Relationships of Body Composition with Refractive Error and Axial Length in 8-Year-Old Japanese Children

Objectives: This study aimed to examine the relationships between refractive error and axial length (AL) and body composition parameters, including obesity-related indices, in 8-year-old children enrolled in the Japan Environment and Children's Study (JECS). Methods: From 2019 to 2022, data from the right eyes of 1866 children aged 8 years enrolled in the JECS adjunct study were analyzed. AL, noncycloplegic spherical equivalent (SE), and uncorrected visual acuity were measured. Relationships of these ocular parameters with height, weight, muscle mass, body fat percentage, the Rohrer index, and sex were evaluated. Results: The mean AL was 23.09 mm, and the mean SE was -0.52 D in the right eye. Despite the correlations of the Rohrer index with SE (r = 0.05, p = 0.02), uncorrected visual acuity expressed as logMAR (r = -0.07, p = 0.005) and AL (r = -0.06, p = 0.02) reached nominal statistical significance, and all correlation coefficients were close to zero, indicating no meaningful linear correlations. SE and logMAR showed no meaningful correlations with height, weight, muscle mass, or body fat percentage. AL showed small positive correlations with height (r = 0.17, p < 0.001) and muscle mass (r = 0.14, p < 0.001); its correlation with weight was negligible (r = 0.07, p = 0.004), and no meaningful correlation was observed with body fat percentage. Conclusions: Among 8-year-old children, the Rohrer index showed no meaningful linear correlation with refractive error, uncorrected visual acuity, or AL despite having nominally significant p-values. AL showed small positive correlations with height and muscle mass, suggesting a limited cross-sectional relationship with overall somatic size; however, the small effect sizes preclude strong conclusions. Because refraction was measured without cycloplegia, the SE findings should be interpreted cautiously, as accommodation may have shifted measurements in the myopic direction.