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Navjit Singh, Thomas Kane, Yesa Yang, James Tee, Melissa Kasilian, Angelos Kalitzeos, Michel Michaelides; Cone photoreceptor structure in RPGR-associated retinopathy. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4602.
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© ARVO (1962-2015); The Authors (2016-present)
Structural retinal imaging in individuals affected by RPGR-associated retinopathy has so far been limited to Optical Coherence Tomography. OCT performs well when looking cross-sectionally, however cannot resolve cones in the photoreceptor layer. In contrast, an Adaptive Optics Scanning Light Ophthalmoscope (AOSLO) can image cone mosaics in vivo at cellular resolution. We performed an observational, cross-sectional study employing AOSLO imaging to assess cone photoreceptor structure in subjects with Retinitis Pigmentosa associated with disease-causing variant in RPGR.
AOSLO imaging was performed in four patients as part of a natural history study (NCT03349242). The extent of the transition zone (TZ) was identified on OCT; this served as a guide for the AO imaging for each patient. An area that covered the entire TZ was captured at a 1° field of view. Both confocal (cone outer segments) and split detection (cone inner segment) videos were recorded in absolute spatial and temporal registration. Once the TZ was captured the images were processed and montaged. The anatomical foveal centre was then localized through the Peak Cone Density (PCD), and cone densities 1° away were counted in all four meridians.
Patient characteristics and density metrics are shown in Table 1. The PCDs measured ranged from: 29,218 – 49,671 cones/mm2 (mean±SD; 36,158±9,249 cones/mm2). From the split detection images, it was observed that the cones were generally larger in diameter than that of healthy individuals, while cone densities were also reduced. In addition, the wave guiding properties of the cones were affected, leading to poor or multi-modal reflectivity of the imaging light source. The extent of the TZ differed in patients, with the smallest having a diameter of ~2° and the largest of 4°.
We report novel data of the foveal and perifoveal cone mosaics of individuals affected by RPGR-associated retinopathy. Both inner and outer segments were resolved, leading to the calculation of PCDs and cone densities at 1° eccentricities in all four meridians. Cone densities were variable and did not correlate with age.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
AOSLO confocal (top row), contrast-stretched confocal (middle row) and split detection (bottom row) imaging modalities. All crops are taken at 1° superior from the centre. MM_0364 is an unaffected individual shown for comparison. Cone densities at this location are shown in Table 1. Crops are 85 microns wide (square).
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