Often called "the window to the soul," the eyes may also offer clues about something less poetic but just as important: the health of the brain.
A new study of tens of thousands of patients revealed that cheap, simple and common photographs of the retina at the back of the eye can accurately predict many of the most common risk factors that are associated with developing Alzheimer's disease.
"We know that Alzheimer's disease develops over decades, but most of the diagnostic tools focus on late stage pathology when it is too late to intervene," said Ruogu Fang , Ph.D., a professor of biomedical engineering at the University of Florida who led the new study. "By looking at novel biomarkers, like retinal health, we offer new opportunities to identify patients at risk, offer appropriate tests and encourage them to develop healthy lifestyles to mitigate their risk."
Fang and her collaborators, including UF's Adam Woods, Ph.D., and Meta researcher Yunchao Yang, Ph.D., published their findings June 16 in the Journal of Alzheimer's Disease. The work was supported in part by the National Science Foundation.
Many patients routinely have pictures of their eyes taken. Those with diabetes, glaucoma or cataracts will have many retinal photographs taken over the years. Even regular eye exams for prescription glasses can capture photos. That near-ubiquity makes analyzing retinal photographs simple and low-cost compared to other, more expensive technologies like MRIs.
By using machine learning to analyze these retinal photographs from more than 40,000 patients in a United Kingdom-based patient databank, Fang's group was able to identify regions of the retina associated with Alzheimer's risk factors, such as the arteries and optical nerve.
"With the assistance of AI, we are now able to identify subtle retinal variations that were formerly overlooked across thousands of subjects, which may function as reliable indicators of future disease risk," said Seowung Leem, a doctoral student at UF and first author of the publication.
The AI model accurately predicted biological characteristics like sex or blood pressure as well as lifestyle factors associated with developing Alzheimer's, such as smoking, alcohol use and even insomnia. While many of these factors are captured in patients' medical charts, those records are often incomplete. Some, like alcohol and smoking, rely on unreliable self-reports.
So retinal photographs may provide another, more objective way to detect these risk factors. Plus, the retinal images can capture damage accumulated over the years, which will vary between patients who share similar risk factors.
"Retinal morphology could provide measurable indicators of neurovascular integrity, which is highly relevant to Alzheimer's disease vulnerability," said Fang, who is also affiliated with the McKnight Brain Institute . "In this sense, retinal imaging functions less as a surrogate questionnaire and more as an integrated biological sensor of cumulative risk."
Fang's group has already established that retinal photographs can detect active cases of Alzheimer's disease . But scientists now believe the disease progresses over many years, even decades. So identifying early risk factors could better identify patients who could respond to earlier interventions — including protective lifestyle changes, some medications or even brain training — before irreversible damage to the brain takes place.
