The study builds on research showing that closely examining the retina might help detect Alzheimer’s in its early stages. The retina is made up of brain tissue. Retinas are connected to the brain via the optic nerve. Changes in the brain from dementia, including Alzheimer’s, can also show up in the retina.
In a small study, researchers at Washington University in St. Louis identified about 30 people with no signs of Alzheimer’s. They then tested all of these people with two ways of measuring biological changes associated with the disease. One is a PET scan of the brain. The other is an examination of spinal fluid.
A little more than half of the people tested showed no signs of Alzheimer’s in the biological tests. The others had biological signs or markers of the disease. These markers are proteins or clusters of proteins found in the brains of people with Alzheimer’s.
Next, the researchers scanned the eyes of everyone in the study. They used a scan called optical coherence tomographic angiography (OCTA), which creates a detailed cross-section of the retina. OCTA scanning can map blood vessels in the retina.
They found changes in the retinas of the people who also had biological signs of Alzheimer’s. The people without Alzheimer’s markers had normal retinas.
The biological tests for Alzheimer’s, looking at spinal fluid or a brain PET scan, are complicated, expensive, and pose risks for patients. They are rarely used to diagnose the condition.
Most Alzheimer’s is diagnosed through memory tests or observing behavior changes. By the time changes in behavior are noticed, the disease can be advanced. While Alzheimer’s has no cure, medications and social programs may slow the disease. Experts are eager to find ways to diagnose Alzheimer’s early.
Ophthalmologist Sunir Garg, MD a retina specialist at Wills Eye Hospital in Philadelphia, called the Washington University study an exciting start. But he cautioned that the study is small, and much more work is needed.
“Hopefully this will stimulate a lot more research,” Garg said. “We know from previous studies that certain changes in Alzheimer’s disease have similarities to changes we see in the retina. The retina is a direct extension of the brain.”
Garg stressed that patients with abnormal OCT scans shouldn’t assume they have Alzheimer’s. “Just because you have changes in the retina doesn’t necessarily enable us to diagnose Alzheimer’s.”
The eye is one of the few parts of the body where an ophthalmologist can see blood vessels, nerves and other tissues that are usually hidden. And for some conditions, changes in the eye may be the first sign of trouble. Diabetes, high blood pressure, autoimmune diseases, sexually transmitted diseases and cancers have all been diagnosed from eye exams. And eye exams have even saved lives that would have been lost to stroke.
Research on the links between eye health and brain health is growing. There is much more to learn, Garg said.