Risk Factors for Adult Axial Length Elongation: A 5-Year Population-Based Cohort Study.

Purpose: Adult axial length (AL) elongation in adults is associated with pathologic outcomes; however, population-based longitudinal evidence remains limited, and pragmatic risk profiling is unclear. We aimed to quantify the prevalence and annual rate of AL elongation in adults and identify independent determinants in a population-based health-check cohort. Design: Retrospective, single-center cohort study. Subjects: A total of 4016 adults aged 22.4 to 93.0 years (8032 eyes; 21 421 visits) undergoing a Japanese health-check program, with a median follow-up of 5.31 years. Methods: For each eye, the annual AL change (mm/year) was estimated as the within-eye linear-regression slope and classified as severe (≥0.10), moderate (≥0.05 to <0.10), mild (≥0.00 to <0.05), or nil (<0). Associations were evaluated using a class-weighted proportional-odds ordinal logistic model. Pair-level change-point analysis modeled which eye elongated faster. Main Outcome Measures: Proportion of eyes by annual AL elongation severity, adjusted odds ratios (ORs) for determinants of more-severe elongation, and the baseline-AL intersection at which the longer eye becomes more likely to elongate faster. Results: Nil and mild accounted for 98.6% of eyes; moderate and severe were uncommon (1.3% and 0.2%). Independent determinants of greater severity included longer baseline AL (OR, 1.34 per 1 mm), larger interocular difference in AL (OR, 7.18 per 1 mm), myopic maculopathy including tessellated fundus (OR, 2.79), and female sex (OR, 3.05). Change-point analysis identified an intersection near 28.56 mm in the longer eye: below this value, the estimated probability that it would elongate faster was approximately 0.50 (no consistent lateral preference), whereas above it the probability exceeded 0.50 with wide uncertainty at high baseline AL values. Conclusions: Adult AL elongation is uncommon and slow; risk is concentrated in eyes with longer AL, greater axial asymmetry, myopic maculopathy, and in female adults. These readily measured features can inform follow-up decisions in health-check settings; pair-level estimates around 28.6 mm may help prioritize eyes for follow-up but should be interpreted cautiously. Financial Disclosures: Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.