Abstract
Purpose :
Eyes with age-related macular degeneration (AMD) have been found to have a loss of rod photoreceptors in the parafovea, particularly at 4-5 degrees from the fovea. This can be observed functionally by a decline in sensitivity and adaptation to low light. The current study investigates dark adaptation in eyes with a range of AMD phenotypes to investigate the temporal and spatial gradients in dark adaptation.
Methods :
Dark adaptation kinetics were measured simultaneously in 8 retinal locations in one eye of 36 patients (age 53-88). Group 0 had no large drusen in either eye (n=10), Group 1 had large drusen in the study eye only (n=6), Group 2 had large drusen in both eyes (n=7), Group 3 had advanced AMD in the fellow eye and large drusen in the study eye (n=7), and Group RPD had reticular pseudodrusen (RPD) in the study eye (n=6). Following a 30% bleach, retinal sensitivity to a 1.8° 505 nm stimulus was measured every 3 min for 30 min at 8 retinal locations; 4, 6, 8, and 12 deg superior and inferior to the fovea. Rod intercept time (RIT; min), defined as the time required to detect a light at -3.1 log sc cd/m2, was derived from adaptation curves. RITslope (min/deg) was derived from the plot of RIT vs degree of eccentricity.
Results :
There was no significant effect of hemisphere on RITslope and thus data from corresponding eccentricities were combined for subsequent analysis. 8 of 72 RITslopes (Group 2, N=1; Group 3, N=2; RPD, N=5) were discounted from analysis because the patient did not adapt to -3.1 log sc cd/m2, at all eccentricities. There was a significant effect of AMD group on RITslope (P<0.0001). RITslope for Groups 2 (median = -0.91 min/deg; p<0.037) and 3 (-0.98 min/deg p<0.003) and RPD (-1.61 min/deg; p=0.025) was significantly different from controls (-0.22 min/deg). In looking at individual RIT values at different eccentricities, a two-way ANOVA found a significant effect of eccentricity (P<0.0001) but not AMD severity.
Conclusions :
RITslope, which measures spatial change in dark adaptation kinetics, increases with AMD severity and RPD. These results suggest that RITslope may provide additional information to that obtained from an RIT measure at a single eccentricity. These results also suggest RITslope may be a potentially useful outcome measure for functional studies of AMD.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.