For years, researchers have been searching for ways to identify dementia and Alzheimer’s long before memory symptoms appear. A new Chinese study points to a surprising direction: The retina in the eye may serve as a “window” into brain health – and signal future risk of dementia.
Dementia is a progressive neurological syndrome that affects memory, thinking ability, judgment, orientation, and daily functioning. Alzheimer’s is its most common type. In the Western world, one in ten people over the age of 65 is expected to develop dementia, and the number of patients is expected to double in the coming decades as the population ages.
The major problem is that once cognitive symptoms are clear, the process of brain damage is already underway and is sometimes quite advanced. Therefore, medical research is searching for early markers that can identify people at risk even before memory decline appears. This is where the retina comes into the picture.
Why the eye?
The retina is a thin layer of cells lining the back of the eyeball. It absorbs light and converts it into nerve signals that are transmitted to the brain through the optic nerve. Biologically, the retina is למעשה an extension of the central nervous system – meaning it is part of the brain, only far more accessible for examination.
Unlike the brain itself, which cannot be “seen” without expensive or invasive imaging, the retina can be examined easily, quickly, and painlessly using an OCT test – optical imaging that allows measurement of retinal layer thickness with microscopic precision.
What did the study find?
The study, published in 2025 in the scientific journal Frontiers in Aging Neuroscience, was conducted by researchers from China and analyzed data from approximately 30,000 adults over nearly a decade.
All participants underwent OCT examinations at the start of the study and were then followed medically over the years. The researchers compared retinal thickness with future development of dementia.
The results were unequivocal:
• The thinner the retina, the higher the risk of developing Alzheimer’s.
• Every measurable decrease in retinal thickness increased the risk of Alzheimer’s by about 3%.
• Participants with an especially thin retinal layer in the center of the eye had a 41% higher risk of developing frontotemporal dementia (FTD), a rarer and more aggressive type of dementia.
• Over a nine-year follow-up, 148 participants developed Alzheimer’s and 8 developed FTD.
What is the biological explanation?
The researchers believe the connection stems from the fact that the neurodegenerative processes that occur in the brain in dementia — accumulation of pathological proteins, neuroinflammation, and degeneration of nerve cells — also occur in the retina.
Since the retina is composed of nerve cells, degenerative changes in the brain may be reflected in its gradual thinning — long before a person feels changes in memory, behavior, or judgment.
In other words: The retina may serve as a “barometer” of brain health.
What is the clinical significance?
The study does not say that someone with a thin retina will necessarily develop dementia — rather, that retinal thickness can be a risk marker, similar to blood pressure or cholesterol for heart disease.
In the future, a simple OCT test at an ophthalmologist’s office may become a screening tool:
• for early identification of at-risk populations
• for monitoring the progression of degenerative processes
• and for evaluating the effectiveness of preventive treatments in the future
The major advantage is that the test is:
• non-invasive
• relatively inexpensive
• already widely available
• and does not involve radiation or injections
What is still not known?
The study found an association — but did not prove causality. It is still unclear whether retinal thinning is a result of an early brain process, or whether it is itself part of the process.
In addition, further studies are needed in more diverse populations to ensure that the findings are valid outside China and among different age and ethnic groups.
The bottom line: It is possible that the eyes truly reflect the state of the brain more than we thought. A new study suggests that retinal thickness can serve as an early window into neurodegenerative processes that lead to dementia.
We are still far from an official dementia screening test through the ophthalmologist — but this study brings us one step closer to early diagnosis, prevention, and perhaps in the future even significant delay of the disease.