Early dementia could be detected with a simple eye test, similar to those used to test for high blood pressure and diabetes, US scientists believe.
The eyes can reveal warning signs of many diseases
The test, developed by a team led by Dr Lee Goldstein, of Brigham and Women's Hospital, Boston, uses a non-invasive laser to study the lens of the eye.
It checks for deposits of beta-amyloid - the protein found in the brains of those with Alzheimer's disease.
The procedure has worked in a trial in mice, a conference in Spain heard.
During the trial, a brief pulse of infrared light into the eyes of four mice with Alzheimer's and four without accurately identified which had the condition.
Dr Goldstein and his team envisage the test could be used to detect the disease at its earliest stages as well as to track disease progression and monitor how people respond to Alzheimer's treatments.
Currently there is no simple test to make a diagnosis of dementia and it can only be confirmed with certainty by looking at someone's brain in a post-mortem examination.
The scientists believe the technology, known as quasi-elastic light scattering, may detect the very earliest stages of amyloid deposits in the lens, even when they appear completely clear to the naked eye.
Early detection window
The amyloid deposits appear as unusual cataracts. These are different from common, age-related cataracts.
Dr Goldstein told the International Conference on Alzheimer's Disease and Related Disorders in Madrid: "Amyloid in the lens can be detected using extremely sensitive, non-invasive optical techniques.
"This makes the lens an ideal window for early detection and disease monitoring in Alzheimer's."
The scientists acknowledge that much more work is needed before such a test could be available to use in patients.
Professor Clive Ballard, of The Alzheimer's Society, said: "This exciting study uses a new imaging technique which has enormous potential as a relatively inexpensive and non-invasive way to chart the growth of amyloid, the protein at the core of the plaques which develop in the brain in a person with dementia.
"But we are long way from eye scans being regularly used to diagnosis someone with dementia.
"More research is needed to show exactly how the amount of protein in the eye relates to development of dementia."