Local Variations in Rod Function and Subretinal Drusenoid Deposits (SDD) in Patients with Reticular Pseudodrusen (RPD)
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PURPOSE: Reduced rod sensitivity and slowed dark-adaptation are common in age-related macular degeneration, especially in those patients with reticular pseudodrusen (RPD). The unique fundus appearance in RPD is thought to be caused by subretinal drusenoid deposits (SDDs). In this prospective study, we evaluate the relationship between local variations in rod function and local variations in SDD thickness. METHODS: This study included one eye from each of six patients ages 59-89 with a best corrected visual acuity of 20/32 or better and one eye from each of 4 age-similar volunteers with healthy retinas. Following 30 minutes of dark adaptation, a 56 point macular scotopic sensitivity map was generated using short-wavelength, spot size 3 stimuli on a Nidek MP-1S fundus perimeter. For each patient, 8-12 roughly equidistant test points 4-8 degrees from the fovea were selected to represent areas of high and low scotopic sensitivity. Patients were exposed to a bright light for 3 minutes (80% bleach), and then these points were tested every 5-10 minutes over the course of 1.5-2 hours. SLO infrared images and SD-OCT volume scans (96 lines, 20*20 degrees), were acquired on a Heidelberg Spectralis imaging platform. Segmentation with manual adjustment was used to delineate the combined thickness of RPE and SDD. Segmentation results were then processed by a MATLAB routine to obtain the average RPE/SDD thickness of the 1 degree local area centered at each test location. RESULTS: The lowest sensitivity in the rod field was located in regions showing RPD on SLO fundus images, and correlated with RPE/SDD thickness (R2=0.21911). During dark adaptation, the time needed to gain 5 dB in sensitivity relative to the maximum luminance (recovery time) was longer in patients (mean=44.8 min) than in normals (mean=3.6 min, p<0.0001) and there was a significant correlation between SDD thickness and recovery time (R2=0.38135). DISCUSSION: Our results show that there are two separable consequences of SDD. One is to reduce dark-adapted sensitivity and the other is to substantially delay recovery from a bleaching light.