Count and density of human retinal photoreceptors

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Abstract
This investigation was directed at determining the count and regional distribution of photoreceptors in the eyes of 21 human cornea donors aged between 2 and 90 years. Mean count of rods was 60 123 000 ±12907000, and mean cone count was 3173000 ± 555000. Determined 40 μm away from the foveola, cone density measured 125 500 cones/mm2. Extrapolating the distribution curve, cone concentration in the foveal center can be assumed to be about 150 000 cells/mm2 to 180 000 cones/mm2. Towards the retinal periphery, cone density decreased from 6000 cones/mm2 at a distance of 1.5 mm from the fovea to 2500 cells/mm2 close to the ora serrata. Comparing different fundus regions, cone concentration was significantly highest in the nasal region. Cone diameter increased from the center towards the periphery. At a distance of 40 μm away from the foveola, it measured about 3.3 μm, and in the outer retinal regions about 10 μm Rod density was highest in a ring-like area at a distance of about 3–5 mm from the foveola with a mean of 72 246 ± 17 295 cells/mm2. Rod density peaked at 150 000 rods/mm2. It decreased towards the retinal periphery to 30 000–40 000 rods/mm2. Rod diameter increased from 3 μm at the area with the highest rod density to 5.5 μm in the periphery. The hexagonal rod and cone inner segments were regularly arranged in a honey-comb fashion.