What causes nearsightedness? It doesn't appear to be genetic. Spending lots of time outdoors while growing up seems to greatly reduce the chances of being nearsighted. - Amit Patel

"Near work, such as reading, had always seemed like an obvious contributor, since short-sightedness appears more common among highly educated people." - Clare Dibble

"Playing indoor sports turned out to have no benefits for the eyes, whereas even physically inactive time spent outside was beneficial" - Clare Dibble

"The result? On average the children in Sydney spent nearly 14 hours per week outside, and only 3 per cent developed myopia. In contrast, the children in Singapore spent just 3 hours outside, and 30 per cent developed myopia. Once again, close work had a minimal influence; the Australian children actually spent more time reading and in front of their computers than the Singaporeans (Archives of Ophthalmolology, vol 126, p 527). But why should the great outdoors stave off myopia? One possibility is that the sheer intensity of light outdoors somehow stalls eyeball growth, a theory supported by Regan Ashby's work at the University of Tübingen in Germany. Ashby attempted to induce myopia in a group of chicks by blurring their vision using special lenses. He divided the birds into three groups and exposed them to different light levels for just 15 minutes each day. At the end of the five-day trial, those exposed to intense light - half as bright as direct sunlight and 30 times brighter than normal indoor lighting - were on average 40 per cent less short-sighted than chicks exposed to normal laboratory light levels during those 15 minutes. Actual daylight slashed the severity of myopia by a further 40 per cent (Investigative Ophthalmology and Visual Science, DOI: 10.1167/iovs.09-3419). Although the mechanism behind this remains uncertain, Ashby believes bright light may stimulate the retina to produce high levels of dopamine, a substance known to inhibit eye growth." - bob

My optometrist was very impressed that my myopia is getting better. He thinks it's because I take off my glasses to read, but now I think it's because I spent a lot more time outside than others. - Piaw Na

My myopia stopped getting worse when I started going out more, but there were so many other lifestyle changes at the time that it's hard for me to say whether it had an effect. For example, when outdoors I also exercise more :) (hiking, mostly) - Amit Patel

Our 9 month old son loves being outside. Maybe this will mean that he won't be as near-sighted as I am. - Robert Felty

FWIW, I've heard that sleeping with a night light can cause myopia... - Andrew C

This peripheral blur theory sounds very interesting. I actually only need my glasses to drive or watch TV/movies... I should get back to what I used to do for years, which was go without the rest of the time. I've needed lenses for nearly 20 years now, but the progression (degradation) has been very very slow. - Andrew C