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Elaine Wells-Gray, Stacey S Choi, Nathan Doble; In Vivo Visualization of Cone and Rod Photoreceptors in the Healthy Human Retina using a combined AO-OCT-SLO. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4633.
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© ARVO (1962-2015); The Authors (2016-present)
Using a combined adaptive optics (AO) - optical coherence tomography - scanning laser ophthalmoscope (OCT-SLO) system, two distinct photoreceptor bands were observed close to the anterior surface of the RPE in healthy human eyes. This study tested the hypothesis that these bands correspond to distal portions of the cone and the rod outer segments, labeled as dCOS and dROS respectively.
The AO-OCT-SLO was used to image 2 human control subjects at 6°, 12°, and 18° in the temporal retina (TR). The OCT and AO systems use the same 860 nm SLD light source while the SLO uses a 680 nm imaging wavelength. The field of view for both modalities was 1.0° x 1.4°; with B-scans and SLO frames being acquired simultaneously at 60 Hz through a 7.15 mm exit pupil. Approximately 300-400 SLO frames and B-scans were acquired at each retinal location. The individual SLO and OCT images were post-processed to remove eye motion and averaged to increase the signal to noise ratio. Photoreceptors in the SLO images were used to help interpret the corresponding OCT B-scan structure. The photoreceptor layers in the B-scans were classified as either corresponding to a cone or a surrounding feature. Mean axial intensity plots were generated for both cell types, and analyzed.
Averaging over both subjects, at 6°, 12°, and 18° TR the mean cone inner segment (IS) lengths were 29.6 ± 0.1 µm, 25.9 ± 0.1 µm, and 24.3 ± 0.7 µm, and the cone outer segment (OS) lengths were 25.3 ± 0.8 µm, 22.0 ± 0.2 µm, and 19.9 ± 0.2 µm, respectively. The cone OS lengths showed greater variability than the IS lengths, and increased at higher eccentricities. Average OS length standard deviation was 2.3 ± 0.5 µm, 3.3 ± 0.9 µm, and 3.6 ± 1.2 µm, at 6°, 12°, and 18° TR, respectively.In between the larger cones, a distinct breakup of the photoreceptor structure in the OCT B-scan was observed with a bright intensity band believed to be the dROS lying posteriorly to the dCOS. The mean distance separating these two layers was 12.8 ± 0.5 µm, 21.0 ± 0.5 µm, and 20.5 ± 4.1 µm at 6°, 12°, and 18° TR, respectively.
Our results are consistent with our hypothesis that these layers do correspond to the dCOS and the dROS and are in agreement with histology data and other high resolution OCT reports. Further work is being performed to improve the visibility of the individual rods in the B-scans.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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