Associations of incident myopia and its development with related factors among school-aged children across different grades: a four-year longitudinal study

To assess the progression of myopia across different academic grades and investigate the associations between potential myopia-related factors and the incidence of myopia at various grade levels.

We utilized data from an ongoing longitudinal study that began with grade 1 students across 12 schools. Four waves of annual eye examinations and questionnaire surveys were conducted. Longitudinal analyses were performed on three groups: Group 1 (n = 1223, non-myopic in grade 1) examined factors in grade 1 associated with incident myopia in grade 2; Group 2 (n = 653, non-myopic in grade 2) investigated factors in grade 2 related to incident myopia in grade 3; and Group 3 (n = 746, non-myopic in grade 3) evaluated factors in grade 3 associated with incident myopia in grade 4.

The incidence of myopia increased from 4.3% in grade 2 to 21.6% in grade 4. Our findings revealed a consistent positive association between the number of myopic parents and incident myopia in grades 2, 3, and 4, respectively. Outdoor activity in earlier grades showed significant protective effects, reducing the risk of incident myopia in the subsequent grades 2 and 3 (e.g., in Group 1, adjusted HR 0.46 [95% CI 0.24 ~ 0.86]). However, no significant association was observed between outdoor activity in grade 3 and incident myopia in grade 4.

It is important to consider the grade level of schoolchildren when addressing myopia control. Implementing early-phase interventions, particularly those emphasizing outdoor activities, may help mitigate the onset and progression of myopia during the earlier school years.