An eye exam might spot people with Alzheimer's disease before they show any symptoms, researchers report.
Deterioration of optic nerve
"All of us have a small area devoid of blood vessels in the centre of our retinas that is responsible for our most precise vision. We found that this zone lacking blood vessels was significantly enlarged in people with pre-clinical Alzheimer's disease," explained co-principal investigator Dr Rajendra Apte. He is a professor of ophthalmology and visual sciences at Washington University School of Medicine in St. Louis.
The study was published in the journal JAMA Ophthalmology.
Previous studies have found that the eyes of people who had died from Alzheimer's showed signs of thinning in the centre of the retina and deterioration of the optic nerve.
In this new study, Apte's team used a non-invasive technique called optical coherence tomography angiography to examine the thickness of the retinas and fibres in the optic nerves of 30 people, average age mid-70s, who had no symptoms of Alzheimer's.
A form of the test is available at many eye doctors in the United States.
More than 2.2 million South Africans have Alzheimer’s, and many are stigmatised because of the condition. According to Alzheimer’s South Africa spokesperson Debbie Beech, “In South Africa there is still the stigma in rural areas that people with Alzheimer’s are ‘bewitched’ or are simply acting out.”
Invasive and expensive methods
After the eye tests, PET scans and cerebrospinal fluid analyses revealed that about half of the study participants had elevated levels of the Alzheimer's-related proteins amyloid or tau. So, even though they didn't have any Alzheimer's symptoms, these people were likely to develop the disease.
"In the patients with elevated levels of amyloid or tau, we detected significant thinning in the centre of the retina," Apte said in a university news release.
According to study first author Dr Bliss O'Bryhim, "This technique has great potential to become a screening tool that helps decide who should undergo more expensive and invasive testing for Alzheimer's disease prior to the appearance of clinical symptoms." O'Bryhim is a resident physician in the department of ophthalmology and visual sciences.
"Our hope is to use this technique to understand who is accumulating abnormal proteins in the brain that may lead them to develop Alzheimer's," she added.
It's believed that Alzheimer's-related plaques can accumulate in the brain two decades before symptoms appear, so scientists are trying to find ways to detect the disease earlier.
Currently, PET scans and lumbar punctures are used to help diagnose Alzheimer's, but these methods are invasive and expensive.
Further research is needed, but this eye test could one day make it possible to screen people in their 40s or 50s for early signs of Alzheimer's, and begin treatment to delay further progression of the disease, the study authors suggested.
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