The Beijing Childhood Eye Study

Inclusion Criteria: 1) Currently enrolled students in grades 1-3 of the selected primary schools, in good health, with normal ocular appearance. 2) No ocular diseases, no strabismus, ocular trauma, or history of intraocular surgery, with unaided visual acuity of 20/20 or better. 3) Parental and student consent to participate in the survey and signed informed consent form. Exclusion Criteria: 1) Not currently enrolled in grades 1-3 of a primary school. 2) Students with pre-existing strabismus, other ocular diseases, or a history of ocular surgery at baseline, or those allergic to cycloplegic eyedrops. 3) Students unable to continue studying at their current school for more than three years from the baseline, including those who transfer to another school or withdraw from the study; 4) parental or student disagreement with participation in the survey.