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T. Chui, H. Song, A. Bradley, S. A. Burns; Local and Global Anisotropies in Cone Photoreceptor Packing. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3831.
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© ARVO (1962-2015); The Authors (2016-present)
To use high resolution retinal imaging to investigate local and global anisotropies in cone densities within the central retina of emmetropic adults.
A high resolution adaptive optics scanning laser ophthalmoscope (AOSLO) (bandwidth = 50nm) was used to image the cone photoreceptors of human eyes. Photoreceptor mosaics covering the entire central 9 mm2 of retina were obtained by using programmable displacements of scanning mirrors and careful fixation. Cone counts in a series of 100 x100 micron retinal areas sampled every 250 microns across the central retina were obtained using a custom Matlab program (MathWorks, Natick, MA). Local anisotropy (meridional variation in sampling within a local region) and global anisotropy (sampling differences across retinal meridians) in spacing of cone photoreceptor were studied by analyzing the Fourier power spectra at different retinal eccentricities along 90 degree, 135 degree, and 180 degree meridians.
Cone density was within the bandwidth of the imaging system for all the peri- and parafoveal regions, but cone counting was not possible in the central 0.5 degrees. Cone photoreceptor spacing was 8-15% larger in the radial direction than in the tangential direction at all eccentricities. Iso-eccentric samples obtained along the primary retinal meridians (90, 135 and 180) revealed a minor global anisotropy that was stable across eccentricity and revealed highest sampling density along the horizontal meridian.
Throughout the perifoveal and parafoveal retinal regions, our in vivo imaging reveals both local and global anisotropies similar to those reported for a single cadaver eye (Curcio and Sloan, 1992). These data support the psychophysical observations of higher VA along the horizontal meridian but are inconsistent with the standard oblique effect observed psychophysically within the central 18 degrees (Berkley et al., 1975; Rovamo et al., 1982).
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