Longitudinal changes in retinotopic rod function in intermediate age-related macular degeneration

Abstract

Purpose : Rod photoreceptor function is known to be abnormal in early stages of age-related macular degeneration (AMD), however, retinotopic changes in rod function over time remain unclear. Our aim was to determine spatial-temporal changes in rod static and dynamic function in subjects with intermediate AMD.

Methods : Perimetric dark-adapted retinal sensitivities were performed at baseline and 12-month follow-up visit in 20 subjects with intermediate AMD and 6 healthy controls, using a Medmont Dark-Adapted Chromatic perimeter. At each visit, retinal sensitivities for the 505 nm stimulus across 7 retinal locations within the central 12° were repeatedly measured after exposing to a single photobleach. The sensitivities at 20 minutes after bleach were used to determine static rod function. Sensitivities at various times within the initial 20 minutes after bleach were used to estimate the rod criterion time (RCT, defined as the time taken to reach a rod threshold value of -3.0 log units stimulus intensity) to determine rod function dynamics. The changes in static and dynamic rod function over time were compared between AMD and control eyes.

Results : There was a significant reduction in average retinal sensitivity detected over the follow-up period in eyes with AMD (baseline = 45.3 ± 10.3 dB, 12m follow-up = 41.7 ± 11.7 dB, p = 0.01) but not in control eyes (57.9 ± 3.7 dB vs 57.0 ± 4.0 dB, p = 0.27). In eyes with AMD, there was a greater proportion of test points with declined RCT (25%) compared to the proportion of test points with improved RCT (6%, p <0.001). The majority of test points with declined RCT were located within the central 6° of the retina. There was no significant change in the RCT over time in the control eyes (6.3 ± 1.9 ms vs 6.3 ± 1.4 ms, p = 0.99). No changes were detected clinically during the follow-up period in both AMD and control eyes.

Conclusions : There are significant spatial-temporal changes in rod function within 12 months in eyes with intermediate AMD. Larger studies with a longer follow-up are required to determine whether these spatial-temporal changes in rod function are associated with AMD phenotypes and progression.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.