Body size has been closely linked to primary open-angle glaucoma (POAG). However, the association was inconsistent, which may be due to the fact that body size defined by body mass index does not differentiate fat from lean mass or capture body composition distribution. The impact of body composition on POAG remains largely unknown.

Combined cross-sectional and cohort study.

A total of 88,123 participants and 291,983 participants from the UK Biobank for the analysis of baseline intraocular pressure (IOP) and POAG incidence, respectively.

Fat and muscle mass in the arm, trunk, and leg were estimated using bioimpedance analysis. Measurements were normalized for height to derive the arm fat index, trunk fat index, leg fat index (LFI), arm muscle index, trunk muscle index, and leg muscle index. Fat-to-muscle ratios for each region were also calculated as sensitivity analysis. Hazard ratios (HRs) and 95% confidence intervals (CIs) for POAG were estimated using covariate-adjusted Cox models, and associations with IOP were additionally assessed using linear regression.

Baseline IOP and POAG incidence.

Greater leg fat was associated with a significantly reduced risk of POAG, supported by both LFI (HR, 0.85; 95% CI, 0.76-0.95; P  = .006) and leg fat-to-muscle ratio (HR, 0.35; 95% CI, 0.16-0.73; P  = .005). No association was observed between muscle mass and the incidence of POAG. Greater fat mass was associated with higher IOP levels, supported by arm fat index ( β , 0.14; 95% CI, 0.07-0.22, P < .001), LFI ( β , 0.15; 95% CI, 0.11-0.18, P < .001), trunk fat index ( β , 0.07; 95% CI, 0.04-0.09, P < .001), whereas greater muscle mass in leg (leg muscle index: β , –0.24; 95% CI, –0.29 to –0.20, P < .001) and trunk (trunk muscle index: β , –0.05; 95% CI, –0.08 to –0.01, P  = .005) was associated with lower IOP.

POAG risk differs according to body composition. Maintaining a healthy body composition pattern may mitigate its risk.