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Nicolas Chateau, Christophe Rondeau, Marine Durand, Nicolas Lefaudeux, Xavier Levecq, Michel Paques, Kate Grieve; Retinal pigment epithelium cell mosaic imaging across the macula with a modified flood-illumination adaptive optics camera. Invest. Ophthalmol. Vis. Sci. 2020;61(9):PB00131.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal pigment epithelium (RPE) cell mosaic can be resolved in the living retina using an adaptive optics (AO) system with transscleral illumination (TSI), as recently shown by Laforest et al. The present study evaluates RPE cell imaging across the macula with a conventional flood-illumination AO retinal camera modified by the addition of TSI.
An infrared LED projector was attached to AO retinal camera (rtx1-e, Imagine Eyes, France) in order to illuminate the retina with an 850 nm beam focused at the pars plana. It delivered 10 ms flashes at a rate of 20 Hz with an average power of 60 mW, while the camera acquired sequences of 40 AO images in 2 s. These images were averaged using publicly available software (TurboReg, EPFL, Switzerland). The procedure was performed repeatedly in the subjects' eyes, at multiple retinal locations across a 20x4 degree field. Cell visibility, optimal exposure, inter-cell spacing (ICS), and dependence on retinal eccentricity were analyzed.
3 healthy subjects aged between 22 and 25 years were examined. Circular cell-like structures with dark centers surrounded by brighter rings were visible in almost all images. At eccentricities beyond 5 degrees, cell-like structures were visible in the entire field of images obtained by averaging over 2 or 3 sequences (exposure time 4 or 6 s). At lower eccentricities, averaging 4 to 6 sequences (exposure time 8 to 12 s) was necessary to enable visualizing patches of cells within the images. ICS, when averaged across all eccentricities, ranged between 13.7 and 16.3 µm across subjects. In each retina, ICS was found to decrease by 15% typically between the outer macula and the fovea.
The implementation of TSI allowed visualization and quantification of the RPE cell mosaic in healthy subjects through relatively short acquisitions. RPE cells were more evenly visualized in the perifoveal and outer macular areas than in the fovea, the latter requiring double the exposure time. The quantitative results were compatible with previous morphometric assessments of the RPE mosaic. TSI could thus be a valuable addition to a conventional trans-pupillary flood-illumination AO camera.
This is a 2020 Imaging in the Eye Conference abstract.
RPE mosaic image acquired at 9 deg temporal, size 2x2 deg
Cell spacing represented as a function of eccentricity in 3 subjects (top) and on average in comparison with Tam et al.'s findings (bottom)
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