It may be possible in the future to screen patients for Alzheimer’s disease using an eye exam.
In a new study, researchers from Washington University used technology similar to what is found in many eye doctors’ offices to detect Alzheimer’s in older patients who had no symptoms of the disease.
Brain damage from Alzheimer’s disease can occur years before any symptoms such as memory loss and cognitive decline appear.
Scientists estimate that Alzheimer’s-related plaques can build up in the brain two decades before the onset of symptoms, and they have been looking for ways to detect the disease sooner.
Doctors now use PET scans and lumbar punctures to help diagnose Alzheimer’s, but they are expensive and invasive.
Previous studies examined the eyes of people who had died from Alzheimer’s and reported that the eyes of such patients showed signs of thinning in the center of the retina and degradation of the optic nerve.
In the current study, the researchers used a noninvasive technique called optical coherence tomography angiography to examine the retinas in eyes of 30 study participants.
The people had an average age in the mid 70s, and none of whom exhibited clinical symptoms of Alzheimer’s.
About half of those in the study had elevated levels of the Alzheimer’s proteins amyloid or tau as revealed by PET scans or cerebrospinal fluid.
This suggests that although they didn’t have symptoms, they likely would develop Alzheimer’s.
In the other people, PET scans and cerebrospinal fluid analyses were normal.
The eye test used in the study shines light into the eye, allowing a doctor to measure retinal thickness, as well as the thickness of fibers in the optic nerve.
A form of that test often is available in ophthalmologist’s offices.
The team also added a new component to the more common test: angiography, which allows doctors to distinguish red blood cells from other tissue in the retina.
Of the patients studied, 17 had abnormal PET scans and/or lumbar punctures, and all of them also had retinal thinning and significant areas without blood vessels in the centers of their retinas.
The retinas appeared normal in the patients whose PET scans and lumbar punctures were within the typical range.
This means in the patients with elevated levels of amyloid or tau, there were significant thinning in the center of the retina.
The researchers suggest that everyone has a small area devoid of blood vessels in the center of our retinas that is responsible for the most precise vision.
But this zone lacking blood vessels was much bigger in people with preclinical Alzheimer’s disease.
This eye exam 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.
The team hopes to use this technique to understand who is accumulating abnormal proteins in the brain that may lead them to develop Alzheimer’s.
The study’s first author, Bliss E. O’Bryhim, MD, Ph.D. is a resident physician in the Department of Ophthalmology & Visual Sciences.
Their study is published in the journal JAMA Ophthalmology.
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Source: JAMA Ophthalmology.
