Vision problems may indicate the development of dementia 12 years before diagnosis

Eye problems can be one of the first signs of cognitive decline. A recent study showed that a loss of visual sensitivity can predict dementia up to 12 years before it is diagnosed.

Three researchers from Loughborough University – Eef Hogervorst, Professor of Psychobiology, Ahmet Begde, PhD student in Neurorehabilitation, and Thom Wilcockson, Senior Lecturer in Psychology – explain their discovery in an article appearing in Science Alert.

The research was based on 8,623 healthy people in Norfolk, England, who were followed for a number of years. By the end of the study, 537 participants had developed a form of dementia, allowing them to analyze what factors might have preceded this diagnosis.

What do eye disorders reveal?

Visual disturbances can be an early indicator of cognitive decline because Toxic amyloid plaques associated with Alzheimer’s disease may first affect areas of the brain related to visionwhile those associated with memory are damaged as the disease progresses. Vision tests may therefore detect some deficits even before memory tests.

There are many other aspects of visual processing that are affected in Alzheimer’s disease, such as the ability to see the outlines of objects (contrast sensitivity) and to discriminate between certain colors (the ability to see the blue-green spectrum is impaired in early stages of dementia). Another early sign of Alzheimer’s is a deficit in the “inhibitory control” of eye movements, where distracting stimuli seem to attract attention more easily. People with Alzheimer’s appear to have difficulty ignoring distracting stimuli, which can manifest as problems with eye movement control. “If dementia makes it more difficult to avoid distracting stimuli, then these problems could increase the risk of driving accidents, something we are currently investigating at Loughborough University,” the scientists point out.

Face recognition

“Some evidence suggests that people with dementia tend to process new faces inaccurately. In other words, they do not follow the usual pattern of scanning the face of a person they are talking to,” explain the authors of the article. «In healthy people, this would go from the eyes to the nose, to the mouth. This is done to “imprint” the face in the memory and remember it later.”
Sometimes, however, it is possible to perceive when the person you are talking to does not do so, because he may seem “lost”, he does not intentionally move his eyes to scan the environment or the faces of the new people he has just met.

«It follows that later on we are less able to recognize people because their features have not been imprinted in our memory», the scholars point out. “This initial problem in recognizing newly encountered people may be related to ineffective eye movements to new faces, rather than representing a pure memory impairment.”

Can eye movement improve memory?

However, “because visual sensitivity is related to memory performance (even using non-visual tests), we are also testing whether getting people to make more eye movements helps improve memory. Previous research on the topic is conflicting, but some studies have found that eye movement can improve memory. Perhaps this explains why we found that people who watch more TV and read more have better memories and a lower risk of dementia than those who don’t. As we watch TV or read, our eyes slide back and forth across the page and the television screen. However, people who read frequently also tend to have a longer educational background. Having had a good education provides a brain reserve capacity such that when connections in the brain are damaged, the negative outcome is less,” they point out in the article.

In other studies, “left-to-right and right-to-left eye movements performed rapidly (two eye movements per second) have been found to improve autobiographical memory (your life story). However, some studies suggest that this beneficial effect of eye movement only benefits right-handed people. We’re not sure why.”

What can change with these results?

Despite these interesting findings, not much has yet been done to treat memory problems using intentional eye movements in older people. Furthermore, “the use of eye movement deficits as a diagnostic tool is not a regular practice, despite the possibilities offered by technology”, explain the authors. «One of the limitations could be access to eye-tracking technologies, which are expensive and require training to use and analyze. Until cheaper, easier-to-use eye trackers become available, using eye movements as a diagnostic tool for early-stage Alzheimer’s is not possible outside the laboratory».