Corneal contribution and internal compensation in astigmatic development in preschool children: a population-based study

To characterize the distribution, biometric associations, and compensatory patterns of refractive astigmatism (RA), corneal astigmatism (CA), and internal astigmatism (IA) in preschool children, and to evaluate their relationships with spherical equivalent refraction (SE), axial length (AL), and axial length-to-corneal radius ratio (AL/CR). In this population-based study conducted in Tongzhou District, Beijing, children aged 3–6 years from nine kindergartens underwent cycloplegic autorefraction and ocular biometry. Astigmatism prevalence was calculated using multiple thresholds. Associations between astigmatic components and ocular biometric parameters were analyzed using logistic regression, Spearman correlation, and nonlinear curve-fitting models. Among 1,515 eligible children, 1,410 (93.1%) completed examinations (mean age, 4.44 ± 0.82 years; 51.9% boys). Mean (± SD) SE was 1.23 ± 0.72 D. RA prevalence was lower than CA and IA. RA and CA showed U-shaped relationships with SE, with minimal values occurring within a mildly hyperopic range. IA showed comparatively little variation across SE. RA, CA and IA were inversely associated with AL. Although exploratory quadratic models for AL/CR had limited explanatory power, the observed distribution patterns suggested that RA and CA tended to increase when AL/CR deviated from the 2.7–2.8 interval. CA exhibited greater variation than IA. Under-compensation was the most common pattern (J 0 : 53.82%; J 45 : 31.07%). RA and CA showed U-shaped cross-sectional associations with SE, whereas IA varied comparatively little across SE categories. CA showed greater variation than IA in relation to SE, AL, and AL/CR, while IA partially compensated for CA, with compensation patterns differing between J 0 and J 45 .