The eyes serve a purpose beyond just seeing. Now, research is now indicating they tell a person’s cognitive well-being.

Recent studies have delved into the potential of using the eye as a diagnostic tool for Alzheimer’s disease before symptoms appear.

Dr. Christine Greer, director of medical education at the Institute for Neurodegenerative Diseases in Boca Raton, Florida, told Tucson that “the eye is the window into the brain,”providing a direct view into the nervous system through the optic nerve and retina.

“Alzheimer’s disease begins in the brain decades before the first symptoms of memory loss,” said Dr. Richard Isaacson, an Alzheimer’s preventive neurologist who is also at the Institute for Neurodegenerative Diseases.

Isaacson suggested that detecting the disease in its earliest stages could enable people to make positive lifestyle choices and manage their modifiable risk factors such as high blood pressure, high cholesterol, and diabetes, with the help of doctors.

How it works

A recent study investigated the extent of cognitive decline by analysing donated tissue from the retina and brains of 86 individuals with varying degrees of mental deterioration. The research sought to determine how the molecular, cellular, and structural impacts of Alzheimer’s disease in the human retina correlate with changes in the brain and cognitive function.

According to senior author Professor Maya Koronyo-Hamaoui, who teaches neurosurgery and biomedical sciences at Cedars-Sinai in Los Angeles, the study provides the first in-depth analysis of protein profiles related to Alzheimer’s in the human retina.

“These changes in the retina correlated with changes in parts of the brain called the entorhinal and temporal cortices, a hub for memory, navigation, and the perception of time,” Koronyo-Hamaoui told Tucson in a statement.

According to the authors, the study collected retinal and brain tissue samples from the largest group of donors ever studied, comprising 86 individuals with Alzheimer’s disease and mild cognitive impairment over a 14-year period.

The researchers then analysed samples from donors with normal cognitive function and compared them to those with mild cognitive impairment and later-stage Alzheimer’s disease.

The study, published in the journal Acta Neuropathologica in February, discovered substantial increases in beta-amyloid, a critical indicator of Alzheimer’s disease, in individuals with both early cognitive decline and Alzheimer’s.

The study revealed that microglial cells decreased by 80% in individuals with cognitive problems. These cells are responsible for the repair and maintenance of other cells, as well as clearing beta-amyloid from the brain and retina.

“Markers of inflammation were (also) found, which may be an equally important marker for disease progression,” said Isaacson, who was not involved in the study.

“The findings were also apparent in people with no or minimal cognitive symptoms, which suggests these new eye tests may be well-positioned to aid in early diagnosis.”

The researchers conducting the study discovered that there were increased levels of immune cells that were closely clustered around amyloid beta plaques, as well as other cells that caused inflammation and damage to cells and tissues.

According to the study, the most accurate predictor of cognitive status was the presence of tissue atrophy and inflammation in cells located in the far periphery of the retina.

“These findings may eventually lead to the development of imaging techniques that allow us to diagnose Alzheimer’s disease earlier and more accurately,” Isaacson said, “and monitor its progression noninvasively by looking through the eye.”