Originally published April 1, 2023 on Prevention.com

Alzheimer’s disease and related dementias impact about 5.8 million people in the U.S., but properly diagnosing the condition is tricky. Now, a new study finds that early symptoms of Alzheimer’s may actually show up in the eyes.

The study, which was published in the journal Acta Neuropathologica, analyzed donated tissue from the retina (the light-sensitive layers of nerve tissue at the back of the eye) and brains of 86 people with different degrees of mental decline—the largest study on retinal samples and dementia conducted so far, according to the researchers. This tissue was then compared to tissue from donors who had normal cognitive function.

The researchers found there were increases in beta-amyloid, a hallmark of Alzheimer’s disease, in the tissue of people who had either Alzheimer’s disease or early cognitive decline. Researchers also discovered that microglial cells, which repair and maintain other cells and clear beta-amyloid from the brain and retina, declined by about 80% in people who had cognitive issues.

The researchers concluded that the findings “may lead to reliable retinal biomarkers for noninvasive retinal screening and monitoring of Alzheimer’s disease.”

The study raises a lot of questions about a possible eye test for Alzheimer’s disease—whether it may be coming and why looking at the eyes may help diagnose the condition. Here’s the deal, according to doctors.