The authors report the optical coherence tomography angiography (OCTA)-based comparative assessment of the retinal microvasculature in a rare pair of 96-year-old female monozygotic twins discordant for Alzheimer's disease (AD). Using automated mapping of the superficial capillary plexus, the authors observed that the twin with advanced AD had a significantly reduced vessel density and a larger foveal avascular zone in the superficial capillary plexus as well as a thinner choroid compared to the twin who was cognitively normal. This unique twin discordance report adds to the evidence supporting the use of retinal microvasculature changes in the superficial capillary plexus on OCTA as a possible noninvasive biomarker for AD. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:440-444.].