Could a common eye test detect Alzheimer’s disease decades earlier?

ST. LOUIS — It may be possible sometime in the future to screen patients for Alzheimer’s disease using a non-invasive eye exam. A new study finds that technology similar to what many eye doctors already use may be able to identify signs of the condition in patients.

Researchers from Washington University School of Medicine in St. Louis say they’ve detected evidence of Alzheimer’s in older patients who had presented no symptoms of the disease using the potentially groundbreaking method.

“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,” says the study’s first author Dr. Bliss E. O’Bryhim, a resident physician in at WUSL’s Department of Ophthalmology & Visual Sciences, in a statement. “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.”

Experts estimate that Alzheimer’s-related plaque starts building up in the brain as much as two decades before the onset of symptoms. Researchers have long sought to detect the disease sooner, but physicians typically use expensive and invasive methods, such as PET scans and lumbar punctures.

Previous research revealed signs of thinning in the center of the retina and the degradation of the optic nerve of people who had died of Alzheimer’s disease. This latest work involves a noninvasive technique called optical coherence tomography angiography to examine the retinas of 30 participants with an average age in the mid-70s, who haven’t exhibited symptoms of Alzheimer’s disease.

Of the 30 patients in the study, 17 had abnormal PET scans and/or lumbar punctures. All of them had retinal thinning and large areas without blood vessels in the centers of their retinas. Patients with normal PET scans and lumbar punctures also had normal retinas.

“In the patients with elevated levels of amyloid or tau, we detected significant thinning in the center of the retina,” says co-principal investigator Dr. Rajendra S. Apte, the Paul A. Cibis Distinguished Professor of Ophthalmology and Visual Sciences. “All of us have a small area devoid of blood vessels in the center of our retinas that is responsible for our most precise vision. We found that this zone lacking blood vessels was significantly enlarged in people with preclinical Alzheimer’s disease.”

Doctors measured retinal thickness in patients, as well as the thickness of fibers in the optic nerve by shining a light into the eye, a common test used by ophthalmologists. The only difference is this test also involves an angiography so that doctors can distinguish red blood cells from other tissue.

“The angiography component allows us to look at blood-flow patterns,” explains the other co-principal investigator, Dr. Gregory P. Van Stavern, 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.”

Though more research is needed to replicate the findings, the authors believe the test could be used in patients much younger, perhaps even in their 40s. That would give doctors the ability to detect and treat the disease at a far earlier point in time.

“We know the pathology of Alzheimer’s disease starts to develop years before symptoms appear, but if we could use this eye test to notice when the pathology is beginning, it may be possible one day to start treatments sooner to delay further damage,” says Van Stavern.

The study is published in the journal JAMA Ophthalmology.

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