I started wearing glasses at 12. I had always picked seats close to the chalkboard but the reason why didn't make sense until, even up close, text became blurry. I am identical in prescription and astigmatism to my father so this would indicate my near-sightedness has its basis in inherited genes.
However, these stats for environmentally generated myopia are incredible! "Sixty years ago, 10–20% of the Chinese population was short-sighted. Today, up to 90% of teenagers and young adults are. In Seoul, a whopping 96.5% of 19-year-old men are short-sighted."
Also cool, your retina produces dopamine! It turns out that dopamine release has a significant effect on your circadian rhythm, which makes sense. Your eye is clearly attuned to daylight. A special kind of cell in your eye (dopaminergic cell) reacts to light and releases dopamine. Dopamine is produced and released at higher rates during the day than at night. The special dopaminergic cell's neurons control the production of serotonin and melatonin. Melatonin is a hormone that helps us sleep and is normally produced when it's dark outside (or in some cases, when daylight is decreasing). Melatonin causes a decrease in dopamine release and dopamine can stop melatonin production, it's a delicate balancing act. So melatonin is present at night when it's dark and dopamine is present during the day light hours.
"Researchers now suspect that under dim (typically indoor) lighting, the cycle is disrupted, with consequences for eye growth. “If our system does not get a strong enough diurnal rhythm, things go out of control,” says Ashby, who is now at the University of Canberra. “The system starts to get a bit noisy and noisy means that it just grows in its own irregular fashion.”"
I wonder, too, if the way we delay sleep for many many hours after melatonin production starts is also affecting our vision. Are kids staying up later? Is the iPad in bed (flashlight under the covers with a book) part of the problem as well? I wonder how adults are harming their eyes in the same way. More research required!