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Ayoub Lassoued, Zhuolin Liu, Kazuhiro Kurokawa, Jim Cromwell, Donald T Miller; Classification of cones across the transition zone in retinitis pigmentosa based on AO-OCT signature. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3226.
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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 in human retina, we developed a cone classification scheme based on the longitudinal reflectance profile of cones imaged with 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 image two subjects: one with late onset adRP and one control. 1.5°x1.5° AO-OCT volume videos were acquired at 1.5° to 7.5° temporal retina along the horizontal meridian, 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 cones were manually selected in the en face image. Based on the cross-sectional profile, cone outer segments (OSs) were classified as containing two or more reflections (interpreted as normal), containing one reflection (interpreted as degenerating at one tip), or containing no reflection (interpreted as degenerating at both tips). To capture the variability in OS morphology, standard deviations in 2-reflection cones’ OS length and axial center position were computed.
Spectralis B-scans along the horizontal meridian of the RP subject showed loss in the outer retinal bands that is characteristic of a transition zone. After examination of averaged A-scans over individual cones, normal OSs were found to constitute more than 89% of the total in the normal subject at any eccentricity, while in the RP subject, the percentage decreased with eccentricity from 77% at 1.5° to 0% at 7.5°. 2- reflection cones for the RP subject exhibited both a higher variation in the OS length (SD=4.5-8.7 μm) and center position (SD=0.5-3.3 μm) than for the normal subject (SD=2.3-4 μm and SD=0.1-0.4 μm respectively). The percentage of 1-reflection OSs was less than 9% at all locations in the normal retina; in the RP retina, it increased from 22% at 1.5° to 48% at 4.5° then decreased gradually thereafter. The percentage of 0-reflection OSs was less than 2% in the normal retina, while it increased from 0% at 1.5° to 63% at 7.5° in the RP subject.
AO-OCT reveals RP cone OSs to have reduced number of reflections and more varied length and axial location.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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