The key to detecting Alzheimer’s disease before it ravages the brain may be in the eyes, and a quick test could potentially serve as a screening tool in the future, researchers reported Thursday.
Using the noninvasive technique, doctors peered into the eyes of older people who had no signs of dementia and found abnormalities in the retinas of those who also had biomarkers for the disease.
The study, published in JAMA Ophthalmology, was small, so more research is needed. But the hope is an eye exam could one day measure Alzheimer’s risk in people who are decades away from showing any symptoms, said Dr. Gregory Van Stavern, co-author and professor of ophthalmology and visual sciences at Washington University School of Medicine in St. Louis.
“In the brain, the pathologic changes usually start developing at least 20 years before dementia begins,” Van Stavern told TODAY.
“We don’t start treating people until they’re demented. So by the time the dementia develops, there’s already so much loss of neurons that the horse is out of the barn.”
Currently, biomarkers — brain changes and abnormal levels of certain proteins measured by scans and spinal taps — can predict whether a person who has normal cognition now will go on to develop Alzheimer’s. But these tests are invasive, expensive and time-consuming.
The appeal of the eye test is that it could perhaps give patients and doctors similar information, but inexpensively, within minutes and without the need for needles, anesthesia or recovery time, Van Stavern said.
There’s already a large body of literature showing structural changes in the retina and the optic nerve in patients with established Alzheimer’s disease, he noted. That tells tells researchers the pathologic changes in the brain are parallel to some degree to the changes in the eye.
The study involved 30 people who showed no signs of dementia, but 14 of them were diagnosed with preclinical Alzheimer’s based on their positive biomarkers, as measured by a PET scan or cerebral spinal fluid testing, or both.
The researchers examined each person’s retina and optic nerve using optical coherence tomographic angiography (OCTA), a machine that shines light into a patient’s eye to measure retinal thickness, vascular networks and blood flow patterns.
It turned out an area in the center of the retina without any blood vessels was much larger in the participants who had the biomarkers for Alzheimer’s than those who didn’t. It was also thinner.
"It is increasingly becoming apparent that the eye provides an important window on what might be going on in the brain"
The patients themselves wouldn’t notice any vision changes because of this difference, Van Stavern said. And it couldn’t be spotted by the patient looking in the mirror or a family member looking at their eyes.
It takes an OCT machine, which most eye doctors already have in their offices to look for retinal disease like macular degeneration and glaucoma, he noted. The novel part used in the study is OCT angiography, which uses the same machine, but requires adding a different program.
There’s no dye or dilating needed, nothing touches the eye and the test takes five minutes or so, Van Stavern said.
The authors emphasized this is preliminary research. They hope to expand the study to more subjects and follow them over time. The future of Alzheimer’s is intervening when patients have changes inside their bodies, but show no symptoms, Van Stavern noted.
Brain experts called the findings intriguing and potentially exciting, but cautioned more work is needed.
“It is increasingly becoming apparent that the eye provides an important window on what might be going on in the brain,” said Masud Husain, professor of neurology at the University of Oxford, in a statement to the Science Media Centre.
“It would be premature to come to any general conclusions from these findings. Nevertheless, this is a promising avenue of research.”
A cheap, non-invasive and reliable screening test for the earliest stages of Alzheimer's disease would speed up the development and testing of treatments, Robert Howard, professor of old age psychiatry at the University College London, told the Science Media Centre.