The normal human optic nerve. Axon count and axon diameter distribution.

Computerized image analysis was used to determine the normal axonal count and axon diameter distribution in 12 normal human eyes. Mean axon count per nerve was 969,279 +/- 239,740 and mean axon diameter was 0.72 +/- 0.07 micron. Multiple linear regression disclosed 4909 axons lost yearly (P = 0.08). Statistical analysis did not show a relationship between axon diameter and age or time to fixation. The inferotemporal sector of the nerve had the highest fiber density (P = 0.02). The superonasal nerve had higher mean diameters (P = 0.02). This study may provide a baseline for future pathologic studies.