Alzheimer's disease and retinal neurodegeneration.

Alzheimer's disease (AD) is the major cause of dementia in the world. Although the entorhinal cortex and hippocampal complex are best known as the sites of early pathology in AD, increasing evidence shows that the eye, particularly the retina, is also affected. The AD-related changes in the retina are associated with degeneration and loss of neurons, reduction of the retinal nerve fibres, increase in optic disc cupping, retinal vascular tortusity and thinning, and visual functional impairment. Given the fact that evaluating pathologic changes in the brain during life has always been an indirect process, largely shielded from view by the barrier of the skull, the eye can be used as a window into diseases of the brain. Using modern techniques, the changes in the retina can be visualized in real-time. In addition to the changes in the eyes of AD patients, similar mechanisms of neurodegeneration in the brain have also been demonstrated in the eye. Targeting AD-liked changes in the retina has been recently shown to be effective in the reduction of retinal neuronal degeneration and loss in eye diseases. This review will cover recent findings on retinal degeneration in AD, pathological similarities between AD and eye diseases, and highlight the potential of modern technologies for the detection of prospective biomarkers in the eye in early AD.