The progression of Alzheimer’s disease is significantly influenced by blood vessel abnormalities in the eye, according to a recent study conducted by experts from Cedars-Sinai. Published in the peer-reviewed journal Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association, the research reveals that these abnormalities correspond to changes in the brain, thereby offering a new possibility for early diagnosis of the disease.
The senior author of the study, Dr. Maya Koronyo-Hamaoui, who is a professor of Neurology, Neurosurgery, and Biomedical Sciences at Cedars-Sinai, explains that the research provides new insight into the vascular changes that occur in Alzheimer’s disease, especially in the retina, which is the layer of nerve tissue located at the back of the eye. The study also highlights the damage the disease causes to the blood vessels in the retina, providing a new, non-invasive pathway to early diagnosis and monitoring of disease progression.
The researchers compared blood vessels in retinas collected from 24 human donors with Alzheimer’s disease, ten donors with mild cognitive impairment, and 27 donors with normal cognition. They discovered that in patients with Alzheimer’s disease and mild cognitive impairment, there was a disruption of the blood-retinal barrier, which is where tightly joined cells prevent harmful substances from entering the retinal tissue.
In patients with Alzheimer’s disease, the deficit of this barrier was as much as 70%, meaning that harmful substances could pass through and enter the retinal tissue. This occurs very early on in patients with only mild functional impairment. The damage to the blood-retinal barrier was strongly linked to cerebral amyloid angiopathy (CAA), which is the accumulation of amyloid proteins in small blood vessels and other vascular diseases in the brain.
Currently, the only way to detect CAA in patients is through post-mortem brain tissue samples. However, with additional research and development of advanced retinal imaging, vascular and blood-retinal barrier damage could provide the first opportunity to detect CAA in living patients. The study also found that deposits of a protein called amyloid beta 40 accumulated in the retinal arteries of Alzheimer’s patients, making the arteries stiff, disrupting blood flow, and preventing the arteries from clearing harmful substances from the retina.
Further studies are necessary to determine whether the deposits accumulate due to blood vessel damage or actually cause the damage. Dr. Koronyo-Hamaoui explained, “Retinal and brain tissues are rich in blood vessels, and high blood supply is fundamental for their function. Restriction of blood supply, which may occur due to the damage we show happening here, means that these cells do not get the oxygen and the nutrients that they need.”
Advanced retinal imaging, which would look at the blood vessels and protein accumulation non-invasively in living patients, is currently in development. Still, it is not yet approved by the Food and Drug Administration. However, Dr. Koronyo-Hamaoui advises people to control their hypertension, eat a healthy diet low in sugar, reduce alcohol consumption, and avoid smoking to keep their circulatory system, including the blood vessels in the retina and the brain, healthy. This helps prevent chronic inflammation and damage to blood vessels, which according to the study, is a major element in the progression of Alzheimer’s disease.
In conclusion, the study adds to recent progress in advanced retinal imaging and the identification of other retinal biomarkers to advance the science of early detection of Alzheimer’s disease. Dr. Keith L. Black, the chair of the Department of Neurosurgery and the Ruth and Lawrence Harvey Chair in Neuroscience at Cedars-Sinai, explained that “as an anatomical extension of the brain, the retina has been extensively examined as a window to central nervous system disorders.” The knowledge gained from this study can be used to accelerate the development of new diagnostic tools and therapies to help in the fight against Alzheimer’s disease.