Early detection of dementia may be closer than we think, and it might not come from conventional neurological tests, but rather from the eyes. A new study reveals that subtle changes in the retina can be an indicator of dementia up to 12 years before the onset of clear symptoms.
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These findings open new possibilities for early diagnosis, which could help improve care and treatment for those at risk of the disease. So, how can the eyes reveal the health of the brain?
Our eyes can reveal a lot about the health of our brain. In fact, eye problems may be one of the first signs of cognitive decline.
A recent study showed that a decline in visual sensitivity could predict dementia up to 12 years before its diagnosis.
The study followed over 8,600 people in England for several years.
By the end of the study, 537 participants had developed dementia, allowing the team to observe factors that might have preceded the diagnosis.
At the beginning of the study, participants were asked to perform a visual sensitivity test. In this test, they had to press a button as soon as they saw a triangle forming within a field of moving dots.
Those who were later diagnosed with dementia were much slower at recognizing the triangle on the screen compared to those who remained unaffected by dementia.
Why Does This Happen?
Visual problems may serve as an early indicator of cognitive decline, as the toxic plaques associated with Alzheimer’s disease may first affect brain regions linked to vision. As the disease progresses, parts of the brain associated with memory also become damaged.
Thus, vision tests may reveal deficits before memory tests do.
Several aspects of visual processing are affected in Alzheimer's, such as the ability to detect lines (contrast sensitivity) and the ability to distinguish certain colors (the ability to see the blue-green spectrum is often affected in the early stages of dementia).
This can impact people's lives without them being immediately aware.
Another early sign of Alzheimer’s disease is difficulty with "inhibitory control" of eye movements, where distracting stimuli seem to capture attention more easily.
People with Alzheimer's appear to have trouble ignoring distracting stimuli, causing issues in controlling eye movements.
Face Recognition
The study also found evidence suggesting that people with dementia tend to process new faces ineffectively. In other words, they do not follow the usual pattern of scanning the face of the person they are talking to.
In healthy individuals, this process moves from the eyes to the nose and then to the mouth. We do this to "stamp" the face and remember it later.
In fact, some doctors who work with people with dementia can often recognize the condition by simply meeting a person.
People with dementia may sometimes appear lost because they do not deliberately move their eyes to scan their environment, including the faces of people they’ve just met.
It makes sense that this early issue with recognizing people could be related to inefficient eye movement when encountering new faces, rather than being purely a memory disorder.
Can Eye Movement Improve Memory?
Since visual sensitivity is linked to memory performance (even when non-visual tests are used), the team tested whether encouraging people to move their eyes more would help improve memory.
Previous research in this area has been mixed, but some studies have found that eye movement can enhance memory.
This might explain why people who watch more television or read more tend to have better memory and are less likely to develop dementia compared to those who do not engage in these activities.
When watching television or reading, our eyes move back and forth across pages of a book or a television screen.
However, people who read a lot also tend to have spent more time in education.
Having a good education provides brain reserve, so that when connections in the brain become damaged, the negative impact is less.
In other studies, it was found that rapid eye movements from left to right and right to left (two movements per second) can improve autobiographical memory.
Despite these exciting discoveries, using eye movements to treat memory problems in older adults has not been widely implemented yet.
Additionally, the lack of regular use of eye movement deficits as a diagnostic tool is due to the possibilities offered by eye-tracking technology.
One obstacle may be the availability of eye-tracking devices, which are expensive and require training to use and analyze.
Until more affordable and user-friendly eye-tracking devices become available, eye movements cannot be used as a diagnostic tool for early-stage Alzheimer’s disease outside of the laboratory.
