Birth Year-Dependent Increase in Axial Length of Japanese Adult.

PURPOSE: To determine whether the correlations between the axial length and the aging-dependent and birth year-dependent age are significant. DESIGN: Retrospective cross-sectional study. METHODS: This study included Japanese patients ≥50 years who had undergone cataract surgery at numerous clinics from 2002 to 2020. Only 1 eye/patient was analyzed. The axial length was measured with the IOL Master. The age-dependent changes were determined by the significance of the correlation between the axial length and age by the birth year. The birth year-dependent changes were determined by the significance of the correlation between the axial length and birth year in the different age groups. The age refers to the age at the time of the cataract surgery. Spearman correlations were calculated. The turning points were identified by the LOESS, NLIN, and HPMIXED procedures. RESULTS: A total of 62,362 eyes (35,508 women, 26,854 men) were studied. The mean age was 72.9 ± 8.4 (standard deviation) years (range, 50-101 years), and the mean axial length was 23.90 ± 1.66 mm (standard deviation) (range, 19.20-37.07 mm). The birth year ranged from 1908 to 1970. Analyses of the birth year-dependent changes showed significant positive correlations in 48 of 81 (59.3%) groups for women and men. The increase in the axial length was birth year-dependent, and the turning point was 1939.4 for women and 1936.7 for men. CONCLUSIONS: The negative and significant correlation between the axial length and age is due to birth year-dependent changes. A birth year-dependent increase in axial length might have continued for several decades from the birth year of the late 1930s.