Toronto researchers are testing a technique they say has the potential to be a painless, easy and economical way of identifying the growing number of individuals affected by the neurodegenerative disease – one that consists of a simple eye exam.
Using a specialized camera and software that analyzes how light reflects off the back of a person’s eye, they believe they may be able to detect patterns specific to Alzheimer’s disease even before symptoms develop, including signs of the presence of amyloid, a toxic protein characteristic of the disease.
“Changes in the brain are also visible in the back of the eye,” said Sharon Cohen, behavioural neurologist and director of the Toronto Memory Program, which is testing the retinal scan. “The cells in the brain are mirrored in the back of the eye. The blood vessels in the back of the eye are also similar in characteristics to what’s going on in the brain.”
If the retinal scan proves to be as accurate as a PET (positron emission tomography) scan or spinal tap, currently the best tools available for diagnosing Alzheimer’s disease, Dr. Cohen said people may one day be able to learn whether they have early signs of the disease during a routine eye exam.
The search for a quick, cheap and easy-to-administer Alzheimer’s test comes at a time when roughly half a million Canadians are diagnosed with the disease or other forms of dementia, and an estimated 78,600 new cases of dementia are diagnosed each year. This number does not include the many who are undiagnosed and who may not yet exhibit symptoms.
“We have an urgent need to diagnose more accurately, and early,” Dr. Cohen said.
While biomarkers, or tell-tale signs, of Alzheimer’s disease can be detected in spinal fluid collected through spinal taps or on PET scans even before symptoms develop, they are not ideal for testing the large numbers of people expected to be affected by the disease, Dr. Cohen said. Spinal taps are invasive, they are typically performed at specialty clinics, and the spinal fluid must be sent away for analysis. PET scans, meanwhile, are expensive, requiring an injection of radioactive tracers, she said.
The retinal scan, developed by RetiSpec, a medical imaging company that received funding from the Ontario Brain Institute and the Centre for Aging and Brain Health Innovation, consists of a special “hyperspectral” camera that mounts atop a standard machine used by optometrists and opthamologists for retinal examinations. Unlike a regular camera that captures the colours red, green and blue, the hyperspectral camera can capture tens or even hundreds of colours.
The company then uses artificial intelligence to analyze the image taken by the hyperspectral camera, and picks up patterns in the colours reflected at the back of the eye to determine whether the individual has signs of Alzheimer’s. It generates results within minutes.
The Toronto Memory Program plans to test the technology on at least 100 volunteers within the next few months. Volunteers will be individuals who are at risk of developing Alzheimer’s disease or have early symptoms. The results of their retinal scans will be compared with the results of their PET scans and spinal taps to test the validity of the RetiSpec tool.
If successful, the company intends to move toward commercializing the technology in Canada, RetiSpec chief executive and co-founder Eliav Shaked said.
He envisions it could be used anywhere that Alzheimer’s disease screening currently takes place, such as memory clinics, as well as by optometrists and opthamologists as part of annual eye exams.
Considering the eye as a window into the brain is something Chris Hudson has been doing for years. Dr. Hudson, a professor in the school of optometry and vision science at the University of Waterloo, is leading a multiyear study to investigate how changes in the retina may reflect changes in the brains of those affected by Alzheimer’s, Parkinson’s and other neurological disorders.
While the RetiSpec technology detects changes in the reflection of light, Dr. Hudson and his team are focusing on changes in the structure of the retina, using a type of imaging called optical coherence tomography. They have scanned the retinas of about 600 Ontarians with known neurological conditions and are continuing to track them every six months to a year.
“We’ve not had an amazing breakthrough at this point,” Dr. Hudson said. “This kind of research is very labour-intensive and it has to be done methodically and carefully.”
Dr. Hudson said his lab has previously used technology similar to RetiSpec’s for measuring oximetry, or oxygen levels, in the blood vessels of the eye. He said he is optimistic that hyperspectral imaging may one day be used to diagnose diabetic retinopathy, or diabetes-related damage to the eyes. But he anticipated that using it to identify Alzheimer’s disease may be much more challenging, because of the likely signal-to-noise ratio involved in detecting amyloid.
“I just think it’s potentially going to be a very difficult thing to quantify,” he said.
If RetiSpec’s technology is proved valid, those identified as having early signs of Alzheimer’s must still face the fact there are few treatments for the disease, and no cure. Dr. Cohen said there is nevertheless a need to give people accurate diagnoses to help them cope, strategize and access services, and to prepare for the day when more effective treatments do become available.
“It’s better to put a label on it and get help,” she said. “In our experience, people don’t do very well without information.”
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