A future non-invasive eye test may allow early detection of Alzheimer's disease before memory loss kicks in, say a team led by an Indian-origin researcher.

Retina being an extension of the brain, the optical coherence tomography angiography (OCTA) will check patients' vision as well as brain health, said the study published in the journal Ophthalmology Retina. The researchers said that loss of blood vessels in retina would reflect changes in the brain, be it for both healthy people or Alzheimer's patients.

"We know that there are changes that occur in the brain in the small blood vessels in people with Alzheimer's disease, and because the retina is an extension of the brain, we wanted to investigate whether these changes could be detected," said lead author Dilraj S. Grewal, ophthalmologist at Duke University.

Using the OCTA that uses light waves that reveal blood flow in every layer of the retina, the researches checked more than 200 people. They found that in people with healthy brains, microscopic blood vessels form a dense web at the back of the eye inside the retina -- as was seen in 133 participants in a control group.

Conversely, in the eyes of 39 people with Alzheimer's disease, that web was less dense and even sparse in places. The OCTA machines, relatively a new noninvasive technology, measures blood vessels that cannot be seen during a regular eye examination. "It's possible that these changes in blood vessel density in the retina could mirror what's going on in the tiny blood vessels in the brain, perhaps before we are able to detect any changes in cognition," added Sharon Fekrat, ophthalmologist at the Duke University in the US.