Abstract
Purpose :
New clinical-grade, high-resolution optical coherence tomography (OCT) with significantly increased axial resolution reveals a splitting of the hyperreflective band at the interdigitation-zone, presumably coinciding with the rod and cone outer segments tips (cone outer segments [COS] and rod outer segments [ROS]). The aim of this study was to investigate whether the thickness and intensity of these bands correspond to rod and cone photoreceptor (PR) density.
Methods :
Five eyes of five subjects (22, 29, 33, 45, 67 years; 2 females) were imaged using adaptive optics scanning laser ophthalmoscopy at 0.5 mm (transition from cone- to rod-dominated retina), 1 mm and 2 mm temporally from the fovea. High resolution OCT volume scans (High-Res OCT, Spectralis, Heidelberg Engineering, 121 B-scans, 30X25 mm, ART=25) were semi-automatically annotated, converted to enface maps and the thickness and intensity profiles (normalized to Bruch’s membrane) extracted for the corresponding locations. These profiles were statistically analyzed using separate linear regression models for both rod and cones densities.
Results :
Cone PR density was highest at 0.5 mm (42,083 ± 3,960 cones/mm2) and decreased peripherally (2 mm: 11,748 ± 926 cones/mm2). In parallel, COS thickness (27 ± 3 to 20 ± 3 µm) and maximum intensity (90->62%) decreased. In contrast, rod density was lowest at 0.5 mm (38,056 ± 4,137 cones/mm2) and increased at higher eccentricities (2 mm: 96,914 ± 8,479 rods/mm2), while ROS thickness (3 ± 4 to 16 ± 3) and maximum intensity (20% -> 64%) showed a similar increase. The regression analysis for rods indicated a significant positive relationship between rod density and ROS, with an increase of 1 micrometer in thickness for additional 2,512 rods per square millimeter (p = <0.01), explaining 42% of the variance (Intensity: p = 0.13, R2 = 0.16). Cone density was similarly related to COS (Thickness: p =< 0.01, R2 = 0.47 / Intensity: p = 0.02, R2 = 0.3).
Conclusions :
Results indicate a correspondence between high resolution OCT-derived ROS and COS measurements and AOSLO-derived PR densities, allowing for a fast and selective quantification of PRs using routine clinical imaging techniques. These findings will guide our future research if the COS and ROS microstructure can be utilized to track loss of PR and whether retinal microstructure can reflect rod and cone function with age and disease.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.