Diagnosing Dementia Through the Retina

Lumis Romero/Flickr

By Jackie Rocheleau
BU News Service

Many say that the eyes are windows to the soul. Actually, they may be a window to something else — like frontotemporal dementia.

For years, researchers have been trying to find a way to diagnose dementia while the patient is still alive. They can use behavioral tests to measure symptoms, but have no way to physically see what’s going on in the brain early in the disease course.

Now they’re getting closer. The retina, a bundle of nerve cells at the back of the eye, may give scientists a way to physically diagnose dementia.

The term dementia encompasses many different conditions that attack various parts of the brain, causing deficits in memory, thinking and personality. One variant of dementia, frontotemporal dementia, preferentially targets the frontal and temporal lobes of the brain. For any type of dementia, the most difficult diagnostic task is ruling out others. For example, patients with frontotemporal dementia can resemble those with Alzheimer’s or Parkinson’s disease, making it difficult to treat the correct cause. To add to that pressure, dementias are progressive, meaning that early diagnosis is crucial to ensure patients the best quality of life.

Currently, medical professionals can only conclusively diagnose dementia by examining the brain after death. A post-mortem diagnosis does little more than provide families with some sense of closure. If doctors can diagnose dementia accurately before death, they may develop ways to improve quality of life and end of life care.

For that reason, University of Pennsylvania’s Benjamin Kim is searching for specific biomarkers in the retina that may speed up diagnosis.

Kim joined a small cohort of researchers who have already started studying a retina-dementia link. Some studies found that the inner layers of patients’ retinas weaken and thin as their conditions worsen, but why the disease affects the retina is not totally clear. Some researchers theorize that frontotemporal dementia targets a protein in the brain called tau that also exists in the retina. Tau proteins normally help provide structural support for cells. In frontotemporal dementia, that support falls apart, leaving tangles of tau littered throughout the brain.  

In his experiment, Kim used a retinal imaging technique to examine the cellular layers of his patients’ retinas. He looked at 38 patients with frontotemporal dementia and compared them to a control group of 44 people of the same age with healthy brains. He noticed that the outer layers of the dementia patients’ retinas were much thinner than those of the control group. Even after considering other variables, like age, he found that the more severe the case, the thinner the retinal layers.

Though not the first study to look for biomarkers in the context of frontotemporal dementia, Kim’s is one of the few to turn to the retina for answers.

Brad Dickerson, a neurologist who specializes in frontotemporal disorders at Massachusetts General Hospital, said that Kim’s study provides interesting data, but noted that the results are extremely preliminary and not ready for clinical application. Other researchers cited the need to replicate the results and describe clear guidelines for diagnosis via retina thickness.

This experiment also did not examine the wide variety of pathologies frontotemporal dementia can take on. This limits the extent to which Kim’s findings can be generalized to all cases.

With these caveats in mind, Kim stated, “It’s possible that certain neurodegenerative diseases may have certain retinal pathologies. If that’s the case, then that really helps develop the idea that the retina could be a useful biomarker.”

Despite the reservations, this study marks an important milestone in the search for biomarkers. Neurologists have yet to find the soul when scrutinizing their patients’ eyes, but soon, they may find something equally revealing.

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