because, from an evolutionary perspective, the eyes weren’t designed for straining to see close-up objects for sustained periods. They are much better suited for looking out into the distance over fields of buffalos (not that many of us have that luxury in our modern-day lives).

Of course, eyestrain – the feeling of tired or aching eyes and headache – may indicate that you need glasses, or perhaps the glasses you’re wearing may need an update. If you are concerned about the health of your eyes, see your optometrist for a check up.

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31 Comments sorted by

  1. Russell Hamilton

    Librarian

    Thanks Harrison - I like the rods and cones thing.

    Please go further: is flourescent light bad for your eyes? Having moved to compact flourescent globes, should I, for the sake of my aching eyes, move to LEDs?

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  2. A Lamb

    logged in via email @gmail.com

    And what about reading a book in the sun. Does the brightness of the page damage the eyes?

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  3. Doug Cotton

    IT Manager

    While on the subject of healthy eyes, perhaps the best supplementation is zeaxanthin and lutein. Carotenoids are very numerous; more than 600 are found in red, yellow, green, and orange vegetables and fruits. Carotenoids like zeaxanthin and lutein have highly antioxidative characteristics and help prevent destructive vascular changes in the macula, decreasing the risk of age-related macular degeneration. Studies indicate that high levels of lutein may decrease the incidence of posterior subcapsular cataracts, diminish complaints of glare, and provide better color vision and more critical acuity (Bone RA et al 2001).

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    1. Doug Cotton

      IT Manager

      In reply to Tim Scanlon

      1. Schalch W. Possible contribution of lutein and zeaxanthin, carotenoids of the macula lutea, to reducing the risk for age-related macular degeneration: a review. HKJ Ophthalmol. 4(1).

      2. Semba RD, Dagnelie G. Are lutein and zeaxanthin conditionally essential nutrients for eye health? Med Hypotheses. 2003 Oct;61(4):165-72.

      3. Krinsky NI, Landrum JT, Bone RA. Biologic mechanisms of the protective role of lutein and zeaxanthin in the eye. Annu Rev Nutr. 2003:23:171-201.

      4. Krinsky NI. Possible biologic mechanisms for a protective role of xanthophylls. J Nutr. 2002 Mar;132(3):540S–542S.

      5. Snodderly DM. Evidence for protection against age-related macular degeneration by carotenoids and antioxidant vitamins. Am J Clin Nutr. 1995 Dec;62(6suppl): 1448S–1461S.

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    2. Doug Cotton

      IT Manager

      In reply to Tim Scanlon

      There are other papers and, as it happens, this was a topic I studied in some detail whilst doing post-graduate studies in Natural Medicine through Swinburne University, Melbourne around 2004-5. I am not going to stop taking it I can assure you, and at nearly 66 I can still read the bottom line on eye charts and 5 point type, never wearing glasses. Anecdotal Iknow.

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    3. Mark Harrigan

      PhD Physicist

      In reply to Doug Cotton

      Good Grief! Doug Cotton is everywhere offering his pseudo science advice. Climate Science, Diet and now eye health. My goodness the man is a veritable Polymath!

      Only trouble appears to be that, according to the trained people in every field in which he purports to have expertise, he is a polymath who cannot add up and whose claims are totally unsupported by any evidence

      But no matter. He has Faith.

      I think they used to call such people Witch Doctors?

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    4. Doug Cotton

      IT Manager

      In reply to Mark Harrigan

      What's your problem? I have done post graduate studies in Natural Medicine through Swinburne University, including an assignment on "eye health" as you call it. I have also studied research in natural medicine privately for 36 years. And I have completed (with High Distinction) a Diploma in Nutrition. If you care to read all the medical threads on which I have posted you will find some positive response. I am of course aware that it is an area where research is accepted rather slowly.

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    5. Mark Harrigan

      PhD Physicist

      In reply to Doug Cotton

      I think Tim's reply makes it clear what the "problem" is with your pseudo science

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    6. Doug Cotton

      IT Manager

      In reply to Rosemary Stanton

      The following excerpts from http://www.mdsupport.org/library/lutzean.html are relevant ...

