Evidence That Myopia Has a Strong Environmental Cause

Time reports on a new study on why Asians have a higher rate of nearsightedness:

It has long been thought that nearsightedness is mostly a hereditary problem, but researchers led by Ian Morgan of Australian National University say the data suggest that environment has a lot more to do with it.

Reporting in the journal Lancet, the authors note that up to 90% of young adults in major East Asian countries, including China, Taiwan, Japan, Singapore and South Korea, are nearsighted. The overall rate of myopia in the U.K., by contrast, is about 20% to 30%.

“We postulate that bright outdoor light would stimulate the release of the retinal transmitter dopamine, which is known to be able to block the axial growth of the eye, which is the structural basis of myopia — the eye simply grows too big.” Morgan notes that both Chinese and Caucasian children living in Australia have lower rates of nearsightedness. 

 

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  1. RGJ says:

    The paragraph summarizing is a bit confusing…basically the study says that if you stay indoors in poor light studying, as Asian children do in their home countries, you get nearsighted. If you are out in the sun as a kid, you don’t.

    So, turn a light out when you are trying to read, or you’ll go blind. My mom knew that.

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  2. Eric M. Jones says:

    And the myriad other studies that find the opposite are what…just wrong?

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  3. Enter your name... says:

    I’ve long wondered what the US rates were, and whether it varied by lifestyle choices. It seemed to me that practically every student at my (moderately elite) college needed glasses.

    Does the “bright light” need to hit the eyeball, or just the skin? The usual method of getting exposure to bright lights is to go outside, and sunlight causes cataracts. Do cataract-preventing sunglasses cause nearsightedness?

    If I’m nearsighted now, can I reverse it by spending more time in brightly lit places, or is it too late?

    (So Grandma *was* right: spending a lot of time in the dark does ruin your eyes!)

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  4. Sophie says:

    Does being in medical school counts as an adverse environment? What’s the difference between medical schools in the north (less light) and the ones in the south?

    - alittlehappi.blogspot.com

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  5. m.m. says:

    Just a bad summary on Freakonomics’ part. Here’s a better encapsulation of the issue from the article:
    —-
    The scientists think that the neurotransmitter dopamine may play a significant role in the structural development of the eyeball. Exposure to light increases the levels of dopamine in the eye, which may prevent elongation of the eyeball.

    “We think there is a pretty well-confirmed mechanism,” says Morgan. “We postulate that bright outdoor light would stimulate the release of the retinal transmitter dopamine, which is known to be able to block the axial growth of the eye, which is the structural basis of myopia — the eye simply grows too big.” Animal experiments using mice and monkeys support the theory, the researchers say.
    —-
    Basically, if you don’t get enough bright light, then your eye grows too long, and the focal length of your lens will be in front of the retina instead of on it.

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  6. James says:

    Perhaps it has less to do with the amount of light, than with a “use it or lose it” effect. If you spend all your time indoors during your formative years, seldom requiring the eye to focus on anything closer than a book or video screen, is it at all surprising that the eyes adapt to these conditions?

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  7. frankenduf says:

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  8. Joe Dokes says:

    It was my understanding that continued focus at a set focal length relatively near the face caused nearsightedness, think long hours of reading.

    That always made sense. Spend many hours glued to a book, you’ll end up nearsighted. The confirmation for this was supposedly Native Peoples of Alaska, who allegedly didn’t need glass until they were taught to read.

    Made sense to me, of course it could simply mean that no one was giving eye tests until after schooling became common, so the correlation simply didn’t exist.

    Regards,

    Joe Dokes

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    • Enter your name... says:

      The same data set could support their theory:

      Where does reading instruction take place? Indoors, where the light is lower than outdoors.

      What is one major difference between a literate and illiterate child from a century ago? The amount of time spend indoors during the day, where the light is lower.

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