A routine eye test can detect the earliest stages of Alzheimer's disease in seconds, according to new research.

The non-invasive scan looks for changes in blood vessels in the retina. Tiny alterations in this small piece of tissue mirror those going on in the brain and are the first signs of dementia, say scientists.

The technique, which is called OCTA (optical coherence tomography angiography), could revolutionize treatment of the devastating neurological disorder because it enables early diagnosis. Physicians can now see blood vessels in the back of the eye that are smaller than the width of a human hair.

Senior author Professor Sharon Fekrat, an ophthalmologist at the Duke Eye Center in Durham, North Carolina, said: "If we can detect these blood vessel changes in the retina before any changes in cognition, that would be a game-changer."