Eye scan may detect Alzheimer's disease early

Scientists have developed a new non-invasive eye scan that can identify Alzheimer's long before the onset of symptoms, an advance that may help develop preventative strategies for the neurodegenerative disease.
The test uses polarised light to highlight deposits called amyloid proteins found at the back of patients' retinas decades before they experience cognitive decline. "The ability to detect amyloid deposits in the retina prior to disease symptoms may be an essential tool for the development of preventative strategies for Alzheimer's and other dementias," said Melanie Campbell, professor at University of Waterloo in Canada.

In order to diagnose Alzheimer's disease and other forms of dementia, doctors currently rely on either a combination of late-stage symptoms and expensive positron emission tomography (PET) brain scans or tests on the brain after death. The new method would give a less expensive, more available alternative to PET. The research established the diagnostic method's proof of concept in both human and an animal model.

Campbell showed that polarised light scans are as sensitive as other more established methods and can be done cost-effectively without using irritating dyes, making it potentially useful as an in-office screening tool.
"Amyloid proteins are made up of protein fibres with different refractive indices along and across the fibres," said Campbell. "They light up the same way as when scotch tape is placed between two polarising filters. While other researchers thought that a dye was needed to make the protein visible, we were able to achieve the same results using optics and additional computer processing," she said. 

Amyloid beta protein deposits in the brain have been proven to be present in patients decades before they experience symptoms of the disease. Although the reasons this protein appears are still being debated, the fact that it also deposits in the retina, an extension of the brain, means these deposits can be used as a biomarker for diagnosing Alzheimer's disease long before symptoms appear. "Early diagnosis is important, especially since treatment options are more limited later in the disease," said Campbell.

"Widely available, inexpensive, early detection of amyloid would help researchers develop more effective treatments before the onset of symptoms," she said.