"In the early 2000s, when researchers started to look at specific behaviours, such as books read per week or hours spent reading or using a computer, none seemed to be a major contributor to myopia risk. But another factor did. In 2007, Donald Mutti and his colleagues at the Ohio State University College of Optometry in Columbus reported the results of a study that tracked more than 500 eight- and nine-year-olds in California who started out with healthy vision. The team examined how the children spent their days, and “sort of as an afterthought at the time, we asked about sports and outdoorsy stuff”, says Mutti.
It was a good thing they did. After five years, one in five of the children had developed myopia, and the only environmental factor that was strongly associated with risk was time spent outdoors."
"Rose's team tried to eliminate any other explanations for this link — for example, that children outdoors were engaged in more physical activity and that this was having the beneficial effect. But time engaged in indoor sports had no such protective association; and time outdoors did, whether children had played sports, attended picnics or simply read on the beach. And children who spent more time outside were not necessarily spending less time with books, screens and close work. “We had these children who were doing both activities at very high levels and they didn't become myopic,” says Rose. Close work might still have some effect, but what seemed to matter most was the eye's exposure to bright light."
https://www.nature.com/news/the-myopia-boom-1.17120?fbclid=IwAR0V9DHZTpo0s-aFVYX...