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Madjedi and colleagues examine the association of muscle-related measures (grip strength, thigh muscle volume measured, and self-reported walking pace) with glaucoma-related outcomes including: (1) prevalent glaucoma (per self-report or ICD-10 coding), (2) macular GCIPL thickness, and (3) IOP. Primary analyses were conducted in the UK Biobank cohort, with replication (using slightly different protocols) in the EPIC-Norfolk Eye Study. In both cohorts, stronger grip strength was associated with a lower prevalence of glaucoma in men, but not women. In the UK Biobank cohort, greater thigh muscle volume and self-reported walking pace were associated with a lower likelihood of glaucoma, but only in men. For OCT outcomes, both men and women with stronger grip strength had a thicker macular GCIPL layer, though only men with a faster self-reported walking pace had a thicker macular GCIPL layer. Neither men nor women showed associations with thigh muscle volume and macular GCIPL thickness. Noted associations were unlikely to be the result of IOP, as stronger grip strength was associated with slightly higher IOP in UK Biobank subjects, which would confer greater risk of glaucoma.
Observed effects were generally modest: a 1 SD increment in grip strength was associated with a 17% lower likelihood of prevalent glaucoma, and a <0.2 µm increment in macular GCIPL thickness. It is interesting that the authors were able to find (and replicate) their findings even when other population-based studies found no such associations (sometimes in unpublished results). It is possible that prior studies, by not stratifying analyses by gender, missed the associations noted here. As the authors note, it is also possible that the causation inferred is reversed – with glaucomatous vision loss resulting in deconditioning. Further work in longitudinal datasets would be useful to confirm and better gauge the causal relationship between muscle-related factors and glaucoma.