Abstract
Purpose :
Dysfunction in AMD is mostly a result of photoreceptor loss. Many clinical and adaptive optics optical coherence tomography (AO-OCT) investigators report reduced cone photoreceptors visibility over associated drusen. Two possibilities explanations are angular disorientation and cell structure disorganization. Our study uses directional OCT to measure contribution of these two factors, potentially guiding future research into early AMD.
Methods :
Three AMD subjects were recruited and dilated. Large drusen were identified using OCT images. The imaging beam was positioned at a series of horizontally displaced locations in the pupil, all imaging the same retinal location. 1200 B-scans of drusen and healthy adjacent retina were acquired at each pupil location. The apparent tissue slope indicates illumination angle. Between 20-50 cross-correlated B-scans were registered and averaged, producing one composite B-scan per subject, per retinal position. In each B-scan, abnormal and apparently-healthy tissues were delineated. Next, the inner-segment-outer-segment junction (ISOS) bands were segmented using a semi-automated procedure, resulting in a trace through both tissue types. Their reflectance and slope were computed at each A-scan in each B-scan. Separately for data from healthy and drusen-affected parts of ISOS segmentation, the relationship between slope and intensity was fit with a three-parameter (directionality 𝜌, non-directional component B, directional component A) Gaussian equation to quantify angle-dependent and independent components of ISOS reflectance. Healthy and drusen-affected retina were compared for each.
Results :
Between healthy and drusen-affected retina, large differences were found in parameters 𝜌 (p=0.011) and B (p=0.004), and small differences found in A (p=0.130). Values were lower in drusen-affected areas of retina than healthy for each.
Conclusions :
Reduction in fitted values of A and B values in drusen-affected tissue indicates gross attenuation of ISOS backscattered light. Reduction in 𝜌 indicates a widening of the acceptance angle of drusen-affected cones, suggesting changes in diameter and/or refractive indices of inner segment. Reduced reflectance and directionality of the inner-segment may underlie the low visibility of cones in adaptive optics imaging.
This is a 2021 ARVO Annual Meeting abstract.