Age-indexed cumulative risk of high myopia estimated from axial length and early axial elongation: a 7-year school-based longitudinal cohort study

PurposeTo develop and validate age-indexed models estimating the cumulative risk of high myopia, defined as axial length (AL) ≥ 26.0 mm, using routinely collected ocular biometry, and to evaluate their potential for clinical risk stratification.MethodsThis 7-year school-based longitudinal cohort included 7,052 Chinese children aged 6–16 years at baseline who participated in a school-based screening program in Tianjin, China, from 2018 to 2024. Discrete-time survival models with age as the timescale estimated cumulative risk from ages 9 to 18 years. Two models were tested: baseline AL plus sex and baseline AL plus first-year axial elongation (ΔAL) plus sex. Performance was assessed in a participant-level temporal holdout test set using iAUC, iBrier, calibration, and decision-curve analysis, and by school-level internal-external cross-validation using iAUC and iBrier.ResultsOverall, 577 participants (8.2%) developed high myopia. In the temporal holdout test set (n = 5,245), the AL + ΔAL model outperformed the AL-only model, with higher discrimination [iAUC, 0.919 [95% CI, 0.902–0.933] vs. 0.851 [95% CI, 0.833–0.869]] and lower prediction error [iBrier, 0.074 [95% CI, 0.068–0.081] vs. 0.087 [95% CI, 0.080–0.095]]. Calibration was close to ideal, decision-curve analysis showed clinical net benefit, and school-level validation confirmed stable performance.ConclusionsRoutine AL measurement, particularly when combined with early axial elongation, enables accurate age-specific risk estimation of AL-defined high myopia and provides a transparent basis for timely and proportionate myopia-control decisions.