July 18, 2011 (Paris) -- A simple eye test may aid in the early detection of Alzheimer's disease even before memory loss and other symptoms develop, preliminary research suggests.
The experimental test, which looks for changes in the eye that can precede the development of Alzheimer's, has only been evaluated in a small number of people. And even if the early encouraging results hold up, the test "is not perfect" on its own, says study leader Shaun Frost, MSc, a PhD candidate at the Commonwealth Scientific and Industrial Research Organization in Perth, Australia.
But used in conjunction with blood tests that spot changes associated with the development of Alzheimer's disease, "this noninvasive and cost-effective [eye] test holds promise as an early detection tool for the disease," he tells WebMD.
The findings were presented at the Alzheimer's Association International Conference 2011.
About 5.4 million Americans have Alzheimer's disease, the most common form of dementia.
Imaging scans using positron emission tomography (PET) and magnetic resonance imaging can often detect brain changes indicative of Alzheimer's years before memory and other symptoms of the disorder are evident, but they are costly and impractical for use on a population-wide basis.
Tissues of the retina -- the light-sensitive layer at the back of the eye -- are close in position to those of the brain, Frost says. "They're very closely related to brain tissue and much easier to access," he says.
In the pilot study, Frost and colleagues examined retinal photographs from 13 people with Alzheimer's disease, 13 people with mild cognitive impairment, and 110 healthy people taking part in a larger study on aging. Participants also underwent PET scans to measure the amount of Alzheimer's-associated plaque in the brain.
The researchers used the same cameras that eye doctors use to check patients' eyes, fitted with special software to measure the width and other characteristics of blood vessels in the retina.
"The hardware is out there, and the software is likely to be inexpensive," Frost says.
Eye Changes, Brain Plaque, Alzheimer's Linked
Results showed that the widths of certain blood vessels were substantially different in people with Alzheimer's than in the other participants and that the difference correlated with the amount of plaque seen on the scans.
"There is a close relationship between Alzheimer's disease, changes in the retina, and plaque burden in the brain," Frost says.
This isn't the only eye test in development for Alzheimer's. Harvard researchers have developed a pair of optical tests that look for amyloid-beta, a protein that comprises Alzheimer's plaque, in the eye lens. Other researchers are also looking at molecular changes in the eye that might predict the development of the disease.
One question is whether people will want to know whether they are at risk for a disease for which there is no effective treatment.