Adaptive Optics OCT-Based Drusen Grading for Assessing Severity of Dry Age-Related Macular Degeneration

Abstract

Purpose : Adaptive optics-optical coherence tomography-scanning laser ophthalmoscopy (AO-OCT-SLO) enables in-vivo imaging of single cone photoreceptors. From these images, cellular-level metrics can be developed to access the integrity of cones. Here, we analyze the retina of dry age-related macular degeneration (AMD) patients at and adjacent to drusen deposits. A novel drusen grading scale is presented based on changes in appearance of individual cone photoreceptors as a function of the underlying drusen height and width.

Methods : Fifty-seven drusen (height: 7–109 µm; width: 29-435 µm) within 4 degrees of the fovea from nine early-stage dry AMD patients were imaged with an AO-OCT-SLO system. A semi-automated algorithm was developed to identify cone microstructures, including the external limiting membrane (ELM), inner and outer segment junction (IS/OS) and the cone outer segment tip (COST). IS and OS lengths (ISL/OSL) were also calculated for each cone. Severity of drusen disruption was assessed based on a novel grading scale that identifies gaps in the IS/OS and COST layers. The grading scale ranged from 0 (normal photoreceptor structure) to 2 (extensive photoreceptor disruption) in 0.25 increments.

Results : Disruption of the IS/OS and COST layers increased with increasing druse height and width. COST disruption occurred before or concurrent to the IS/OS layer, with photoreceptors on average becoming fully disrupted (Grade 2) at a height of 89 µm or a width of 331 µm. The correlation (r) of drusen grade versus drusen height and width were 0.44 and 0.47 respectively. The OSL showed statistically greater shortening over drusen compared to ISL, 6.3% and 3.6% per 10 µm elevation respectively.

Conclusions : Photoreceptor-based metrics of abnormal pathology may serve as a biomarker to improve detection and monitoring of disease progression in dry AMD.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.