      "According to a 1995 study, increasing the consumption of dark green, leafy vegetables appears to offer some protection against macular degeneration. Because nutritional factors may play a role in AMD, researchers decided to correlate the disease with dietary antioxidant intake in subjects participating in the NIH Eye Disease Case-Control Study (Seddon JM et al. JAMA. 1994; 272: 1413-1420).

      The investigators…

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    7. Doug Cotton

      IT Manager

      In reply to Rosemary Stanton

      Glutathione, which is particularly concentrated in the lens, has been shown to have a hydroxyl radical-scavenging function in lens epithelial cells. (1)

      Lutein and zeaxanthin, the primary carotenoids concentrated in the macula, counter the free-radical forming action of light and oxygen. It's been suggested that macular pigment protects the retina via a dual role that includes scavenging for free radicals and filtering out blue light, which can cause photochemical damage. Some studies have also…

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    8. Doug Cotton

      IT Manager

      In reply to Mark Harrigan

      Dr Mark Harrigan has a PhD in Atomic Physics - not anything to do with natural medicine which I have studied, not only in a post graduate course through Swinburne University, but also privately for 36 years at least. I also gained (with High Distinction) a Diploma in Nutrition.

      Dr Harrigan is a self-professed "Climate Consultant" running his own business advising local councils etc how to reduce their emissions - not much to do with the topic of this thread. He has been upset because of my application…

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    9. Mark Harrigan

      PhD Physicist

      In reply to Doug Cotton

      Doug Cotton really does make it up as he goes along. I am no "Climate Consultant" (self professed or otherwise) and have never advised any local councils on anything, ever (where did you make that one up from Mr Cotton?).

      I make no claim at all in relation to competency in the field for this article. I just read the article because I like the conversation. (I would like it a whole lot better if people like Mr Cotton didn;t use it as platform to self promote)

      And here I find that Doug Cotton is…

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    10. Doug Cotton

      IT Manager

      In reply to Tim Scanlon

      Yes it would be "hit and miss" with the low doses they used in that study and the selection of patients "age: 71.5 [±7.1] years), of which 92.6% exhibited features of age-related macular degeneration (AMD), received a daily supplement consisting of 12 mg L and 1 mg Z"

      The supplement I take has 38mg L and 3.75mg Z - need I say more?

      I am not claiming a cure - merely an increased probability of not getting MD.

      At my last eye check he was amazed at the quality of my retina at age 65 - quite apart from my not needing glasses to read 5 point type, distant signs and the last row of an eye chart.

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    11. Doug Cotton

      IT Manager

      In reply to Rosemary Stanton

      The paper Tim quoted involved people who were old and already had MD.

      The doses they used were just over one quarter of a typical recommended dose such as contained in a single small capsule I take daily.

      Numerous studies do just this - set out to prove nutrients don't cure, whereas the real benefit lies in protecting healthy people by reducing the probability of their contracting the disease. And may such studies use ineffective doses.

      Please read my subsequent posts herein.

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    12. Doug Cotton

      IT Manager

      In reply to Tim Scanlon

      If there is one area of the body in which primates are pretty similar to humans it would be the eyes.

      Read my subsequent posts on all this.

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    13. Doug Cotton

      IT Manager

      In reply to Mark Harrigan

      My genuine apologies regarding the "climate consultant" reference. That was Ben Heard who you will remember wrote similar posts. His website is http://www.thinkclimateconsulting.com.au/ Your business is in software distribution I understand.

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    14. Mark Harrigan

      PhD Physicist

      In reply to Doug Cotton

      Still wrong, and in any event irrelevant to this thread. I wonder if your eyes are really as good as you claim?

      But aplogy accepted. Thanks

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    15. Rosemary Stanton

      Nutritionist & Visiting Fellow at University of New South Wales

      In reply to Doug Cotton

      Doug, there is plenty of evidence that lutein and zeaxanthin are involved in the macula and in eye health. That is not in dispute. And as you have noted, there are studies showing value for some aspects of eye health associated with consumption of dark green leafy vegetables. But that doesn't translate into claiming that supplements of two carotenoids will have the same effect as eating vegetables. The vegetables, after all, contain an amazing;y complex array of substances, including several hundred…

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    16. Lisa Simpson

      Procrastinator

      In reply to Doug Cotton

      Doug, I teach a science subject to natural medicine students. I can tell you with certainty that some of what they learn as fact in their clinical subjects is sometimes pseudoscience rubbish.

