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S.S. Choi, N. Doble, J. Christou, J. Plandowski, J. Enoch, D. Williams; In vivo imaging of the human rod photoreceptor mosaic . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2794.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:By increasing the resolution of retinal imaging systems, adaptive optics (AO) allows the routine in vivo imaging of the cone photoreceptors. However, the rod photoreceptors, which have inner segment diameters smaller than all but the smallest foveal cones, have never been resolved in images of living human retina. Our goal was to see if this imaging modality could be extended to visualize rods. Methods:The Rochester Adaptive Optics Ophthalmoscope was used to image photoreceptors at 5 and 10o eccentricities in the temporal retina on the horizontal meridian. Multiple images were taken with 550 and 670 nm light through a 6.8 mm pupil. These images were registered and summed to increase signal to noise ratio. Deconvolution was used to further enhance the image contrast. Results:For all 5 subjects, small, dim spots could be resolved between the larger, brighter cones in some, but not all, retinal locations. These faint spots could be distinguished from noise because they could be observed in repeated images of the same retinal location and their spacing and eccentricity dependence agreed with histological estimates of rod spacing (Curcio, 1990). Conclusions:Our results support the notion that adaptive optics imaging can occasionally resolve the smallest photoreceptors in the living human eye. The spacing between rod receptors in these retinal regions is about 2.8 microns which corresponds to a sampling frequency of about 105 cycles/deg. This is about half of 215 cycles/deg, the highest spatial frequency that can theoretically be resolved in an eye at this pupil size (6.8 mm) and wavelength (550 nm). Though the current imaging capability does not yet allow routine imaging of rods, future improvements could make it possible to image them in retinal disease.
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