Correlation of the crystalline lens thickness and ocular parameters in young and middle-aged myopes grouped by axial length.

PURPOSE: To investigate the correlation between crystalline lens thickness (LT) and age, axial length (AL), anterior chamber depth (ACD), and vitreous length (VL) in myopic eyes stratified by AL. METHODS: This retrospective study included 458 myopic patients (95 males and 363 females). LT and AL were measured using the IOLMaster 500, while ACD was assessed with the Pentacam HR. Pearson correlation analysis was performed to evaluate the relationships between LT and age, AL, VL, and ACD in subgroups based on AL. RESULTS: The mean age was 28.41 ± 4.67 years and the mean spherical equivalent was − 7.71 ± 2.63 D. LT was positively correlated with age (r = 0.474, P < 0.001), and negatively correlated with ACD (r = − 0.378, P < 0.001) and VL (r = − 0.205, P < 0.001). The association between LT and AL varied across AL subgroups: in eyes with AL < 25 mm, LT was negatively correlated with AL (r = − 0.367, P < 0.001); the correlation weakened in eyes with 25 mm ≤ AL < 26 mm (r = − 0.156, P = 0.037); and no significant correlation was observed in eyes with 25 mm ≤ AL < 27 mm (both P > 0.05). Interestingly, in eyes with AL ≥ 28 mm, LT was positively correlated with AL (r = 0.263, P = 0.016). Segmented regression identified a biphasic relationship between LT and AL, with a breakpoint at AL = 26.7 mm (95% CI: 26.16–27.24 mm). CONCLUSIONS: LT exhibits a biphasic association with AL, suggesting that axial elongation beyond 26.7 mm may exceed the compensatory thinning capacity of the crystalline lens in myopic eyes.