The retina as a window into Parkinson’s

Novel Cholinergic Biomarker in Parkinson's Disease: An Imaging Study of the Brain and the Eye

M Amin Banihashemi
PhD student
University of Toronto
Graduate Student Award
$20,000 over 2 years

Just as the eyes are the window to the soul, neuroscientist Amin Banihashemi hopes the retina will prove to be a window into the state of the brain in Parkinson’s disease.

The retina consists of a thin layer of nerves that line the back of the eye, sense light, and relay signals to the brain.

The brain, in turn, helps us think, store, and retrieve memories, set goals, and carry out tasks.

One of the signalling chemicals that helps regulate these brain activities is called acetylcholine. A region of the brain called the cholinergic system produces acetylcholine, and this region shrinks as Parkinson’s disease progresses. That shrinkage results in dementia.

Banihashemi, a PhD student at the University of Toronto, is measuring the thickness of the retina to see what it reveals about the volume of the brain, particularly the cholinergic region.

“What we want to do is image the eye and then estimate what’s happening in the brain.”

Like brain cells, the retina also produces acetylcholine. As Parkinson’s progresses, toxic misshapen proteins, such as alpha synuclein, accumulate in both the retina and the brain and both change in size. Just as the cholinergic region shrinks, the retina thins.

Given these similarities, Banihashemi believes the retina can be used as a mirror – or a proxy – for the brain in Parkinson’s disease.

“What we want to do is image the eye and then estimate what’s happening in the brain,” he says.

Banihashemi believes identifying shrinkage early can help pinpoint people who might be at risk of dementia. That could enable them to benefit from any potential new therapies.

Banihashemi will compare retinal scans with data from MRI scans of the brains of people with Parkinson’s who are participating in the Ontario Neurodegenerative Disease Initiative. He hopes the statistical analysis he develops will allow him to estimate brain shrinkage from the thickness of the retina.

Scanning the eye is a rapid, non-invasive, and inexpensive imaging method, making this a potentially important and accessible screening tool.

Banihashemi hopes the screening tool he studies
will also help doctors predict whether people’s memories are impaired and how well they can complete tasks.

A research career was a “natural fit” for Banihashemi, who enjoys being able to study a problem, consider the most helpful solution, and then develop it.

Banihashemi got to know families and friends of people with Parkinson’s disease when he volunteered at a Parkinson SuperWalk in 2016-2017. His conversations with them and his background in medicine inspired him to work on Parkinson’s disease.

“To get this kind of award from somewhere you’ve volunteered, where you’ve gotten to know people – it’s very sweet,” he says.

How your support made this research project possible

Research into screening tools for early identification of people with Parkinson’s and other neurodegenerative diseases leading to dementia is important because new treatments and therapies under active investigation may be more effective early in the disease, Banihashemi says.

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