Image caption Patients with Alzheimer's show shrunken brain sizes (L) compared with healthy individuals (R)

Changes to specific cells in the retina could help diagnose and track the progression of Alzheimer's disease, scientists say.

A team found genetically engineered mice with Alzheimer's lost thickness in this layer of eye cells.

As the retina is a direct extension of the brain, they say the loss of retinal neurons could be related to the loss of brain cells in Alzheimer's.

The findings were revealed at the US Society for Neuroscience conference.

The team believes this work could one day lead to opticians being able to detect Alzheimer's in a regular eye check, if they had the right tools.

[This] could lead to new ways to diagnose or predict Alzheimer's that could be as simple as looking into the eyes Dr Scott Turner, Georgetown University Medical Center

Alterations in the same retinal cells could also help detect glaucoma - which causes blindness - and is now also viewed as a neurodegenerative disease similar to Alzheimer's, the researchers report.

Scott Turner, director of the memory disorders programme at Georgetown University Medical Center, said: "The retina is an extension of the brain so it makes sense to see if the same pathologic processes found in an Alzheimer's brain are also found in the eye."

Dr Turner and colleagues looked at the thickness of the retina in an area that had not previously been investigated. This included the inner nuclear layer and the retinal ganglion cell layer.

They found that a loss of thickness occurred only in mice with Alzheimer's. The retinal ganglion cell layer had almost halved in size and the inner nuclear layer had decreased by more than a third.

"This suggests a new path forward in understanding the disease process in humans and could lead to new ways to diagnose or predict Alzheimer's that could be as simple as looking into the eyes," said Dr Turner.

Non-invasive

Alzheimer's disease Symptoms include loss of memory, mood changes, and problems with communication and reasoning

No one single factor has been identified as a cause for Alzheimer's disease - a combination of factors, including age, genes, environment, lifestyle and general health are implicated

One of the leading theories involves the formation of clumps of a protein called beta-amyloid, which damage and kill brain cells The dementia timebomb

Treatments developed for Alzheimer's could therefore also be useful for treating glaucoma, he added.

But he also said that so far it was still speculation to say that retinal thinning may predict impending Alzheimer's disease.

"We're hoping that this translates to human patients and we suspect that retinal thinning, just like cortical thinning, happens long before anyone gets dementia," Dr Scott told BBC News.

"Human studies are needed to test this idea as a diagnostic [test]. Current leading biomarkers of Alzheimer's disease are either very costly or invasive. A retinal thickness scan - as measured by optical coherence tomography - would be both inexpensive and non-invasive."

Alzheimer's is a neurodegenerative disease and is the most common type of dementia. The cause is still unknown and there is currently no cure. It often goes undetected for years until so many cells die that symptoms become increasingly prevalent.

But treating the disease early is believed to be vital to prevent memory loss.

Laura Phipps, at Alzheimer's Research UK, said there was increasing evidence linking retinal cell loss to Alzheimer's disease, and that it was "positive to see this line of research being followed up".

"This early-stage study, which is yet to be published in full, was carried out in mice, and further research will be necessary to determine whether changes in the retina found here are also found in people with Alzheimer's.

"Diagnosing Alzheimer's with accuracy can be a difficult task, which is why it's vital to continue investing in research to improve diagnosis methods," Dr Phipps added.