Nowadays, myopia has become a common phenomenon among children, and it seems to be a bit special not to have myopia instead. Some parents are also anxious that their glasses are frighteningly thick for their young age. There are many reasons for myopia, one of which perhaps no one is aware of – not being close enough to nature. Myopia is a common phenomenon today, but the high percentage of teenagers wearing glasses in this picture above is still surprising. In a recent article on myopia in the British journal Nature, it is mentioned that 60 years ago, the myopia rate in China was only 10-20% of the population, but today it is as high as 90% among teenagers. This is a common phenomenon in East Asia, where myopia is as high as 96.5 percent among 19-year-old males in Seoul, South Korea. The rest of the world has not escaped the plague of myopia. In the United States and Europe, about half of young people are affected by myopia, a percentage that has doubled compared to half a century ago. One study predicts that by about 2020, the number of people with myopia problems worldwide could reach 2.5 billion, about one-third of the total population. It seems that myopia is rapidly becoming a “global epidemic”, so what are the causes? Is myopia born of mom and dad? It’s true that there have been some studies showing a genetic link between myopia and myopia, with more than 100 places in the human genome mapping that have been found to be related to myopia. But genes obviously don’t tell everything. A study on Inuit showed that only 2 out of 131 elders were myopic, but more than half of their offspring were myopic, so there are obviously acquired environmental factors behind this. When it comes to environmental influences, it is easy to think of one culprit – desk work such as reading or writing homework. Indeed, there is data to support this, as East Asia is a region with a high prevalence of myopia, where children also spend more time reading and writing because of cultural and other reasons. A report by the Organization for Economic Cooperation shows that the average 15-year-old in Shanghai spends 14 hours a week on homework, compared with six hours in the United States and five hours in the United Kingdom. The same is true in Israel, where children who spend more time reading also have higher rates of myopia. Physiologically, spending too much time reading up close can lead to eye strain, which can lead to lesions and cause myopia. This seems to be a good explanation for the cause of myopia. Now here’s the fun part: In 2007, ophthalmologists at Ohio State University reported following 500 eight- and nine-year-olds who had normal vision at the start of the study, and five years later, one in five children had myopia. But the analysis showed that the number of books read per week, the number of hours read per week, and the amount of time spent on the computer, all factors that were thought to cause myopia, had no effect, and statistical analysis showed that the only environmental factor associated with the incidence of myopia was time spent outdoors. A year later, an Australian study came to the same conclusion. A follow-up study of 4,000 children in Sydney showed that those who spent less time outdoors had a higher chance of developing myopia. Is this really the case? The researchers analyzed the possible influencing factors one by one, such as children may be more active when they go outdoors, and the benefits of physical activity may reduce the incidence of myopia, but the analysis showed that exercise indoors did not have the effect of preventing myopia, indicating that the key is not in the exercise, but in the place. The analysis also showed that it did not matter what children did outdoors, whether it was sports, picnics, or even reading on the beach, as long as they spent more time outdoors, the incidence of myopia was lower. In addition, children who spend more time outdoors do not necessarily read fewer books. Some children read a lot of books but also spend a lot of time outdoors and do not end up nearsighted. What is the physiological explanation for this? One study suggests that staying indoors for long periods of time reduces the amount of light the eyes receive, which would have prompted the retina to release dopamine, and in the absence of light there is a lack of dopamine, leading to eye lesions. This theory is supported by animal studies with chickens, but some researchers do not think it is particularly convincing. Although other researchers have expressed reservations about the relationship between time spent outdoors and myopia, related applications have shown results in some places. In a study conducted in Guangzhou, children in six schools who were given an extra 40 minutes of outdoor time per day starting at age six or seven had 30 percent myopia by the time they were nine or ten years old, compared with 40 percent in the six other schools used as controls. In a similar trial in Taiwan, some schools allowed children to stay indoors or go outdoors during recess, while teachers in the schools tested required children to go outdoors for a total of 80 minutes after school. Clearly, there are many other benefits to children being outdoors besides helping to solve the myopia problem. On a sunny winter day, do you want to take your kids outside?