Poets say the eyes are the window to the soul, but it turns out they can reveal a lot about the health of our brain, too.
According to a new study published in the journal Scientific Reports, eye health can predict dementia at least 12 years before the disease is diagnosed.
The study suggests that visual problems may be an early indicator of cognitive decline. Doctors say the earlier dementia-related diseases can be diagnosed, the better chance a person has to live a longer and higher quality life.
According to the research, harmful amyloid plaques associated with Alzheimer's disease, which disrupt cell function, may first affect areas of the brain linked to eyesight. As the disease advances, memory-related areas suffer damage, leading to more obvious cognitive decline.
"So vision tests may find deficits before memory tests do," the study authors said in a statement.
The study was based on 8,623 healthy people in Norfolk, England, who were followed up for many years. By the end of the study, 537 participants had developed dementia, so researchers could see what factors might have preceded the diagnosis.
"At the start of the study, we asked participants to take a visual sensitivity test. For the test, they had to press a button as soon as they saw a triangle forming in a field of moving dots," the authors said. "People who would develop dementia were much slower to see this triangle on the screen than people who would remain without dementia."
Aspects of visual processing that are affected in Alzheimer's disease include: the ability to see outlines of objects (contrast sensitivity); to discern between certain colors (the ability to see the blue-green spectrum is affected early in dementia); and the "inhibitory control" of eye movements, where distracting stimuli seem to hold attention more readily -- and researchers say these can affect people's lives without them being immediately aware of it.
Researchers are now trying to determine if visual sensitivity is related to memory performance, and are testing whether getting people to do more eye movements helps to improve memory.
"Despite these exciting findings, treatment for memory problems using deliberate eye movements in older people has not been done that much yet," the authors said. "Also, using deficits in eye movements as a diagnostic is not a regular feature, despite the possibilities in eye movement technology."
The strongest known risk factor for dementia is increasing age, with most cases affecting those of 65 years and older, according to the CDC.