Simple myopia is the most common. Its incidence has been increasing in recent years around the world. In Western countries it used to be 25% of the population, but currently it can reach 40% in young people. In Asia, in countries such as China, Japan, Korea or Singapore, there is a percentage of more than 90% in the youth.
The risk factors are: the race (from more to less: Eastern, Caucasian, Black, Eskimo), the inheritance of parents, sex (more in women than in men), the educational level and certain occupations (microscopists, weavers , ...)
Therefore myopia depends on genetic and environmental factors. Genetics is relatively stable. Life habits have changed a lot in recent years: more work of close vision and more reading.
Until not long ago, myopia was very related to people who had a lot of activity in close vision, either for studies or for working. Now, many scientific papers have emerged that give a lot of importance to the light. We are increasingly spending less hours outside, with sunlight. We are most of the day with artificial lighting.
In a study conducted in Australia, it was found that white children were on the outside an average of 6h / day, those of Chinese origin, 4h / day. In China, in Beijing between 1-2h / day. In Singapore and Taiwan, among children of Chinese origin, 0.5h / day. The percentage of myopic young people was much higher in Chinese children in Singapore, Taiwan and Beijing than children of Chinese origin in Australia. In England, the average is 3-4h / day.
In a study by Jones et al. it was concluded that children who spend at least 15 hours a week (2.1h / day) outdoors have a 30% less risk of being myopic than those who are 5h a week (0.7 h / day). In another study by Sherwin et al, they calculated that every hour on the outside is 2% less likely to increase myopia.
To prevent myopia increase in children, more activity is advised on the outside. At the moment, too much is investigated in the peripheral blur. The glasses of myopia focus the image on the retina, but due to the optic of the eye, on the periphery of the retina there may be a slight defocusing behind. It has been seen that rising myopic is usually greater. At this time there are many ongoing studies with contact lenses that correct peripheral blur or with lenses of orto-k. It has been seen that the increase in myopia can be half that with glasses.