Our research 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 we could see what factors might have preceded this 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. People who would develop dementia were much slower to see this triangle on the screen than people who would remain without dementia.
So why might that be?
Visual issues may be an early indicator of cognitive decline as the toxic amyloid plaques associated with Alzheimer’s disease may first affect areas of the brain associated with vision, with parts of the brain associated with memory becoming damaged as the disease progresses. So vision tests may find deficits before memory tests do.
There are several other aspects of visual processing that are affected in Alzheimer’s disease, such as the ability to see outlines of objects (contrast sensitivity) and to discern between certain colours (the ability to see the blue-green spectrum is affected early in dementia), and these can affect people’s lives without them being immediately aware it.
Another early sign of Alzheimer’s is a deficit in the “inhibitory control” of eye movements, where distracting stimuli seem to hold attention more readily. People with Alzheimer’s seem to have an issue ignoring distracting stimuli, which may show up as eye-movement-control issues.
If dementia makes it harder to avoid distracting stimuli, then these problems could increase the risk of driving accidents – something we are currently investigating at Loughborough University.
For the full article by Professor Eef Hogervorst, Dr Thom Wilcockson, and Ahmet Begde visit the Conversation.