November 13, 2013
Your Eyes May Tell The Tale Of Alzheimer’s Onset
[ Watch the Video: Vision Loss Linked With Alzheimer’s Disease ]
Susan Bowen for redOrbit.com - Your Universe OnlineIn the future, your optometrist may be the first person to realize that you could have Alzheimer’s disease (AD). An international team of researchers has discovered the loss of a particular layer of retinal cells may reveal the presence of the disease.
Led by R.C. Chang from the University of Hong Kong, along with researchers from Georgetown University Medical Center (GUMC) made the connection by studying a layer of the eye that had not previously been investigated. They will present their findings at Neuroscience 2013, the meeting of the Society for Neuroscience.
"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," explains R. Scott Turner, MD, PhD, director of the Memory Disorders Program at GUMC and a member of the team. "We know there's an association between glaucoma and Alzheimer's in that both are characterized by loss of neurons, but the mechanisms are not clear."
Glaucoma is a group of eye conditions resulting in damage to the optic nerve, and it may cause loss of vision. Usually the condition is caused by abnormally high pressure inside the eye, according to the Mayo Clinic. Turner says that researchers are increasingly seeing glaucoma as a neurodegenerative disease similar to AD.
The neuroscientists used genetically-engineered mice designed to develop Alzheimer’s for their research. In the eye, two cell layers transmit information, by way of the optic nerve, into the brain. These are the retinal ganglion layer and the inner nuclear layer. Most previous research has focused on the retinal ganglion layer. When the researchers measured the retinas of the Alzheimer’s mice, they found both layers had a significant loss of thickness. The inner nuclear layer had a 37 percent loss of neurons, and the retinal ganglion layer had a 49 percent loss when compared to healthy mice of the same age.
In humans, the structure and thickness of the retina can easily be measured using optical coherence tomography. This technology is increasingly finding its way into both research and clinical settings.
Turner states, "This study suggests another path forward in understanding the disease process and could lead to new ways to diagnose or predict Alzheimer's that could be as simple as looking into the eyes."
These findings also offer new hope for glaucoma patients who may be helped by treatments developed for Alzheimer’s, since the two conditions have parallel disease mechanisms.
Other recent research offers hope of another way to detect Alzheimer’s at an earlier stage. Researchers at Johns Hopkins gave a battery of cognitive tests to both people who showed early signs of memory loss and normal healthy older adults. While the graph of scores for healthy people displayed a symmetrical bell-shaped curve, the graphs of people with dementia shifted to a more asymmetrical curve. This asymmetry is caused by an uneven disruption of mental processes, with some subtle declines appearing before other, more obvious ones. Noting this shift could become another tool for reassuring some people they did not have Alzheimer’s, while allowing others to begin interventions earlier.