Interocular Differences in Visual Acuity and Refractive Status Between Unilateral Early and Late Age-Related Macular Degeneration: A Nationwide Population-Based Study.

Background/Objectives: Age-related macular degeneration (AMD) may affect the two eyes asymmetrically, but visual impairment is commonly classified by visual acuity (VA) in the better-seeing eye. We compared interocular-presenting VA differences in unilateral early versus late AMD, assessed the association between late AMD and worse VA in the AMD-affected eye, and compared refractive status between the affected and fellow eyes. Methods: We analyzed 1112 adults aged ≥40 years with unilateral AMD (1049 early and 63 late) from the 2017-2020 Korea National Health and Nutrition Examination Survey. Interocular VA difference was calculated as the logMAR VA of the AMD-affected eye minus that of the fellow eye. Survey-weighted modified Poisson regression estimated prevalence ratios (PRs), adjusting for age, sex, anisometropia, and the interocular difference in absolute spherical equivalent refraction. Exploratory analyses examined neovascular AMD and geographic atrophy separately, and sensitivity analyses assessed alternative model specifications. Results: Mean interocular differences were -0.004 logMAR (95% confidence interval [CI], -0.016 to 0.008) in early AMD and 0.184 logMAR (95% CI, 0.077 to 0.291) in late AMD. The weighted proportions with VA ≥ 0.2 logMAR worse in the AMD-affected eye were 10.15% and 58.31%, respectively. The adjusted PR for this outcome was 4.95 (95% CI, 3.46-7.09; p < 0.001) for late versus early AMD. Exploratory subtype-specific analyses showed similar associations for neovascular AMD and geographic atrophy. No statistically significant interocular differences in refractive status or astigmatism severity were detected; however, the wide 95% CIs, particularly in the late AMD group, precluded conclusions of equivalence. Conclusions: Unilateral late AMD was associated with greater interocular presenting VA asymmetry than early AMD, and the association remained consistent across sensitivity analyses. However, these cross-sectional findings do not establish longitudinal progression or directly demonstrate implications for spectacle prescribing or binocular visual function.