The Influence of Fellow Eye Status on Visual Function in Late AMD

Abstract

Purpose:: To investigate the influence of fellow eye status on psychophysical measures of cone and rod function in subjects with unilateral late AMD (geographic atrophy (GA) or choroidal neovascular membrane (CNVM)).

Methods:: Subjects with late AMD in one eye and VA better than 20/40 in the fellow eye (no diabetes, glaucoma or cataract) had their thresholds measured in the better eye for a 2° flickering (4Hz and 14Hz) or static isoluminant Red and Blue spots. Dark adaptation was also assessed following 30% pigment bleach with the time to rod-cone breack (RCB) being used for comparison. Testing was performed using a high-resolution CRT driven by 8-bit Radeon video-card (0-255 LUT) hosted in a Macintosh G4 computer. AMD stage was assessed using digital fundus photographs. The groups were compared with Mann-Whitney U test (alpha=0.05)

Results:: We found significantly larger defects in the fellow eyes of people from the GA (n=13) group compared with the CNVM (n=33) group for flicker (4 Hz; 0.03 ± 0.004 vs 0.06± 0.005; 14 Hz 0.04 ± 0.005 vs 0.06 ± 0.01) and red thresholds (0.03 ± 0.005 vs 0.05 ± 0.009); p <0.05. Blue thresholds failed to give a significant difference (0.21 ± 0.04 vs 0.42 ± 0.08; p=0.07) due to their larger variability. The RCB was not different between groups (19.4 ± 1.9 vs 20.6 ± 2.6 min; p = 0.74).

Conclusions:: This study suggests that cone mediated visual function could be affected differently by the atrophic macular degeneration form of AMD compared with the form that gives rise to choroidal neovascular membrane. This implies different etiologies for these two forms of AMD which may therefore benefit from the development of specifically targeted diagnostic tools and early interventions.

Keywords: age-related macular degeneration • retina • macula/fovea