To investigate the principles influencing the occurrence and development of myopia by analyzing factors relevant to axial length growth in teenagers and children; to provide a basis for prevention and control of myopia.

In a prospective study, a stratified random sampling was used to select 12 middle schools and primary schools in the Shanghai Xuhui and Hongkou districts. The study enrolled 4 651 students, ranging in age from 6 to 13 years. Visual acuity, refractive error, axial length, and corneal curvature were tested and height and weight were recorded. A survey questionnaire that included information about the students' age, gender, family history, etc., was completed and follow-up surveys were repeated 2 times over a 2-year period. Census data were analyzed with a mixed model using SAS 9.3 software.

Axial length increased as a function of time. The coefficient estimate was 0.247, 0.491 (P< 0.01) . Variables such as gender, body mass index (BMI) , spherical equivalent (SE) , and an estimation of the average corneal curvature coefficient were- 0.307, 0.006, - 0.303, - 0.297, respectively (P<0.01) . For the age variable, the 6-year-old group was compared to the 7- to 13-year-old groups and the variable coefficient estimates were 0.115, 0.392, 0.471, 0.600, 0.816, 0.865, 0.909 (P<0.01) . For family history variables, parents were grouped as follows: neither parent was myopic, one was in the low or middle myopia group, one was in the high myopia group, both were in the low or middle myopia group, one was in the low or middle and one was in the high myopia group, both were in the high myopia group, coefficient estimates were 0.122, 0.257, 0.238, 0.429, 0.429, the differences were statistically significant (P<0.01) . The change in 2 years of axial length of right eye shows negative relation with the change in 2 years of SE.

In this population of teenagers and children, relevant findings revealed that axial length increases with time, age, BMI, family history, spherical equivalent, and average corneal curvature. Axial length increased gradually as age increased. The higher the BMI was, the faster the growth. The higher the degree of myopia in parents, the faster the growth. The higher the average corneal curvature was, the slower the axial length growth was. When the spherical equivalent was positive, a higher number corresponded with a slower growth in axial length. When the spherical equivalent was negative, a higher number corresponded with a faster growth in axial length.

Myopia; Axial length; Mixed model; Body mass index