Alzheimer's disease could be detected in patients up to 20 years before symptoms appear with a simple eye test, researchers say.

Trials by US and Australian researchers have found changes in the eye's retina may mirror changes that occur in the brain with dementia.

Retinal specialist at Duke University Medical Centre Eleonora Lad said people with early-stage Alzheimer's disease experienced abnormalities in vision, perception of colour, motion and peripheral vision.

Dr Lad and her colleagues have developed novel image-analysis software that is able to make correlations between eye layer thickness and other structural changes to determine how likely someone is to develop Alzheimer's disease 10 to 20 years before symptoms appear.

"It is becoming more evident that if we can treat dementia early, before symptoms occur and too much damage is caused, the progress of the condition can be stalled," Dr Lad said.

"It is possible that in the future, an image could be analysed on the spot and any suspicious images would be referred to that person's GP for further consultation."

Medical researcher at Macquarie University Mojtaba Golzan is undertaking a similar experiment that suggests changes in small blood vessels in the eye reflect the development of Alzheimer's disease.

Dr Golzan said the research might lead to a low-cost and non-invasive test for dementia.

Alzheimer's Australia chief executive Carol Bennett said it was becoming evident that the way Alzheimer's disease and other types of dementia were detected and diagnosed could become much simpler and quicker in the next decade.

Dr Lad and Dr Golzan will present their research at the Alzheimer's Disease International conference in Perth on Thursday.