The size and shape of the optic disc in normal human eyes.

We studied the size, shape, and configuration of connective tissue of the optic disc in normal eye-bank eyes from 60 adults. The mean vertical and horizontal disc diameters were 1.88 and 1.77 mm, respectively. These figures are larger than most estimates of disc diameter using clinical image analysis methods. Within our sample, larger eyes did not have larger discs. The normal variation in disc diameter is sufficient to explain the normal variation in cup-disc ratio. The optic discs of blacks were larger and more oval than those of whites, though the axial lengths of the eyes in the two groups were not significantly different. Women's eyes and discs were smaller than those of men, possibly explaining the smaller cup-disc ratio in women. Larger optic discs and optic nerves have more optic nerve fibers than do smaller discs and nerves. Oblique insertions of the disc were detected in 18% of eyes. These were predominantly centered in the inferior disc and were more commin in white women.