The abundance of apoptotic cell markers, TUNEL and cleaved caspase-3, in the nuclei of retinal pericytes of both MCI and AD, and the correlations with PDGFRβ loss and Aβ40 burden, may indicate that some aspects of retinal vascular abnormality are linked with increased total Aβ40 burden in the retina. This evidence concerns the gene PDGFRB and Alzheimer disease.