The myopia boom
My wife is co-authoring a review paper on this topic with the group from Zhongshan. The rise in myopia prevalence is really quite staggering, especially among asians.It's a long article, but the essential point is that insufficient time spent in bright light >10k lux (roughly corresponding to being in shade on a bright day) during early childhood increases the risk of developing myopia.Normal eye growth requires dopamine which is released in a circadian fashion, which requires exposure to bright/daylight. Absence of this dopamine cycle may cause the eyeball to be more elongated, leading to refractive errors.The precise number of hours needed to prevent myopia is difficult to say, but studies in schools with even 40-mins extra have shown benefit, and there's some evidence supporting 3+ hours/day.Importantly, it doesn't seem to matter how much close-focal work kids do, such as computer use/studying, as long as they spend sufficient time in bright light. I'd consider setting up a study desk in front of a large window, and taking breaks at school outdoors instead of inside.