MAPT and early-onset autosomal dominant Alzheimer disease: When the fractal dimension of retinal vessels decreases, the sparse distribution of retinal vessels may represent the same alterations in the microvasculature of the brain (Nadal et al., 2020), indicating inadequate cerebral blood perfusion, which triggers activity in hypoxia-induced pathways that leads to pathological changes in tau, ultimately leading to the development and progression of cognitive impairment and even Alzheimer’s disease (Koike et al., 2011; Sabayan et al., 2012; Love and Miners, 2016).