Ocular biomarkers for early detection of Alzheimer's disease.

Alzheimer's disease (AD) is the most common form of dementia and is clinically characterized by a progressive decline in memory, learning, and executive functions, and neuropathologically characterized by the presence of cerebral amyloid deposits. Despite a century of research, there is still no cure or conclusive premortem diagnosis for the disease. A number of symptom-modifying drugs for AD have been developed, but their efficacy is minimal and short-lived. AD cognitive symptoms arise only after significant, irreversible neural deterioration has occurred; hence there is an urgent need to detect AD early, before the onset of cognitive symptoms. An accurate, early diagnostic test for AD would enable current and future treatments to be more effective, as well as contribute to the development of new treatments. While most AD related pathology occurs in the brain, the disease has also been reported to affect the eye, which is more accessible for imaging than the brain. AD-related proteins exist in the normal human eye and may produce ocular pathology in AD. There is some homology between the retinal and cerebral vasculatures and the retina also contains nerve cells and fibers that form a sensory extension of the brain. The eye is the only place in the body where vasculature or neural tissue is available for non-invasive optical imaging. This article presents a review of current literature on ocular morphology in AD and discusses the potential for an ocular-based screening test for AD.