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Ayoub Lassoued, Kazuhiro Kurokawa, Furu Zhang, James A. Crowell, Donald Thomas Miller; Unique adaptive optics OCT reflection in cone inner segments of subjects with retinitis pigmentosa. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1153. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Retinitis pigmentosa (RP) is the most common form of inherited irreversible visual loss worldwide. The biological mechanisms that cause cones to die–the most debilitating phase–remain unknown. To better describe photoreceptor loss, we used adaptive optics optical coherence tomography (AO-OCT) to characterize a subset of cones that unexpectedly present reflections from their inner segment.
We used the Indiana AO-OCT system at 500 KHz A-scan rate and clinical OCT (Spectralis, Heidelberg) to image three subjects: two with early and one with late stage arRP. 450x450 μm2 AO-OCT volume videos were acquired along the temporal horizontal meridian (early stage: 2°-12° and 3°-12° retinal eccentricity; late stage: 0.5°-4.5° retinal eccentricity), which sampled the transition zone as well as the healthy and severely diseased areas that straddled it. Volumes were registered in 3D to remove eye motion artifacts, projected separately along the cone inner and outer segments (IS, OS), and segmented to generate en face views of each. The inner segment / outer segment reflection was avoided in the projections. Cone ISs and OSs were manually identified in the images, their XY coordinates marked, and counts and densities determined at each retinal eccentricity.
Spectralis B-scans along the horizontal axis of the RP subjects confirmed loss in the outer retinal bands that is characteristic of a transition zone. As an expected result of cone degeneration, density of cone OS reflections in cones/mm2 decreased outwardly across the transition zone in all subjects: early-stage 1 (11,050 at 2° to 2,400 at 10°), early-stage 2 (11500 at 3° down to 2300 at 12°), and late-stage 1 (6800 at 0.5° to 2300 at 4.5°). In sharp contrast, density of IS reflections showed the opposite trend: early-stage 1 (650 at 2° to 5350 at 5.5°, then down to 2450 at 10°), early-stage 2 (800 at 3° to 2200 at 10°, then down to 1950 ), and late-stage 1 (3100 at 0.5° to 7050 at 2.5°, then down to 2450 at 4.5°). Most strikingly, we saw IS and OS reflections coinciding only in a few cones.
A new OCT reflection is discovered in cones in the transition zone of RP subjects. The reflection appears in the IS after disease progression destroys OS reflections and may indicate an intermediate stage of cone atrophy.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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