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Rigmor C Baraas, Hilde Rogeberg Pedersen, Stuart J. Gilson; Foveal and parafoveal between-individual variation in in-vivo cone-to-RPE cell ratio. Invest. Ophthalmol. Vis. Sci. 2018;59(9):649.
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The retinal pigment epithelium (RPE) plays an essential role in the visual cycle and for maintaining a healthy retina. The metabolic load of RPE cells may implicitly be driven by the cone-to-RPE ratio within the macula. We hypothesize that differences in RPE cell density may vary less than cone density, both between-individuals and across foveal and parafoveal eccentricities, resulting in between-individual differences in cone-to-RPE ratios and metabolic load of single RPE cells.
Nine healthy males (3) and females (6), aged 21–65 yrs. were included in the study. High-resolution reflectance confocal, dark field and split-detector images were acquired with the Kongsberg AOSLO, a replica of that described by Dubra and Sulai[Biomed Opt Express 2011;2:1757–68], using 790 nm imaging light. SD-OCT and fundus autofluorescence images were acquired with the Heidelberg Spectralis OCT2. The registered and averaged images were scaled for individual retinal magnification factor based on the Liou and Brennan eye model calculated with Zemax software. Cone and RPE cells were identified via a semi-automatic algorithm at at least 12 retinal eccentricities along nasal-temporal (0–5 deg) and inferior-superior (0–3 deg) meridians to quantify RPE and cone density and cone-to-RPE ratio eccentricity dependence.
In the fovea, estimated cone and RPE cell density ranged from 105 500 to 207 200 and 8700 to 14800 cells/mm2, respectively. The cone-to-RPE cell ratio ranged from 8:1 to 21:1. There was no obvious relationship between cone density and RPE cell density. There was considerable between-individual variation in cone-to-RPE ratio decline with increasing eccentricity and the profile could not be characterized by a scalar factor that was consistent across eccentricities from 0 to 3 deg, but was more or less flat beyond 3 deg. The cone-to-RPE cell ratio ranged from 2:1 to 8:1 at 4–5 deg eccentricity.
The results are consistent with the hypothesis that there is less variation in RPE cell density than in cone density, resulting in considerable between-individual differences in cone-to-RPE ratios across the fovea-to-parafovea cell mosaics. Whether a high cone-to-RPE ratio and consequently a high RPE metabolic load results in higher susceptibility to RPE dysfunction requires further studies.
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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