Ge YJ, Xu W, Ou YN, et al. - Through systematically searching PubMed, EMBASE, Scopus, and Web of Science from inception to January 2021 for observational studies, researchers sought to localize candidate retinal biomarkers in Alzheimer disease (AD), mild cognitive impairment (MCI), and preclinical AD. There were 126 articles eligible for inclusion out of the 19,727 citations found. When compared with healthy controls, the thickness of peripapillary retinal nerve fiber layer, total macular, and subfoveal choroid were significantly reduced in AD patients. In addition, patients with MCI had lower thickness of peripapillary retinal nerve fiber layer, total macular, and subfoveal choroid compared with healthy controls. Retinal structural, vascular, and electrophysiological biomarkers have enormous potential for use in the diagnosis, prognosis, and risk assessment of AD and MCI. Such biomarkers should be developed further in the future, particularly in diagnostic test accuracy and longitudinal studies.