Eye test may predict Alzheimer's disease risk
An eye examination provides an opportunity to obtain a detailed look at the blood vessels of the retina. The primary neuropathological (brain pathology) hallmark of Alzheimer’s disease is the presence of amyloid deposits (plaques) in the blood vessels of the brain. Researchers in Perth, Australia have determined changes in blood vessels that may serve as an early warning that Alzheimer’s disease is likely to develop. Their hope is that by detecting early changes in these vessels can lead to interventions that can delay or prevent the development of Alzheimer’s disease. They published their findings online on February 26 in the journal Translational Psychiatry.
The researchers note that the buildup of amyloid deposits in the brain leads to cerebral (cortical and particularly hippocampal) atrophy and is identified clinically by a progressive decline in memory, learning and executive function. They note that a post-mortem (autopsy) examination of the brain is required for confirmation of Alzheimer’s disease; however, a diagnosis of probable Alzheimer’s disease can be made in patients, fulfilling the criteria set down by the National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer’s Disease and Related Disorders Association.
The investigators explain that currently, a diagnosis of probable Alzheimer’s disease is only possible when the condition has progressed, and considerable neurological damage has already occurred. Alzheimer’s disease has an increasing prevalence around the globe and an urgent need exists to treat the condition before the brain is irreversibly damaged; thus, a sensitive and specific screening technology is needed to identify high-risk individuals before cognitive symptoms arise. They note that current treatments are limited in their efficacy; however, earlier detection of Alzheimer’s disease would assist the development of interventions aimed at preventing or delaying the neurodegenerative process, and could contribute to development and evaluation of new treatments.
PiB-positron emission tomography (PiB-PET) imaging and the presence of amyloid in the cerebral spinal fluid are currently the best method for early diagnosis of the disease; however, there are practical limitations for population screening. A PET scan is a radiology procedure that costs between $3,000 and $6,000. To check the cerebrospinal fluid for amyloid requires a spinal tap. Alzheimer’s disease-related pathology occurs primarily in the brain; however, some indicators of the disease have also been shown to occur in other tissues, including the retina, which is more accessible for imaging. The authors note that retinal vascular changes and degeneration have previously been reported in Alzheimer’s disease using optical coherence tomography and laser Doppler techniques. They explain that their study presents results from analysis of retinal photographs from Alzheimer’s disease and healthy control participants from the Australian Imaging, Biomarkers and Lifestyle (AIBL) Flagship Study of Ageing. They note that their study is the first to investigate retinal blood vessel changes with respect to amyloid plaque burden in the brain.
The researchers demonstrated relationships between retinal vascular parameters, neocortical brain amyloid plaque burden, and Alzheimer’s disease. They found that a number of retinal vascular parameters were found to be different in Alzheimer’s disease. They also found that two of these parameters, venular branching asymmetry factor and arteriolar length-to-diameter ratio, were also higher in healthy individuals with high plaque burden. They concluded that retinal photographic analysis has a potential as an adjunct for early detection of Alzheimer’s disease or monitoring progression or response of the disease to treatments.
Reference: Translational Psychiatry