Retinal microvasculature in Alzheimer's disease.

Although cerebral small vessel disease has been implicated in the development of Alzheimer's disease (AD), the cerebral microcirculation is difficult to visualize directly in vivo. As the retina and the brain share similar embryological origin, anatomical features and physiological properties with the cerebral small vessels, the retinal vessels thus offer a unique and easily accessible "window" to study the correlates and consequences of cerebral small vessel diseases in vivo. Retinal microvasculature can now be visualized, quantified and monitored non-invasively using state-of-the-art retinal imaging technology. Recent clinic- and population-based studies have demonstrated a link between retinal vascular changes and dementia, in particular AD, and cerebral small vessel disease. In this review, we summarize the current findings on retinal vascular changes such as retinopathy signs and changes in novel retinal vascular network parameters and retinal vascular caliber with dementia, cognitive dysfunction and cerebral small vessel disease, and discuss possible future research to further evaluate whether retinal vascular imaging might help to elucidate vascular mechanisms contributing to the development of AD and provide additional value in predicting who may be at risk of developing AD.