Retinal photoreceptor count, retinal surface area, and optic disc size in normal human eyes

The optic disc area of normal human eyes shows an interindividual variability of 1:7. This study evaluated whether the variation in the optic nerve head size is correlated with a variability in the retinal photoreceptor count and the retinal surface area.

Forty-six normal human donor eyes with an axial length of less than 26 mm were examined. The corneoscleral button, lens, and vitreous body were removed. The remaining cup of the eye was cut into orange slice-like pieces. Up to 25 retinal biopsies were taken from areas arranged in increasing distance from and concentric to the fovea. The photoreceptor outer segments were sonographically removed. The photoreceptor inner segments were counted on photographs taken from the outer side of the retina.

The count of the rods (mean +/- standard deviation: 57,447,000 +/- 10,481,000), the count of the cones (3,246,000 +/- 618,000), the optic disc size, and the retinal surface area (1204 +/- 184 mm2) were significantly (P < 0.05) and positively correlated with each other.

The results indicate that eyes with large optic nerve heads as compared with eyes with small optic discs may have a higher count of rods and cones and a larger retinal surface area. It corresponds with the positive correlation between the optic nerve fiber count and the optic disc size. Taking into account a loss of photoreceptors in glaucoma as recently reported, it may point toward a higher anatomic reserve capacity in glaucomatous eyes with large optic discs than in eyes with small optic nerve heads.