Eye Tests May Help Diagnose Alzheimer’s Disease

A piece of the brain that is still growing forms the back of the eye. The central nervous system is a piece of the retina. As evidence builds that changes in the brain can manifest in this region, scientists are turning to retinas as a potential screening target for early signs of Alzheimer's.

Brain autopsies were the only way to diagnose Alzheimer's. Research has made it possible to identify signs of the disease years before symptoms appear. Alzheimer's can be diagnosed at its earliest stages with the help of brain scans and tests ofCSF.

The ability to detect early disease has been improved. Diagnostic methods are expensive and can be very intrusive. The procedure of injecting a radioactive tracer molecule into the bloodstream requires a needle to be placed between the back of the neck. The right high-risk individuals should be funneled into the diagnostic process with low-cost screening tools that are easy to use. He says that the retina is an attractive target because it is related to brain tissue and can be looked at through the eye.

One approach to screening for Alzheimer's disease is to look for signs of theamyloid in the brain. Studies show that this fragment accumulates in the eye, and there is evidence that it can be seen before symptoms start.

Robert Vince and Swati More of the University of Minnesota's Center for Drug Design first described how to use a method called hyperspectral imagery, which captures an image at many different light wavelength, to identify amyloid aggregates in mouse retinas. They were able to confirm the clumps in the animals' brains. The two scientists and their colleagues found that amyloid aggregate may be an early marker in human eyes.

The technique has been licensed by the team to a Canadian company called RetiSpec, which uses machine-learning to find amyloid clumps. Clinical trials are being conducted to examine the technique's effectiveness.

More than 100 participants who were at risk of or had mild cognitive impairment were included in the trials. The technique correctly identified people with brain amyloid 86 percent of the time and correctly ruled out those without it 80 percent of the time. Sharon Cohen is the medical director at the Toronto Memory Program. Cohen says more data is needed before this can be used for diagnostic purposes. I think that will happen.

Some researchers have found amyloid plaques in the retinas of people who have no signs of cognitive decline. Robert Rissman and his colleagues at the University of California, San Diego are studying participants in a trial of an Alzheimer's drug. In a small feasibility study of eight participants, the investigators measured amyloid in the eye, and they are now screening more patients for it. Rissman says that the data may show how amyloid changes over time.

Other signs of early Alzheimer's are being studied by scientists. Researchers reported in a study published earlier this year that there was a correlation between the thickness of the eye and cognitive performance. Preliminary work shows that there is a correlation between amyloid build up in the brain and progressive changes in the retina. Changes in blood vessels are one of the retina-based markers that are being looked for by Snyder and his colleagues.

Rissman says that they are unproved at this stage. He cautions that there are a number of questions that need to be answered. The method of identifying the substance in the retinas is still being debated by scientists, and the findings from the studies of these clumps have varied from facility to facility.

Cohen says that there is enough evidence of amyloid deposition in the retina to make it certain that the finding should no longer be in dispute.

The Alzheimer's Association says that early detection and accurate diagnosis are key to getting people on the right care and treatment path. She says, "it's a really interesting time in this space, even though the full potential of the technology hasn't been determined."