Impaired mesopic visual acuity in eyes with early age-related macular degeneration.

PURPOSE To determine photopic and mesopic distance high-contrast visual acuity (HC-VA) and low-contrast visual acuity (LC-VA) in eyes with early age-related macular degeneration (AMD). METHODS Measurements were made in 22 subjects with early AMD and 28 healthy control subjects. Inclusion criteria included a photopic HC-VA of 20/25 or better. Distance VA was measured using HC (96%) and LC (10%) Bailey-Lovie logMAR letter charts under photopic (85 cd/m(2)) and mesopic (0.1-0.2 cd/m(2)) luminance conditions. RESULTS Mean mesopic distance HC-VA and LC-VA were significantly worse (0.1 logMAR and 0.28 logMAR, respectively) in the early AMD group than in the control group. Under mesopic conditions, the mean difference between LC-VA and HC-VA was significantly greater in the early AMD (0.45 logMAR) than the control group (0.27 logMAR). Mean differences between mesopic versus photopic HC-VA and mesopic versus photopic LC-VA were significantly greater in the early AMD than the control group (0.13 and 0.32 logMAR of difference between the means, respectively). Sensitivity and specificity were significantly greater for mesopic LC-VA than for mesopic HC-VA (Receiver Operating Characteristics, area under the curve [AUC], 0.94 ± 0.030 and 0.76 ± 0.067, respectively). AUC values for photopic HC-VA and LC-VA were below 0.70. CONCLUSIONS Visual acuity testing under low luminance conditions emerged as an optimal quantitative measure of retinal function in early AMD.