The eyes are the only part of the nervous system that we can see directly, without invasive tools or expensive imaging. And this makes them like windows into the brain. Scientists are learning that vision tests and simple retinal scans can reveal important data about brain health — data that could be key to the early detection, and even the prevention, of dementia. 

Identifying cataracts or other conditions that cause vision loss could be the first step toward prevention, experts say: A recent study by the Lancet Commission linked untreated vision loss — which affects one in eight people over 50 — to a 47-percent increased risk of developing dementia. (To put that percentage in perspective, about 200 out of 10,000 older adults without vision problems will develop dementia compared to 249 with untreated vision loss.) 

The link between vision loss and dementia

As we age, visits to the eye doctor become routine. These check-ups may be the first opportunity to identify vision loss… and this can be a sign of other problems with the brain.

Social and intellectual withdrawal: The most common cause of vision loss is cataracts, a build-up of proteins in the eye’s lens which causes vision to become more blurry and clouded. It can make it more challenging to participate in social engagements or to read books, and these two activities (social interaction and building up cognitive reserve) have both been linked to lower dementia risk. 

Vascular issues: In a routine vision check-up, optometrists will also look for glaucoma, a condition caused by fluid build-up in the eye. This is yet another dementia red flag: High blood pressure, which can lead to this kind of build-up, is also a significant risk factor for dementia.

Diabetes: A close look at the eye’s blood vessels can also reveal signs of diabetes. High blood sugar leads to the outgrowth of abnormal blood vessels, leading to a condition called diabetic retinopathy, which also causes more eye damage. After spotting these signs, the eye doctor may refer you to an endocrinologist who can treat diabetes and reduce the risk of developing dementia. A class of diabetes drugs called GLP-1 agonists may also prove effective for treating symptoms — Novo Nordisk is testing the active ingredient in Ozempic and Wegovy in Phase 3 trials. 

Cognitive decline: Vision loss itself can also be a symptom of dementia. One might experience vision problems when there’s nothing wrong with the eye. Instead, the problems may lie with the brain’s visual processing centers. Visual symptoms precede memory or thinking problems in dementia.

For example, in posterior cortical atrophy, a subtype of early-onset Alzheimer’s, the first symptoms include blurred vision, visual hallucinations, and difficulty reading. An eye doctor can refer their patients to a neurologist who can check if they have PCA and get them diagnosed sooner. An early diagnosis allows people to participate in clinical trials, try approved Alzheimer’s treatments, and plan for the future. 

New eye tests to screen for dementia

All these links are opening the door to better ways to diagnose dementia. The earliest signs of Alzheimer’s — the build-up of protein plaques — might be visible in the eye 20 to 30 years before the onset of any cognitive symptoms. Scientists are developing tests that could spot these signs and could one day help eye doctors routinely screen patients for the risk of Alzheimer’s.

For example, Maya Koronyo-Hamaoui, a professor at Cedars-Sinai Medical Center, is one of the scientists helping to develop retinal scan tests that could quickly spot the earliest signs of the disease. “The retina is the only central nervous system organ not shielded bone that can be imaged directly and repeatedly,” Koronyo-Hamaoui told Being Patient.

Some of these so-far-experimental tests use AI to analyze images of the eye for signs of dementia, while others are simple eye drops that could help visualize beta-amyloid plaques. Though the timeline for these new diagnostics is hard to predict, they could one day make it easier to spot who is at high risk of developing dementia.