What is the cause of myopia? Researchers in a country tracked more than 500 children aged 8-9 with normal vision. Five years later, they found that the only environmental factor related to myopia is the time children spend outdoors. Moreover, children's myopia is indeed related to the length of time they spend outdoors, whether they are exercising, having a picnic or just reading on the beach. 
A school requires children to go outdoors during the 80 minute recess every day and not stay indoors. One year later, 8% of the children were diagnosed with myopia, while the myopia rate of children of the same age in a nearby school was 18%
 the researchers believe that, The more important cause of myopia may be whether the eyes are in bright light, which can protect the eyes.