Genetics influence a person’s risk of developing myopia, but much of the increase in the past few decades is related to environmental factors. A 2015 study (via PLoS One) discovered that people are more likely to develop myopia if they perform more activities from a short distance (“near work”), such as writing, reading, studying, playing video games, or watching television. Myopia is particularly prevalent among highly educated people who spend a lot of time reading, studying, and writing.
Another contributing factor is the amount of time a person spends inside, which often goes hand in hand with the amount of “near work” they perform. The World Health Organization attributes much of the increase in nearsightedness in East Asia to intensive education and time spent indoors.
According to the NEI, the best way to prevent myopia is to spend more time outdoors. The NEI notes that after Taiwan incorporated more outdoor time into its school curriculum, fewer children developed nearsightedness. This is one of many reasons why it is important for children to get outside and play.