Brain damage from Alzheimer’s disease can begin decades before patients show any symptoms, but a widely available eye exam shows promise for early detection.
A study published on August 23rd in the journal JAMA Ophthalmology describes how a non-invasive retinal exam successfully identified a sign of Alzheimer’s in patients who showed no traditional clinical symptoms. These patients exhibited significant thinning of the retinal center and degradation of the optic nerve, a finding noted by other researchers in those who have died of Alzheimer’s.
Participants in the study were primarily in their mid-70’s with no clinical symptoms of Alzheimer’s. Half of them had elevated levels of amyloid or tau, the two proteins associated with the disease as diagnosed through PET scans or lumbar punctures. During the study, researchers shined a light into the eye that allows the measurement of retinal thickness and fibers in the optic nerve. This test is widely available in ophthalmology offices. By combining it with angiography, doctors in the study could discriminate between participants’ red blood cells and other retinal tissue.
“The angiography component allows us to look at blood-flow patterns,” explained the co-principal investigator, Gregory P. Van Stavern, MD, a professor of ophthalmology and visual sciences. “In the patients whose PET scans and cerebrospinal fluid showed preclinical Alzheimer’s, the area at the center of the retina without blood vessels was significantly larger, suggesting less blood flow.”
The potential for identifying Alzheimer’s via an eye exam is exciting because current diagnostic techniques — PET scans and lumbar punctures — are invasive and expensive, making early detection less likely.
“This technique has great potential to become a screening tool that helps decide who should undergo more expensive and invasive testing for Alzheimer’s disease prior to the appearance of clinical symptoms,” said the study’s co-author, Bliss E. O’Bryhim, MD, PhD, a resident physician in the Department of Ophthalmology & Visual Sciences. “Our hope is to use this technique to understand who is accumulating abnormal proteins in the brain that may lead them to develop Alzheimer’s.”
The participants who tested negative for elevated amyloid or tau prior to the study did not show retinal thinning. Though additional research must be conducted, the study suggests a strong case for a reliable preclinical diagnosis of Alzheimer’s through an affordable, non-invasive eye exam.
Since people could have Alzheimer’s for decades before they begin to experience symptoms, the possibility of screening those in their 40’s and 50’s for the disease means treatment interventions might occur early enough to preserve patients’ quality of life for many years to come.
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