Histologic studies were carried out on 300 optic nerves covering ages from birth to 96 years. The optic nerve is small and nearly unmyelinated at birth. It rapidly grows and becomes medullated. With advancing years, the leptomeninges and fibrous septa become broader and occupy an increasingly larger proportion of the cross-sectional area of the nerve. The axons progressively diminish, and this probably reflects primarily a loss of ganglion cells and would contribute considerably to reduced visual acuity in the older population. Other age-associated degenerative changes are corpora amylacea and lipofuscin in astrocytic cytoplasm. In the older population, scars, swollen axons, and Schnabel's cavernous degeneration become common, indicating a high incidence of vascular impairment.