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Ravi Sankar Jonnal, Iwona Gorczynska, Justin V Migacz, Mehdi Azimipour, Robert J Zawadzki, John S Werner; Possible S-cone mosaic investigated with adaptive optics optical coherence tomography. Invest. Ophthalmol. Vis. Sci. 2017;58(8):308. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
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).
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.
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.
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.
Two projections of IS/OS at 1°. (Top left) The predominant IS/OS band in en face projection. (Top right) Corresponding en face projection 8 μm below the predominant band. Bright spots in the latter usually have corresponding dim spots in the former, which can be observed in the pseudocolor composite (bottom left). (Bottom right) The two subsets of cones--the majority that reflect at the predominant IS/OS band depth and the minority that reflect at the distal location--have different axial profiles, plotted here in red and blue, respectively. The blue axial profile is consistent with histological measurements of human S-cones. Scale bars 20 μm.
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