Optic nerves from ten patients with Alzheimer's disease were histologically examined and compared with those from age-matched controls. Specific and nonspecific measures of degeneration were noted in eight of ten Alzheimer's disease optic nerves; no degeneration was noted in any of the controls. Results of histologic examination of the retinas of one eye of three Alzheimer's disease patients also showed degeneration of retinal ganglion cells and their axons in the nerve fiber layer. Morphometric analysis suggested that in many cases of Alzheimer's disease, the optic nerve showed predominant loss of the largest class of retinal ganglion cells (M-cells) that contribute large caliber fibers to the optic nerve. The M-cell system is known to mediate specific visual functions, and selective involvement of the M-cell population leads to clinically measurable neuro-ophthalmic and psychophysical impairments in many Alzheimer's disease patients.