Genetic factors are very important. The incidence of myopia is very high in China. If both parents are highly myopic, the genetic probability of children suffering from high myopia is basically above 90%.
The second is the acquired factor, which refers to long-term close contact and extensive use of eyes. Nowadays, children have little chance to look at the distance and spend a lot of time in contact with computers. Moreover, many children attend early education classes in advance and learn art, piano and painting from an early age. These activities require careful use of eyes, which takes a long time. Even if the child has no genetic factors of myopia, it is easy to cause myopia in adulthood.