Vision Loss and Alzheimer's Disease: The Strange Connection

Diagnosing Alzheimer’s disease takes a very long and complex process, sometimes involving costly brain scans and surgical procedures. However, recent findings from a study conducted by Georgetown University Medical Center (GUMC) and the University of Hong Kong, presented at Neuroscience 2013, suggests that with simple eye tests, Alzheimer’s disease can possibly be diagnosed. ² This finding also suggests that there is a link between vision and Alzheimer's disease, which may also seem like two unrelated conditions. 

Two of the structures that are highly important for vision originate as outgrowths of the developing brain; these structures are the optic nerve and the retina. The retina has been the major focus of researchers linking changes in vision with the early detection and monitoring of Alzheimer’s disease.

Although the retina lines the eyeballs, it is still a part of the central nervous system. So, whatever causes the neurodegeneration of the brain cells will likewise cause the neurodegeneration of retinal cells. This connection forms the basis of the idea that the loss or reduction in the thickness of a certain layer of retinal cells may indicate the presence of Alzheimer’s disease and may be used to monitor its progression.

In contrast with the complex process that is currently being used in diagnosing Alzheimer’s disease, optical coherence tomography, which is a simple eye test, can easily be used to measure the thickness of the retina and, by extension, screen for the risk of Alzheimer’s disease. Arguably, the retina gives an early and easy sneak-peek into the brain to identify the risk of Alzheimer’s disease much earlier before it is full blown, and with an early diagnosis, the degeneration of brain cells can be halted and treated before it is too late.

Aside from the thickness of the retina, another connecting factor between vision loss and Alzheimer’s disease is a group of proteins, the beta-amyloids, which accumulate in the brain of Alzheimer’s disease patients. The presence of beta-amyloid plaques in the brain is the hallmark of Alzheimer’s disease. Deposition of these proteins has also been found to occur in the eyes, particularly in the lens during the early stages of Alzheimer’s and in the retina in cases of neurodegeneration of retinal cells.

Recently, a retinal imaging device was developed by NeuroVision Imaging at Cedars-Sinai; this diagnostic device can detect the presence of beta-amyloid proteins in the eyes of 15-20 years before clinical diagnosis can detect them in the brain.³ In preliminary studies, the optical imaging exam was found to be 100% specific and 80.6% sensitive for Alzheimer’s disease. In other words, everyone with Alzheimer’s disease tested positive with the device and almost everyone (80.6%) without Alzheimer’s tested negative. The researchers who tested this device presented their study at the Alzheimer's Association International Conference 2014 in Copenhagen, Denmark.