A quick eye exam may one day help doctors diagnose Alzheimer's disease before symptoms appear. A study by Duke Health, published March 11 in the journal Ophthalmology Retina, found that a loss of blood vessels in the retina may be an early indicator of cognitive decline.
“This is a paradigm shift. This is a completely different way to looking at a very important disease,” said Dilraj Grewal, associate professor of ophthalmology at the Duke Eye Center and a retina specialist.
A team of ophthalmologists and neurologists at Duke took pictures of the retinas of more than 200 people using a new, non-invasive technique called optical coherence tomography angiography, or OCTA. The technology can produce detailed images of blood vessels in the retina smaller than the width of a human hair, said Grewal.
"It takes between two to five minutes to acquire per eye and it gives us information about the thickness of different layers of the retina, as well as density of the blood vessels in the different layers of the retina."
Imaging of people with healthy brains showed a dense web of microscopic blood vessels inside the retina. But the retinal scans of patients who had been diagnosed with Alzheimer's disease were much different.
“We found that patients who had Alzheimer’s disease had a significantly reduced vessel density, which is the density of the capillaries (or the smallest blood vessels in the retina) as compared to folks with mild cognitive impairment and similarly aged cognitively healthy people,” said Grewal
According to the study, the differences in density were statistically significant after researchers controlled for factors including age, sex and level of education.
“There’s another metric of vascular perfusion which is called perfusion density. This was reduced in the Alzheimer’s group as well. And also there was a reduction in the thickness of some of the retinal layers, such as the ganglion cell layer and the retinal nerve fiber layer in patients with Alzheimer’s.”
These findings are similar to other studies. In 2018, researchers at Washington University in St. Louis observed signficant thinning of the retinas of patients with elevated levels of Alzheimer’s proteins amyloid or tau. Still, it's too soon to use retinal scans to diagnose patients with Alzheimer’s disease, says Sharon Fekrat, a retina specialist and professor of ophthalmology at the Duke Eye Center.
“Right now, this testing is not ready to be used in the eye doctor’s office or the neurologist’s office. Our ultimate goal is to be able to use one or more images and many different parameters or metrics from these images of the retina and optic nerve and put together what we call a diagnostic index, or a suite of biomarkers to be able to make the diagnosis of Alzheimer’s disease."
The second phase of the study will start next summer where researchers plan to follow up with some of the patients and increase the scope of their study to include other neurodegenerative diseases besides Alzheimer's. The research team at Duke is also building an online repository with thousands of retinal images that researchers all over the world can access in hopes of validating their findings and reproducing their results. If retinal scans could detect Alzheimer’s before symptoms appear, it would allow researchers to find a treatment for the disease, which does not currently exist.
"Many clinical trials have failed thus far and the reasons for that are likely very complex,” said Fekrat. “But one of those reasons could potentially be that the Alzheimer’s disease was too advanced at the time of entering into the clinical trials studying these new medications. So identifying and screening large numbers of people early to try to diagnose Alzheimer’s disease in the asymptomatic period, and then enter those patients earlier into clinical trials to study new treatments, may allow us to find an effective treatment."