Your Eyes and an Alzheimer's Diagnosis Test

A study links eyes tissue with brain tissue

Your Eyes and an Alzheimer's Diagnosis Test
Photo by Alexandru Zdrobău on Unsplash

Alzheimer's disease is a degenerative neural disease caused by an abnormal build-up of proteins in the brain that kills cells and damages connections between neurons. Common symptoms include memory loss, difficulty thinking, disorientation and other kinds of cognitive decline. Symptoms can also include vision problems, especially trouble with spatial relationships and depth perception. Some patients develop trouble reading, following moving objects, or have problems with contrast.

Sometimes forgotten is that there are several kinds of dementia, though Alzheimer's is the most common. It accounts for 60 to 80 percent of all dementia. Other types include vascular dementia—which is associated with stroke—dementia with Lewy bodies and frontal lobe dementia, commonly called FTD. Parkinson's disease can also cause dementia, as does Huntington's disease. Some people get mild cognitive impairment (MCI) in older age, which may or may not get worse with time or it can be the early stage of Alzheimer’s disease.

The eyes and dementia

The relationship between brain tissue and eye tissue is an area of of intensive study by ophthalmologists and neurologists. The brain plays a critical role in taking the visual information your eye gathers and putting it together into a picture that you can understand. And the optic nerve directly connects the brain to the back of the eye.

Research shows that diseases and conditions of the brain can also affect the eyes because the optic nerve and retina are actually brain tissue that extends outside the brain case. Alzheimer's disease and dementia, which are caused by damage to brain cells, both appear to have effects on the retina.

There are not currently any eye tests that can help diagnose or understand dementia, but current research shows exciting potential. Studies show a clear relationship between brain tissue and eye tissue and point toward future areas of research.

Eyes and an Alzheimer’s disease diagnosis

Previous research has shown that Alzheimer’s can cause structural changes to the retina, most notably a thinning of the inner retinal layers, even though 0ther diseases such as glaucoma and Parkinson’s disease, however, can also cause a thinning of the retina.

A study was conducted by researchers from Duke University and published in the journal of the American Academy of Opthalmology to assess the connection between the retina and the onset of Alzheimer’s.

In the study, the team shows that the topmost layer of neurons in the retina of a mouse model of Alzheimer’s disease exhibit a change in their structural texture.

Combined with data on the changes in the thickness of this layer, the new measurement could prove to be a more easily accessible biomarker of Alzheimer’s.

The new approach can measure the roughness or texture of the nerve fiber layer of the inner retina.

While it is an extremely useful imaging technique commonly used to make a wide array of diagnoses, it has limitations.

To gather more data, the team added a measurement called angle-resolved low-coherence interferometry (a/LCI), which uses the angles of the scattered light to gather more information about the tissue’s structure. By combining the two measurements, the researchers can extract both thickness and structural information about each layer of the retina.

The team says the a/LCI measurements complement the thickness measurements to improve the potential utility of more quantitative biomarkers for Alzheimer’s.

Right now, Alzheimer's disease is diagnosed after a series of assessments and exams that rule out other things. These might include cognitive testing for memory and thinking, talking to family members, physical exams and brain imaging scans.

But none of these tests actually diagnose Alzheimer's and the disease can currently only be confirmed after death by examining brain tissue. The tests may help narrow down the type of dementia or rule out other conditions with similar symptoms.

The difficulty of diagnosing Alzheimer's disease and other dementias is driving research on the eye-brain connection.

The researchers are now working to incorporate this added ability into a low-cost system that can eventually be an affordable and accurate testing system for Alzheimer’s.

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Frank Racioppi
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