Abstract
Purpose :
Histological studies of the retina have shown that the axial properties of S-cones differ from their L/M counterparts. This study's purpose is to measure such differences in the living human retina using adaptive optics optical coherence tomography (AO-OCT).
Methods :
Two normal subjects were imaged at a retinal location 1° temporal to the fovea, selected because of its high S-cone density. Volumetric images subtending approximately 1° in lateral dimensions were acquired. B-scans were flattened to the predominant inner-outer segment junction (IS/OS) reflection and aligned with one another, and areal projections of that layer and underlying layers were generated.
Results :
Volumetric images contained quasi-hexagonally tiled, laterally distributed mosaics at the depths of IS/OS and cone outer segment tips, with appearance and spatial frequencies (75 - 80 cyc/deg) consistent with histological measurements of cone photoreceptor density. Most cones (>95%) contain a bright reflection at the predominant IS/OS depth, but some (<5%) possess a reflection 6 - 9 μm distal to it, with many of those lacking the predominant IS/OS reflection.
Conclusions :
These observations are consistent with a small minority of cones possessing a longer inner segment, which is observed in histological measurements of S-cones. However, many ambiguities persist. Some of the cones possessing the distally displaced IS/OS reflection also possess a reflection at the predominant IS/OS depth. The latter may be due to light blurred from neighboring cones. Alternatively, it may originate from the cone's IS/OS, with the distal reflection originating somewhere in the outer segment.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.