COUNT AND DENSITY OF HUMAN RETINAL PHOTORECEPTORS

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 60123000 +/- 12907000, and mean cone count was 3173000 +/- 555000. Determined 40 mum away from the foveola, cone density measured 125500 cones/mm2. Extrapolating the distribution curve, cone concentration in the foveal center can be assumed to be about 150000 cells/mm2 to 180000 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 mum away from the foveola, it measured about 3.3 mum, and in the outer retinal regions about 10 mum. Rod density was highest in a ring-like area at a distance of about 3-5 mm from the foveola with a mean of 72246 +/- 17295 cells/mm2. Rod density peaked at 150000 rods/mm2. It decreased towards the retinal periphery to 30000-40000 rods/mm2. Rod diameter increased from 3 mum at the area with the highest rod density to 5.5 mum in the periphery. The hexagonal rod and cone inner segments were regularly arranged in a honeycomb fashion.