      If some of the claims made in their journals (peer reviewed by eg. naturopaths for other naturopaths) were for real they'd probably be on the front cover of Nature/Lancet/JAMA etc

      (Oh, yeah I forgot, all major journals are part of self-serving conspiracies by scientists to get rich through research grant funding....)

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    17. Lisa Simpson

      Procrastinator

      In reply to Mark Harrigan

      hey, at least he's consistant in never believing anything offered up by mainstream science!

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    18. Doug Cotton

      IT Manager

      In reply to Rosemary Stanton

      Rosemary - it is also worth noting that supplementation of other antioxidants achieved a significant 25% reduction in the risk of developing advanced AMD (see above link)

      "The first NEI-sponsored AREDS, a 10-year study completed in 2006, found that a daily supplement containing high levels of several antioxidants and zinc reduced the risk of developing advanced AMD by about 25 percent.

      "The multivitamin supplement used in the first AREDS contained:

      Vitamin C - 500 mg
      Vitamin E - 400 IU
      Beta-carotene - 15 mg (equivalent of 25,000 IU of vitamin A)
      Zinc (as zinc oxide) - 80 mg
      Copper (as cupric oxide) - 2 mg"

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    19. Doug Cotton

      IT Manager

      In reply to Mark Harrigan

      Dr Harrigan: The US Government's "National Eye Institute" conducted a 10 year study which using supplements of various antioxidants, including 400mg vitamin E, and found a significant 25% reduction in the risk of developing advanced macular degeneration. This is just one of hundreds of peer-reviewed papers establishing significant benefits due to supplementation of various nutrients.

      Read carefully this page and remember the National Eye Institute is one of the US Government's national health institutes .. http://www.nei.nih.gov/news/statements/vitamine.asp

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  4. John Harland

    bicycle technician

    To what degree does the ratio of rod:cones differ between individuals?

    Is there a gender difference?

    Some people can read in dimmer light than others. Is everybody's fovea entirely devoid of cone cells?

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  5. Doug Cotton

    IT Manager

    Here is a relevant excerpt from the US Government's National Eye Institute's website.* It is based on their government-sponsored 10 year study on the use of vitamin E and C, zinc etc for those at risk of developing Age-related Macular Degeneration.

    "Can diet alone provide the same high levels of antioxidants and zinc as the AREDS formulation?

    No. The high levels of vitamins and minerals are difficult to achieve from diet alone. However, previous studies have suggested that people who have diets rich in green leafy vegetables have a lower risk of developing AMD.

    Can a daily multivitamin alone provide the same high levels of antioxidants and zinc as the AREDS formulation?

    No. The formulation's levels of antioxidants and zinc are considerably higher than the amounts in any daily multivitamin."

    * http://www.nei.nih.gov/health/maculardegen/armd_facts.asp

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  6. Archie McGeorge

    Ophthalmologist

    Hi Harrison -nice article on a persistent myth. I've come very late to the conversation after following a link to a more recent post.

    I'd like to suggest that you expand the post to cover some of the other reasons that people struggle to read in low light -although it certainly does them no harm.

    The primary one is undoubtedly the optical effect of a larger pupil as light drops. This reduces the depth of focus of the eyes optics -analogous to the shallow depth of field used by portrait photographers…

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  7. Allen Tsai

    Medical Specialist

    I am convinced that reading in dim light is not harmful in most situation , however, it is supposed to be based upon several facts

    First of all , I suppose you are not a potential victim of angle-closure glaucoma which often happens in middle age with hyperopia . Secondly , if you are a child who is still during the development of vision and your eyeball is still growing , reading in the dim light would be apt to trigger your eyeball elongation which indicates high myopia in the future . Finally…

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