A non-invasive eye exam, similar to those given in eye doctors’ offices, might someday help predict a person’s risk of developing Alzheimer’s disease, a new study suggests.
The study, “Association of Preclinical Alzheimer Disease With Optical Coherence Tomographic Angiography Findings,” was published in the journal JAMA Ophthalmology.
While the findings are preliminary and further studies are necessary, they suggest a less costly and invasive way to identify risk.
The build-up of amyloid plaques in the brain — the main suspect in triggering nerve cells’ death in Alzheimer’s disease — is thought to occur two decades before a person begins to develop symptoms.
To detect the disease researchers use positron emission tomography (PET) scans and lumbar punctures. During a PET scan, a person is injected with radioactive tracer molecules that bind to amyloid plaques. The PET scan is able to detect this radiation and create a detailed image of the plaques in the brain, indicating density and location.
During a lumbar puncture, clinicians use a hollow needle inserted between the bones of the lower back to collect a sample of the fluid that circulates in the brain and spinal cord, the so-called cerebrospinal fluid (CSF).
Previous studies have shown that people with Alzheimer’s have alterations in their eyes, namely thinning in the center of the retina, with reduced blood flow and narrowing of blood vessels, and degradation of the optic nerve.
Now, Washington University School of Medicine in St. Louis researchers used a non-invasive technique called optical coherence tomography angiography that allows them to visualize tiny blood vessels in the retina to see whether Alzheimer’s patients carry retinal alterations that might distinguish them from healthy controls.
They examined the retinas of 30 people participating in The Memory and Aging Project at Washington University’s Knight Alzheimer’s Disease Research Center. The participants had normal cognition, mean age of 74.5 years, and showed no symptoms of Alzheimer’s disease.
Fourteen patients were diagnosed with preclinical Alzheimer’s — they were positive for key Alzheimer’s biomarkers (amyloid or tau protein) on a PET scan or CSF test. Sixteen participants who were negative for Alzheimer’s biomarkers served as the control group.
“In the patients with elevated levels of amyloid or tau, we detected significant thinning in the center of the retina,” study author Rajendra S. Apte, MD, PhD, said in a press release.
“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,” Apte said.
All participants underwent the optical coherence tomography angiography test. During the examination, which shines light into the eye, the ophthalmologist can measure the thickness of the retina and the fibers of the optic nerve. Angiography also allows detailed examination of blood vessels in the retina using X-rays.
The results showed that all participants with preclinical Alzheimer’s had retinal thinning and a significant lack of blood vessels in the center of the retina. The control participants had normal retinas.
“The angiography component allows us to look at blood-flow patterns,” said study lead author Gregory P. Van Stavern, MD. “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 retina and central nervous system are so interconnected that changes in the brain could be reflected in cells in the retina,” Apte said.
VanStavern said, “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.”
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