As popular thought goes, the eyes are a window to the soul; but according to researchers, they are also a reflection of a person’s cognitive health.
“The eye is a window to the brain,” says Dr. Christine Greer, ophthalmologist and director of medical education at the Institute for Neurodegenerative Diseases in Boca Raton, Florida.
“You can see the nervous system directly by looking at the back of the eye, towards the optic nerve and the retina,” she then explains.
Research is currently trying to explore how the eye can help diagnose Alzheimer’s disease before the onset of symptoms, since the disease is already well advanced when memory and behavior are affected.
“Alzheimer’s disease begins to develop in the brain decades before the first symptoms of memory loss appear,” says Dr. Richard Isaacson, a neurologist specializing in the prevention of Alzheimer’s disease and a member of the Institute of neurodegenerative.”
“If doctors are able to identify the disease in its early stages, then patients will be able to choose a healthy lifestyle and control their ‘modifiable risk factors, such as high blood pressure, high cholesterol and diabetes’ , added Dr. Isaacson.
A recent study published in the magazine Acta Neuropathologica sought to find out from which ocular signs it is possible to detect cognitive decline.
She examined tissue taken from the retina and certain of 86 people with varying degrees of mental decline.
“Our study is the first to provide in-depth analyzes of the protein profiles and molecular, cellular and structural effects of Alzheimer’s disease in the human retina and to show how they correlate with changes in the brain and cognitive functions,” said said lead author Maya Koronyo-Hamaoui, professor of neurosurgery and biomedical sciences at Cedars-Sinai in Los Angeles, in a statement.
“These changes in the retina correlate with changes in parts of the brain called the entorhinal and temporal cortices, a center for memory, navigation and time perception,” Koronyo-Hamaoui said.
Study researchers collected retinal and brain tissue samples over a 14-year period from the 86 human donors with Alzheimer’s disease and mild cognitive impairment.
The researchers then compared samples from donors with normal cognitive function to those with mild cognitive impairment and those with more advanced Alzheimer’s disease.
The study, published in February in the journal Acta Neuropathologica, found a significant increase in beta-amyloid, a key marker of Alzheimer’s disease, in people with both Alzheimer’s disease and early cognitive decline.
According to the study, microglial cells decreased by 80% in people with cognitive impairment. These cells are responsible for repairing and maintaining other cells, including removing beta-amyloid from the brain and retina.
“Markers of inflammation were also found, which might be an equally important marker of disease progression,” said Isaacson, who was not involved in the study.
“Findings also appeared in people with no cognitive symptoms or minimal cognitive symptoms, suggesting that these new eye tests may be well placed to help with early diagnosis.”
Study researchers found more immune cells tightly surrounding beta-amyloid plaques as well as other cells responsible for inflammation and cell and tissue death.
Tissue atrophy and inflammation in cells in the far periphery of the retina were the most predictive of cognitive status, according to the study.
“These findings might eventually lead to the development of imaging techniques that would allow us to diagnose Alzheimer’s disease earlier and more accurately,” said Isaacson, “and monitor its progression noninvasively by looking through the eye”.
