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Donald Thomas Miller, Zhuolin Liu, Omer Pars Kocaoglu, Kazuhiro Kurokawa, Ayoub Lassoued; AO-OCT imaging of photoreceptor loss across the transition zone in retinitis pigmentosa. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5113.
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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. While much is known about RP, the biological mechanisms that cause cones to die – the most debilitating phase of the disease – remains a longstanding mystery. To better elucidate photoreceptor loss dynamics in human subjects, we investigated the 3D reflectance profile of cones and rods across the transition zone between healthy and diseased retina in RP subjects using adaptive optics optical coherence tomography (AO-OCT).
We used the Indiana AO-OCT system at 500 KHz A-scan rate and clinical OCT (Spectralis, Heidelberg) to measure staging of RP progression in the photoreceptor layer. One subject with late onset adRP and one control were imaged. In both subjects, 450x450 µm2 AO-OCT volume videos were acquired along the horizontal meridian (1.5° to 7.5°), which sampled the transition zone as well as the healthy and severely diseased areas that straddled it. Volumes were registered to remove eye motion artifacts and segmented at the inner segment / outer segment junction (IS/OS), cone outer segment tip (COST), rod outer segment tip (ROST), and retinal pigment epithelium (RPE).
Spectralis B-scans along the horizontal meridian of the RP subject showed loss in the outer retinal bands that were staged with retinal eccentricity and indicative of the characteristic transition zone in RP. AO-OCT B-scans and averaged A-scans of the same meridian revealed dynamics in COST, IS/OS, ROST and RPE. COST reflection was lost first, then IS/OS. ROST was absent at all locations examined. In contrast in the normal subject, ROST increased 30% in reflectance while its axial distance from IS/OS decreased (42.2±1.2 to 39.2±0.5 µm) from 1.5° to 7.5°. From individual cone measurements, cone OS length was found significantly shorter in the RP subject compared to the normal for all retinal eccentricities examined. Surprisingly, even in the highly dystrophic location of 7.5° where cone OS banding was absent in the Spectralis image, a sparse array of cones was found with OS lengths about half that in the normal. Cone density was significantly reduced at all locations in the RP subject.
AO-OCT provides substantially more information about photoreceptor dystrophy in RP than commercial OCT.
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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