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Exposure to very bright light (even standing under a shade tree on a cloudy day is far brighter than normal indoor lighting) specifically during key years had b
by corrral 4y ago
Exposure to very bright light (even standing under a shade tree on a cloudy day is far brighter than normal indoor lighting) specifically during key years had been nailed down with high confidence as the primary cause of most near-sightedness, last time I looked into this.
Not sure if they'd figured out the mechanism, but speculation was that bright light is involved in signaling the eye to stop lengthening at the right time.
IOW the cause is, basically, school. In Winter months, kids may hardly see the Sun at all, with very short days and recess often indoors (too cold, too snowy, too wet) especially as schools have seemed to grow more wary of taking kids out in poor weather, over the last few decades. Plus anything else that keeps kids indoors, sure (video games, social media[0]) but school seems to be a lot of it.
[0] And actually, the social media factor likely kicks in well after it matters. Ditto video games unless your kid becomes a gaming addict in the 3-7 age range and you just let that happen.
- exceptione 4y agoIf exposure to bright light is the primary cause of most near-sightedness, than not seeing the sun would be beneficial. I don´t get it, typo?
- dan-robertson 4y agoYeah typo. The theory is that eyes change shape over time (I think starting out longsighted) and at some point a hormone is released to stop this changing. It is released when (a) the eyes are typically around the middle of their focal range (ie looking at middle-distance things is done with relaxed eyes) and (b) there is a lot of light. Without the second condition the shape of the eyes will continue to change and then you get myopia.
- derefr 4y agoSee also: metabolic bone disease in lizards. Also caused by a lack of light — in their case, near-UV light. (My understanding is that the thing changing the shape of the eye over time is the development of the orbital socket bones — so nearsightedness and MBD could have more in common than it seems.)
- corrral 4y agoYeah, typo, too late to edit. Insufficient exposure to bright light during key, early years while the eye is developing was found to increase risk so much that it's practically all that matters, at least over a population (I'm sure some unlucky people get it for other reasons, like most things)
- wenc 4y agoI grew up near the equator where there is a very high rate of myopia despite exposure to sunlight. (Sure we spent a lot of time indoors, but we were exposed to sunlight all year round since there’s only one season: summer). I think genetics has a larger predictive effect than sunlight.
- doliveira 4y agoThere's a reason why they're not just saying "it's genetics"...
- deleted 4y ago[deleted]
- barry-cotter 4y ago> I think genetics has a larger predictive effect than sunlight. We know this isn’t true because Singapore is practically on the equator and went from less than 10% myopia to over 90% in ~50 years.
- wenc 4y agoRight with the same amount of sunlight. I’ll grant that with indoor malls and public transit there’s less exposure to direct sunlight, but you still can’t avoid being exposed to the sun daily in Singapore.
- lmm 4y agoThe amount of time you spend in sunlight matters. Kids went from running around outdoors all day (whether for work or play) to spending all day sitting in classrooms.
- djtango 4y agoAre you familiar with Singaporean norms? There is/was a very strong aversion to being outdoors, especially during peak sunlight hours (lunchtime). This compounds with both study culture and digital culture (videogames + tv + phones) and less of a celebration of sports to mean many kids get less direct sunlight than you'd think. Especially now everyone is terrified of UV
- irrational 4y agoHave any studies been done comparing children raised in Portland and Seattle (where it rains for the majority of the year so kids spend a lot of time indoors) versus San Diego or some other sunny city?