Behavioral and Structural Correlates of Axial Length in School-Aged Children: Baseline Findings from the Seoul Myopia Cohort Study.

Digital device use has substantially altered children's visual environments, yet the specific behaviors associated with axial elongation and early retinal remodeling remain unclear in highly urbanized settings. This study investigated biological and behavioral correlates of axial length (AL) and associated macular microstructural changes in preadolescent children. Participants underwent ophthalmic examinations and completed questionnaires assessing lifestyle and digital device use factors. Multivariable linear mixed-effects models identified factors associated with AL and macular thickness. The participant-level prevalence of myopia, defined as spherical equivalent ≤ -0.50 D, was 53.2% and increased from 37.1% in Grade 1 to a peak of 78.7% in Grade 4. Older age, a greater number of myopic parents, flatter corneal curvature, male sex, continuous smart device use exceeding 1 h per session, and viewing distance < 30 cm were independently associated with longer AL. Each 1 mm increase in AL was associated with significant subfoveal choroidal thinning and generalized extrafoveal macular thinning, whereas the central fovea remained relatively preserved. Pediatric AL was associated with hereditary susceptibility, specific digital viewing behaviors, and early extrafoveal retinal structural variation.