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
A flood-illumination adaptive optics retinal camera was used to obtain images of the parafoveal cone mosaic in nineteen healthy volunteers. Cone density and spacing were estimated for each subject using a sampling window of 80 x 80 pixels, at 250-, 450-, 650- and 1100-um 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 1024x128 pixels image sections of the cone mosaic across the horizontal meridian from 200- to 1050-um 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% to 50% of cones were hexagonally arranged; the percentage of non-hexagonal Voronoi tiles increased at greater eccentricities.
Conclusions
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.
Keywords: 648 photoreceptors •
419 anatomy •
688 retina