Can you identify the early stages of Alzheimer’s disease with an eye exam? Not yet.

Current diagnostic techniques for identifying Alzheimer’s disease and other dementias — which include cognitive and functional assessments, brain imaging, and neurological exams — are typically administered once cognitive decline has already been noted. But researchers hope that one day physicians may be able to diagnose the condition years before complications arise. 

In promising news, some of the latest studies have shown a strong link between Alzheimer’s and changes in the retina of the eye, which could lead to a new, noninvasive method of identifying the disease.

A Bit of Background

A slew of studies over the last few years have attempted to understand the links between our eyes, our brains and dementia. It’s not hard to see why scientists would think a link exists; the retina is a light-sensing organ located at the back of the eye that relays visual information to the brain. It follows, then, that damage in one could likely have an impact on the other. In 2021, a study at the Mayo Clinic linked the presence of retinopathy (eye disease that affects the retina) to an increased risk of stroke, dementia and premature death. Then, in 2022 two major studies dove deeper into the connection between dementia and eye disease: One, published in Aging & Mental Health, was a meta-analysis of past research that found different types of vision impairment problems (particularly cataracts) were more likely to develop before dementia. The other study, from the British Journal of Ophthalmology looked at the link between the speed at which dementia develops and the onset of other eye conditions such as age-related macular degeneration. 

Why the New Study Is Exciting

While many of the previous studies provided strong correlations between eye disease and dementia, they did not indicate a specific, quantifiable method of measuring these correlations. In this latest NIA-funded study published in Acta Neuropathologica, however, researchers found that amyloid deposits in the retina were five times higher in people with mild cognitive impairment (MCI) and nine times higher in those with Alzheimer’s, compared to cognitively unimpaired individuals. (Amyloid deposits or plaques are formed when abnormal levels of this naturally occurring protein clump together, disrupting normal cell function. Currently, much of the research around Alzheimer’s disease involves analyzing various forms of the beta-amyloid protein.) Essentially, it showed that those with worse dementia had more amyloid deposits in their retinas. 

This is exciting because, as stated in the study’s abstract, it “identifies and maps retinopathy in MCI and AD [Alzheimer’s disease] patients, demonstrating the quantitative relationship with brain pathology and cognition, and may lead to reliable retinal biomarkers for noninvasive retinal screening and monitoring of AD.” 

A Closer Look

As this article from the National Institute on Aging explains, researchers at Cedar-Sinai Medical Center in Los Angeles analyzed donated postmortem retina and brain tissue from 86 people. In addition to measuring the levels of amyloid deposits, the research team analyzed the retina tissue for the presence of microglia and other immune cells of the nervous system. Microglia help to clear cellular debris — including amyloid deposits. The researchers found that the number of microglia was increased in MCI and Alzheimer’s retinas, but were seemingly ineffective at clearing the amyloid deposits. This suggests that these retinal microglia may not be functioning property, which also happens in the brains of people with Alzheimer’s.

The team also compared other proteins in the retinas and brain tissue from donors with Alzheimer’s against those with normal cognition. They found that in both the brains and retinas of people with AD, proteins involved in processes that cause inflammation and the breakdown of neurons were activated, while those involved in producing cellular energy and light perception were inhibited. These results seem to suggest that changes in the brain with Alzheimer’s may be mirrored in the retina. 

If further studies are able to strengthen these findings, scientists are hopeful that it may be possible to identify the early stages of Alzheimer’s disease with a simple eye exam.

Top image by peakSTOCK from Getty Images Pro, via Canva.com


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