AIM:To find out the prevalence of myopia among children and teenagers aged from 3 to 18 years in Qingyang District of Chengdu, and to provide evidence for the prevention and control of myopia.

METHODS: A cross-sectional study was designed. A total of 72 270 students, including 37 278 males(51.58%)and 34 992 females(48.42%), aged from 3 to 18 years old were screened in 38 schools in Qingyang District of Chengdu from October 2019 to January 2020, with an average age of(10.22±3.22)years old. The incidence of myopia, high myopia, anisometropia, refractive status and axial development were analyzed.

RESULTS: The incidence of myopia is 57.50%, high myopia 3.33%, moderate anisometropia 9.80%, and high anisometropia 4.24%. The age group between two adjacent two comparison: the myopia prevalence of 6-14 years old difference was statistically significant(all P<0.0033), high myopia incidence between 9-14 and 15-16 difference was statistically significant(all P<0.0033), the incidence of moderate anisometropia 7-11, 12 and 13 years old(all P<0.0033), high incidence of anisometropia, 5 and 6, and 8-12 years old(all P<0.0033). Axial length: the axial length of the right eye(23.658±1.258)mm, the left eye(23.611±1.246)mm, and the axial length of the left and right eyes between 5 and 18 years old showed statistical differences(all P<0.05), and the axial length of the right eye was longer than that of the left eye. The axial length of emmetropia and myopia of the eyes(take the right eye)in the same age group was statistically significant between the ages of 6 and 18(all P<0.01). The relationship between the refractive state and the axial length(right eye analysis): with the increase of age, the axial length increased, and the refractive index of the equivalent spherical mirror of hyperopia decreased gradually, and myopia increased gradually after emmetropia. The mean value of the equivalent spherical mirror(SE)was positive between 3-6 years old. From the age of 7, the mean value of SE turned to a negative value, presenting a myopic change, and the axial length was 22.923±0.759mm. Under different refractive conditions, the axial length was hyperopia as 22.489±0.853mm, and the emmetropia as 23.023±0.802mm, low myopia as 23.860±0.965mm, moderative myopia as 25.137±0.929mm, and high myopia as 26.252±1.040mm.

CONCLUSION: Compared with the past, the prevalence of myopia and the incidence of high myopia are on the rise. Prevention of myopia before the age of 7, and prevention of the development of high myopia should start at the age of 10. It is suggested that good eye hygiene habits should be formed before the age of 8 to prevent the occurrence and development of moderate and high refractive errors. Myopia changes at the age of 7, and myopia is more likely to occur in the right eye. We can predict the trend of myopia by axial length at different ages, and also assess the severity of myopia by axial length.