Better get your eyes checked! How is visual sensitivity linked to dementia development?

Searching for a reliable marker

Dementia is characterised by memory and cognitive impairments that negatively impact daily activities. For decades, scientists have sought measurable markers that could reliably predict the future onset of this condition.

Although imaging techniques, psychiatric and genetic evaluations, and some blood biomarkers can refine the diagnosis, dementia remains primarily a clinical challenge. Currently, a battery of questionnaires is used to objectively assess cognitive functions.

Vision impairment and future dementia

In the early stages of dementia, a decline in the ability to process visual stimuli is often observed. Vision impairments in patients with dementia have been documented in both basic visual processes (contrast sensitivity, colour perception, simple perception, visual acuity) and higher-level processes, such as visual integration and spatial perception. Observational studies suggest a link between vision impairments and the future development of dementia.

Study on Norfolk residents

Researchers from Loughborough University decided to analyse data collected as part of a large observational study (EPIC-Norfolk – European Prospective Investigation into Cancer Norfolk study), which enrolled more than 25,000 Norfolk residents between 1993 and 1997. Participants have been regularly monitored to evaluate their health and lifestyle.

During the third follow-up, an eye examination was conducted on 8,623 healthy participants aged 48–92 years between 2004 and 2011. By the end of the analysis in 2019, 537 individuals from this cohort had developed dementia.

Visual sensitivity test

The eye examination included a test in which participants had to press a button as soon as they spotted a triangle forming in a field of moving dots. Those who later developed dementia showed significantly slower reaction times compared to other participants.

Individuals with poor performance on the simple visual processing speed test had a 39% higher risk of later developing dementia (hazard ratio [HR] 1.39; 95% confidence interval [CI] 1.12–1.67; p < 0.01). For those with low scores on the complex visual processing speed test, the estimated risk was 56% higher (HR 1.56; 95% CI 1.27–1.90; p < 0.01). Combining visual processing speed tests with other neuropsychological assessments could improve the accuracy of identifying dementia risk.

Memory problem or an eye issue?

The Loughborough University team is now exploring how the ability of the eyes to move effectively is related to memory. Some doctors working with dementia patients can identify these individuals just by looking at them. Many patients appear lost because they do not move their eyes to scan their surroundings or the faces of people they are speaking with.

Healthy individuals tend to scan a new face from the eyes to the nose and mouth. This unconscious process helps us remember the facial features of the person so we can recognise them later. If a person’s face is not scanned, it is unlikely that we will remember it.

Problems with facial recognition in patients with Alzheimer’s disease may therefore not only stem from memory issues but also from inefficient eye movements. However, before visual processing speed tests can be routinely used in diagnostics or eye movement training introduced into dementia treatment, we will need to wait for further study results.

Editorial Team, Medscope.pro

Sources:

1. Begde A., Wilcockson T., Brayne C., Hogervorst E. Visual processing speed and its association with future dementia development in a population-based prospective cohort: EPIC-Norfolk. Sci Rep 2024; 14 (1): 5016, doi: 10.1038/s41598-024-55637-x.
2. Hogervorst E., Begde A., Wilcockson T. How your vision can predict dementia 12 years before it is diagnosed – new study. The Conversation, 2024 Apr 10. Available from: https://theconversation.com/how-your-vision-can-predict-dementia-12-years-before-it-is-diagnosed-new-study-226356