Actually, we've a pretty good idea why, from looking at countries with very, very high levels of short sightedness. The article itself actually references these (mainly conducted in South Korea and the US).
It appears that it's down to people not getting enough sunlight as children. The sun is, obviously, very bright, which forces your iris to have to contract and relax a lot, which keeps both those muscles and the lens in good health.
With populations increasing having children that stay inside, they're not exposed enough to that much harsh, bright light, so their irises weaken, leading to short sightedness.
Caveat - a lot of the research of this is looking at factors that correlate with the levels of vision reported, so the cause is being inferred, rather than know. However, it's a decent hypothesis, and the more recent meta-analysis studies done seem to be supporting this.
The problem is that once it's happened, it doesn't appear to be something that can be "cured" by re-introducing bright light exposure.
I read somewhere (it was a while ago so can't remember) that it was to do with people spending a lot of time indoors, and never needing to look off into long distances.
Personally I do a fair bit of outdoor sports, and I have one eye thats fine and one that is quite badly short sighted.
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[ 2.5 ms ] story [ 11.0 ms ] threadIt appears that it's down to people not getting enough sunlight as children. The sun is, obviously, very bright, which forces your iris to have to contract and relax a lot, which keeps both those muscles and the lens in good health.
With populations increasing having children that stay inside, they're not exposed enough to that much harsh, bright light, so their irises weaken, leading to short sightedness.
Caveat - a lot of the research of this is looking at factors that correlate with the levels of vision reported, so the cause is being inferred, rather than know. However, it's a decent hypothesis, and the more recent meta-analysis studies done seem to be supporting this.
The problem is that once it's happened, it doesn't appear to be something that can be "cured" by re-introducing bright light exposure.
Personally I do a fair bit of outdoor sports, and I have one eye thats fine and one that is quite badly short sighted.