Researchers in China found that spending an extra 40
minutes a day outdoors for three years resulted in a
reduction in the rate of myopia, or nearsightedness,
in children. Myopia is a condition in which close-up
objects can be seen clearly, but distant ones can't. It's
estimated to affect about half of kids in the U.S.
"Myopia has reached epidemic levels in China and...""
http://www.cbsnews.com/news/kids-exposed-to-more-sunlight-less-likely-to-need-glasses/