New York, Aug 24 (IANS): Researchers, including one of Indian origin, are developing a non-invasive eye test which may one day help detect Alzheimer's disease even before the symptoms appear.

According to scientists, Alzheimer's-related plaques can build up in the brain two decades before the onset of symptoms such as memory loss and cognitive decline appear.

The non-invasive technique -- called optical coherence tomography angiography -- shines light into the eye, allowing a doctor to measure retinal thickness, as well as the thickness of fibres in the optic nerve.

The test detected evidence of Alzheimer's in older patients who had no symptoms of the disease.

"The retina and central nervous system are so interconnected that changes in the brain could be reflected in cells in the retina," said Rajendra S. Apte, Professor at Washington University in St. Louis.

"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," added lead author, Bliss E. O'Bryhim, from the varsity.

"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," O'Bryhim said.

In previous studies, the eyes of people who had died from Alzheimer's have shown signs of thinning in the centre of the retina and degradation of the optic nerve.

The study, described in the journal JAMA Ophthalmology,
added angiography -- which allows doctors to distinguish red blood cells from other tissue in the retina -- to the test.

In patients with preclinical Alzheimer's, the area at the centre of the retina without blood vessels was significantly larger, suggesting less blood flow, the researchers found.

"We found that this zone lacking blood vessels was significantly enlarged in people with preclinical Alzheimer's disease," Apte said.

If changes detected with this eye test can be used as markers for Alzheimer's risk, it may be possible one day to screen people as young as in their 40s or 50s to see whether they are at risk for the disease, they noted.