Eccentricity dependent changes of density, spacing and packing arrangement of parafoveal cones

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Abstract

Purpose

To investigate the distribution of cone density and spacing as well as the preferred packing arrangement of the cone mosaic as a function of retinal eccentricity.

Methods

An adaptive optics retinal camera (rtx1, www.imagine-eyes.com) was used to obtain images of the parafoveal cone mosaic in nineteen healthy volunteers. Cone density and spacing were estimated for each subject (both eyes) using a sampling window of 80 × 80 pixels, at 250-, 450-, 650- and 1100-μm eccentricities from the fovea along the nasal and temporal retina of both eyes. The inter-subject and intra-subject variation of cone density and spacing were calculated via Coefficient of Variation (CoV). Cone packing arrangement was assessed using Voronoi analysis; calculations were done over 1024 × 128 pixels image sections of the cone mosaic across the horizontal meridian from 200- to 1050-μm eccentricities.

Results

The inter-subject variation of parafoveal cone density ranged between 10% and 15% (p < 0.001) and the intra-subject variation of cone density was lower than 8% in all subjects, except for two. The cone spacing values showed a moderate inter-subject (CoV<7%; p < 0.001) and a low intra-subject variation (CoV<4% in all subjects, except for two cases). In the parafoveal region, 40–50% of cones were hexagonally arranged; the percentage of non-hexagonal Voronoi tiles increased at greater eccentricities.

Conclusion

The use of multiple and complementary metric descriptors allows for a more detailed description of packing distribution and preferred arrangement of cone photoreceptors across the parafoveal retina.

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