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

To quantify anterior chamber depth (ACD) changes and identify associated determinants in individuals with good-corrected visual acuity. 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. 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). 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. Shallow anterior chamber depth is a major anatomical risk factor for primary angle-closure disease; however, longitudinal evidence on anterior chamber depth narrowing is limited. Anterior chamber depth narrows relatively faster at younger ages and the rate of narrowing slows after approximately 51 years. Younger age and shorter body height are associated with faster anterior chamber depth narrowing. Structural predisposition to angle-closure appears to be largely established by early middle age.