The world’s population is aging rapidly and the prevalence of Alzheimer’s disease is on the rise.

For this reason, the need for efficient screening methods that can be applied to millions of people is dire.  Current diagnostic practices are either invasive or ineffective.  For instance, brain scans are costly, and spinal taps — or lumbar punctures — are invasive and potentially harmful.  Specialists currently diagnose Alzheimer’s disease using memory tests and by tracking behavioral changes. However, by the time that the symptoms appear, the disease has already progressed.

For these reasons, researchers are hard at work trying to devise newer and better diagnostic tools for Alzheimer’s. Now, researchers at Duke University in Durham, NC, say that Alzheimer’s could be diagnosed in seconds just by looking at a person’s eyes, and scientists at the Sheba Medical Center in Israel concur.  Two new studies presented at — the 122nd Annual Meeting of the American Academy of Ophthalmology (AAO 2018), held in Chicago, IL — show that Alzheimer’s alters the fine blood vessels in the retina at the back of the eye.  Using an innovative and noninvasive eye imaging technique, the scientists maintain that they can distinguish between signs of Alzheimer’s and signs of mild cognitive impairment (MCI), which is a condition that raises the risk of Alzheimer’s but is not harmful in itself.

The signs of Alzheimer’s disease in the retina

Using a technique called optical coherence tomography angiography (OCTA) researchers examined the link between the eyes’ retinas and Alzheimer’s disease.  Researchers used OCTA to study how dementia affects the retina because it enables them to examine the finest veins and red blood cells that are present at the back of the eye. 

In the first study, scientists compared the retinas of people with Alzheimer’s with those of people who had only MCI, and with the retinas of those who had neither of these conditions.  The researchers found that people with Alzheimer’s had lost small blood vessels in the retina at the back of the eye.  Also, a certain layer of the retina was thinner in people with Alzheimer’s than in those with MCI or people who did not have any form of cognitive impairment.  The scientists speculate that the changes in the retina reflect the disruptions in the brain’s blood vessels that Alzheimer’s causes and believe this is a valid hypothesis, given that the optic nerve connects the brain with the retina.

Alzheimer’s, the retina, and the hippocampus

In the second study, the research team examined 400 people who were at high genetic risk of developing Alzheimer’s. The scientists compared brain scans and retina images from these people with the retinas and brains of those without a family history of Alzheimer’s.  The study findings revealed that the retina is thinner in people with a higher genetic risk of Alzheimer’s. Additionally, a part of the brain called the hippocampus was smaller in these people. Both of these dementia signs correlated with a poor score on the cognitive impairment test.

The hippocampus is a key brain area for learning and memorizing. It is among the first regions that Alzheimer’s disease affects, with studies demonstrating that dementia affects neurogenesis — that is, the formation of new neurons — in the hippocampus, and that Alzheimer’s disease reduces the size of this brain region altogether.

A brain scan can only detect Alzheimer’s when the disease is well beyond a treatable phase.  Consequently, developing screening tools like retinal scans would provide low cost, low risk test with the potential for early detection.