An eye test could spot Alzheimer's disease two decades before symptoms emerge, a new study claims.

Researchers in Los Angeles trialed the test on 16 patients.

Comparing their results to brain scans, the eye test was just as successful at spotting those with twice the amount of plaque build-up in their brains.

Experts say the finding is one of the biggest breakthroughs in Alzheimer's research to date, offering the first sign of a cost-effective and non-invasive test.

'The findings suggest that the retina may serve as a reliable source for Alzheimer's disease diagnosis,' said the study's senior lead author, Dr Maya Koronyo-Hamaoui, a neurosurgeon at Cedars-Sinai.

An eye test developed by researchers in Los Angeles managed to spot Alzheimer's-related plaque build-up in the brain before symptoms had fully emerged (file image)

ALZHEIMER'S: FAST FACTS WHAT IS IT? Alzheimer's disease is a progressive, degenerative disease of the brain. A build-up of abnormal proteins causes nerve cells to die. This disrupts the transmitters that carry messages, and causes the brain to shrink. WHAT HAPPENS? As brain cells die, the functions they provide are lost. That includes memory, orientation and the ability to think and reason. The progress of the disease is slow and gradual. On average, patients live five to seven years after diagnosis, but some may live for ten to 15 years. EARLY SYMPTOMS: Loss of short-term memory

Disorientation

Behavioral changes

Mood swings

Difficulties dealing with money

Difficulties making a phone call

Difficulties following a TV show LATER SYMPTOMS: Severe memory loss, forgetting close family members, familiar objects or places

Becoming anxious and frustrated over inability to make sense of the world...

...This can lead to aggressive behavior

Eventually lose ability to walk

May have problems eating and drinking

The majority will eventually need 24-hour care HOW ALZHEIMER'S DIFFERS FROM NORMAL MEMORY LOSS: With ordinary age-related forgetfulness, you will still remember details associated with the thing they've forgotten. For example, you may forget your neighbor's name in conversation, but you still know that person is your neighbor. Alzheimer's sufferers forget the entire context. Advertisement

'One of the major advantages of analyzing the retina is the repeatability, which allows us to monitor patients and potentially the progression of their disease.'

Until about a decade ago, the only way to officially diagnose someone with Alzheimer's disease was to analyze their brain posthumously.

In recent years, physicians have been able to use positron emission tomography (PET) scans of the brains of living people, to identify markers of the disease.

However, the technology is expensive, and the test is invasive, since the patient needs to be injected with radioactive tracers.

Dr Koronyo-Hamaoui's team set out to identify a more cost-effective and less invasive technique.

The Cedars-Sinai research team collaborated with investigators at NeuroVision Imaging, Commonwealth Scientific and Industrial Research Organisation, University of Southern California, and UCLA to translate their noninvasive eye screening approach to humans.

For the study, the researchers conducted a clinical trial on 16 AD patients who drank a solution that includes curcumin, a natural component of the spice turmeric.

The curcumin causes amyloid plaque in the retina to "light up" and be detected by the scan.

The patients were then compared to a group of younger, cognitively healthy individuals.

The researchers found their results were as accurate as those found via standard invasive methods.

Yosef Koronyo, a research associate in the Department of Neurosurgery, said another key finding from the new study was the discovery of amyloid plaques in previously overlooked peripheral regions of the retina.

He said the plaque amount in the retina correlated with plaque amount in specific areas of the brain.

'Now we know exactly where to look to find the signs of Alzheimer's disease as early as possible,' said Koronyo.

Dr Keith L. Black, chair of Cedars-Sinai's Department of Neurosurgery who co-led the study, said the findings offer hope for early detection.

'Our hope is that eventually the investigational eye scan will be used as a screening device to detect the disease early enough to intervene and change the course of the disorder with medications and lifestyle changes,' said Dr Black.

The findings have been celebrated worldwide.

Dr David Reynolds, chief scientific officer of Alzheimer's Research UK, said: 'Being able to detect changes in amyloid using cost effective and readily available methods would be a promising development in the search for new ways to understand its role in Alzheimer's and identify those at risk of the disease.

'This study adds to existing evidence pointing to the possibility of detecting this feature of Alzheimer's in the retina, by using equipment that already helps ophthalmologists diagnose problems like glaucoma or macular degeneration.

'Research into retinal scans for detecting Alzheimer's is promising but still in the very early stages.

'This research only involved a very small number of people, and it didn't show whether these retinal changes could be detectable before people develop symptoms.

'It is too soon to tell whether this test will one day be useful for diagnosis of dementia but this is an active area of research.

'Alzheimer's Research UK is funding a project to investigate whether retinal scans could provide early indications of Alzheimer's disease in people with Down's syndrome, and we need to see more findings from studies like this before drawing any firmer conclusions.'