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A new study reveals the link between vision loss and dementia, pointing out that loss of visual sensitivity can predict the onset of dementia up to 12 years before it is officially diagnosed. The study is based on a long-term follow-up survey of 8,623 healthy adults in Norfolk, England, and ultimately found that 537 participants developed dementia, providing important clues for finding early signs of dementia.

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At the start of the study, participants took a visual acuity test that required them to quickly press a button when they saw a triangle formed in a moving array of dots. Results showed that those who were later diagnosed with dementia were significantly slower at identifying the triangle than those who remained free of dementia.

The reason visual problems may be an early indicator of cognitive decline is that the toxic amyloid plaques associated with Alzheimer's disease may first affect areas of the brain associated with vision. As the disease progresses, these plaques gradually affect parts of the brain associated with memory. Therefore, vision tests may reveal deficits before memory tests.

Several other aspects of visual processing are affected in Alzheimer's disease, such as the ability to see outlines of objects (contrast sensitivity) and the ability to distinguish certain colors (the ability to see the blue-green spectrum is affected early in dementia), and these effects may not be immediately noticeable.

Another early sign of Alzheimer's disease is a deficit in "inhibitory control" of eye movements, where distracting stimuli seem to attract attention more easily. People with Alzheimer's disease appear to have problems ignoring distracting stimuli, which may manifest as problems with eye movement control. These problems may increase the risk of driving accidents, which is part of ongoing research.

People with dementia tend to be inefficient at processing new faces, meaning they don't follow the usual scanning pattern (from eyes to nose to mouth) to imprint a face. This can lead to difficulty recognizing someone they've just met, not just because of memory problems, but also because of inefficient eye movements to new faces.

Because visual sensitivity is associated with memory performance, researchers are also testing whether increasing eye movements can improve memory. Previous research has had mixed results, but some studies have found that eye movements can improve memory. This may explain why people who watch more TV and read more have better memories and a lower risk of dementia.

Despite these findings, using conscious eye movements to treat memory problems in older adults is not yet widely used. Also, using eye movement deficits as a diagnostic tool is uncommon, in part because eye-tracking technology is expensive and requires specialized training to use and analyze.

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This study reveals the importance of vision loss as an early warning sign of dementia. As technology improves, the cost of eye tracking technology may decrease in the future, making it easier to use in clinical practice, thereby helping to diagnose dementia earlier and implement intervention measures.