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Alfredo Dubra, Yusufu Sulai, David R. Williams, Joseph Carroll; In Vivo Imaging Of The Rod Photoreceptor Mosaic. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5872.
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© ARVO (1962-2015); The Authors (2016-present)
The recent development of ophthalmic adaptive optics (AO) has allowed for non-invasive imaging of the cone photoreceptor mosaic outside the foveal center in the living retina. Here we demonstrate that with improved optical design and image registration, an AO scanning laser ophthalmoscope (AOSLO) is capable of resolving the cone and rod photoreceptor mosaics.
Sequences of images of the photoreceptor mosaic in 3 patients with blue cone monochromacy (BCM) and 2 normal subjects were recorded using a reflective AOSLO with astigmatism reduction in all pupil and retinal conjugate planes. Image speckle was minimized by using 680 or 796 nm superluminescent diodes with 8-10 nm bandwidths (FWHM) as light sources. The confocal apertures used to spatially filter the light before detection was approximately 0.55 and 1.1 Airy disks in diameter respectively. The recorded image sequences were registered to remove shift and distortion due to involuntary eye motion, and then averaged to increase signal-to-noise ratio. Cell locations within large areas of contiguous photoreceptor cells were used to estimate cell density and rod:cone ratio.
The rod photoreceptor mosaic was resolved at multiple retinal locations in both the BCM and the healthy subjects. The central-most foveal cones were also clearly resolved in the healthy subjects. The foveal cone mosaic in the BCM subjects show large dark areas, with very few bright spots we speculate correspond to swollen blue cone photoreceptors. The parafoveal rod-free zone can be clearly seen in the affected BCM patients, as previously shown by Carroll et al (ARVO 2010). The densities of rod photoreceptors in both normal and BCM subjects were consistent with those reported from histological studies, with the most dense rod mosaic being over 140,000 rods/mm2 at ~15 deg eccentricity.
An AOSLO with reduced pupil and image plane astigmatism, with a sub-Airy disk confocal aperture, can provide enough lateral resolution in the living human eye to fully resolve the rod and cone mosaics. Such a system could be used to quantitatively track cone and rod photoreceptor structure in patients with retinal disease, and may provide a means of early disease detection or an endpoint for pharmaceutical testing.
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