(Journal of Clinical Investigation) Mounting evidence indicates that patients with AD and mild cognitive impairment (MCI) exhibit a wide spectrum of ocular abnormalities, circadian rhythm disturbances, and visual impairments. Among the many characteristics it shares with the brain, the retina contains neurons, astroglia, microglia, microvasculature with similar morphological and physiological properties, and a blood barrier. While the hallmark pathologies of AD have long been established in the brain, their manifestation in the human retina is a recent finding.