Longitudinal change in anterior chamber depth and its determinants: a median 4.9-year follow-up of 2,247 Japanese adults

Purpose: To quantify anterior chamber depth (ACD) changes and identify associated determinants in individuals with good-corrected visual acuity. Methods: In a retrospective single‑centre cohort, participants attending a combined health and eye screening programme underwent same‑day biometry, anthropometry and routine haematology. For each participant, the annual ACD change (mm/year) was estimated as the individual-linear regression slope. The cross-sectional age–ACD relationship was characterised with restricted cubic splines and a single-knot piecewise model. Associations between annual ACD change and baseline characteristics were evaluated using ordinal logistic regression across quartiles of the slopes. Results: A total of 2,247 participants (median age at baseline visit 52.7 years) with 10,869 visits over a median follow-up of 4.9 years were analysed. The median annual ACD change was − 1.11 × 10⁻² mm/year (interquartile range − 2.04 × 10⁻² to − 0.24 × 10⁻²). The piecewise model identified a knot at 51.3 years, with estimated ACD narrowing of − 1.52 × 10⁻² mm/year at ages ≤ 51.3 and − 0.91 × 10⁻² mm/year at > 51.3 (both P < 0.001). Ordinal models showed that younger age and shorter body height were associated with faster ACD narrowing (both P < 0.05). Conclusion: ACD narrowing progressed more steeply until approximately 51 years of age, with a trend toward relatively faster narrowing in shorter individuals. These findings suggest that structural predisposition to angle-closure is largely established by early middle age and support targeted monitoring and preventive strategies in middle-aged, shorter adults.