BACKGROUND AND OBJECTIVE: To evaluate retinal microvascular changes in early and late-onset Alzheimer's disease (AD). PATIENTS AND METHODS: Eighty-six eyes of 50 late-onset AD participants, 27 eyes of 15 early onset AD participants, and 111 eyes of 57 cognitively normal controls were included. Optical coherence tomography angiography (OCTA) vessel density (VD) and perfusion density (PD) in Early Treatment Diabetic Retinopathy Study 3-mm and 6-mm circles and rings were assessed. RESULTS: There was decreased PD in early onset AD 3-mm circle ( P = .026) and ring ( P = .026) versus controls as well as in late-onset AD 3-mm circle ( P = .023) and ring ( P = .023) versus controls. There was decreased VD in late-onset AD 3-mm circle ( P = .012) and ring ( P = .006). No parameters differed between early and late-onset AD ( P > .05). CONCLUSIONS: AD eyes exhibited decreased retinal microvascular density compared to controls. Retinal parameters may not differ between early onset AD and late-onset AD after adjusting for age. [ Ophthalmic Surg Lasers Imaging Retina. 2021;52:336–344.]