The blood vessels in your eyes may allow for earlier detection of Alzheimer's disease, a new Duke study suggests.

Professor of Ophthalmology Sharon Fekrat was struck with a unique medical opportunity in 2017 when two 96-year-old genetically identical twins came into her office. One had advanced Alzheimer's disease, whereas the other did not. The only physical difference between the two was their eyes.

“The eye is actually a direct extension of the brain," Fekrat said. "The retina is like the wallpaper of the inside of the eyeball—it’s nerve tissue. It shares many features with the brain and central nervous system."

The brain and eye also share biomarkers that can be used in diagnosing Alzheimer's, such as levels of the protein amyloid-beta. Spinal fluid is also found in the vitreous gel within the pupil, Fekrat explained, and levels of amyloid-beta in these fluids can correlate with lower cognitive test scores.

The research involved a collaboration with the Duke Neurological Disorders Clinic, where the team gathered participants with varying mental states. 

“Our study is the largest prospectively imaged group in current literature,” Fekrat said.

The control group consisted of 254 eyes from 133 people categorized as being “normal" and cognitively healthy. There was an intermediate group of 72 eyes from 37 people with minor cognitive impairment (MCI). Finally, the study collected scans of 70 eyes from 39 patients with Alzheimer's, as diagnosed by the neurology clinic using many mental state tests.

In both the control group and the MCI group, scans showed that microscopic blood vessels in one cell layer of the retina were considerably thicker than those in patients with Alzheimer's. 

These results were interesting in two ways, Fekrat explained.

First, there was no difference between the density of blood vessels in the eyes of cognitively healthy and MCI groups, although MCI has long been thought to be a precursor to Alzheimer's. Fekrat said that the researchers later plan to separate those MCI patients who are diagnosed as having amnesia and those who aren’t to see if the forgetfulness is tied to Alzheimer's.

A long-term goal of the study is to include repeat imaging over the course of time to see how retinal structures change as people age, but this goal is reliant on the amount of funding that the team can secure.

Ultimately, Fekrat explained that retinal scans may allow for early detection of Alzheimer’s, letting patients to enter clinical trials before it is too late for the potential drugs to be effective. This type of detection could also be used for other neurological degeneration diseases such as multiple sclerosis and Parkinson’s disease. The study found Alzheimer's to be statistically significant even after testing for potential significance of factors other than the disease, such as age, sex and years of education. 

Fekrat also noted that, because the study excluded 22% of their original participants for better data, the research team might need to test more people. For example, they excluded scans of patients that had existing conditions that could show similar findings, such as diabetes or glaucoma. 

There will be a continuation of tests in August that will study such parameters, as well as include patients with diabetes and glaucoma. Additionally, the researchers want to learn more about the connection between MCI patients and Alzheimer's. 

“Looking forward, we need to image many more patients," Fekrat said. "These people were just from North Carolina, and the majority were Caucasian. We need to study more diverse populations. We need to validate our data in larger populations."