As people live longer, the number of individuals diagnosed with dementia is steadily rising. Early detection, using a variety of tests, can bring much-needed clarity to both the person diagnosed and their family. Research shows there is a link between vision problems and the risk of dementia.
Currently there’s no single reliable marker that can sufficiently measure future dementia risk; many suggest that having such a marker would greatly improve the existing situation.
According to Alzheimer’s Disease International, up to three quarters of those with dementia worldwide have not received a diagnosis. Perhaps even more shocking is their estimate that nearly 62% of healthcare practitioners across the globe incorrectly believe that dementia is part of normal aging.
Why Tests are So Important for a Dementia Diagnosis
Currently, various standardized tests are used to reach a dementia diagnosis, including cognitive and psychiatric evaluations and assessments, brain scans, and genetic tests. For the most part, these tests are not definitive – and even more limited to the earliest stages of dementia.
Whilst there is significant research and investment in early detection blood tests for use in clinical settings, other researchers are looking into one potential but often-overlooked early detection signal: vision
In this article, we’ll look at one of the latest studies published on vision and early dementia detection by Begde and colleagues (1) and whether vision testing could potentially improve the effectiveness of early dementia detection.
The emerging link between vision problems and risk of dementia
Studies have suggested a potential association between visual impairment and the increased risk of future dementia. Vision problems and cognitive decline, as seen in dementia, could be interrelated. According to researchers in this latest study, this could be due to a number of potential factors:
1. Someone with poor vision may require greater mental effort to process visual information; this may deplete resources that the brain needs for other functions.
2. Poor vision may also result in social withdrawal and isolation, which is a known risk factor for cognitive decline.
3. Both impaired vision and cognitive decline may share the same processes within the brain, so that vision and overall brain health are affected simultaneously.
Visual deficits in people with dementia
People with dementia often experience both lower-level and higher-level visual deficits.
Lower-level visual processing refers to basic visual functions like seeing details (visual acuity), differentiating colors (color vision), and detecting contrast (contrast sensitivity).
Higher-level processing, on the other hand, involves more complex visual tasks like visual integration (combining visual information) and visuospatial function (judging spatial relationships).
Current screening tests for dementia
Dementia is primarily diagnosed by evaluating cognitive decline in areas like memory, attention, executive function, and language. Various cognitive screening tests are performed in a clinical setting, including the Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA) and Addenbrookes Cognitive Examination (ACE).
Whilst none of these tests include a dedicated vision test, some cognitive tasks do assess cognitive domains that rely to some extent on visual processing.
For example, the assessment might include tasks that indirectly assess visuospatial function. This is a component of vision that involves processing spatial relationships and visual information. These assessments may measure the ability to remember what you’ve seen or to identify and interpret visual information, as well as the capacity to understand the position and arrangement of objects in space.
Whilst there are some elements that could assist in the identification of vision problems, researchers point out that they lack comprehensiveness and do not evaluate other visual functions that may be relevant to the risk of dementia. Some of these tests would include visual skills such as processing speed, hand-eye coordination, contrast sensitivity, and visuospatial constructional abilities.
Let’s look at each of these to understand more.
Processing speed
When driving, we must quickly identify traffic signs and pedestrians, judge distances, and react to other moving vehicles. Our brains need to make sense of what our eyes see so that we can drive safely. Processing speed is about the time it takes for the brain’s visual system to process and interpret visual information.
Hand-eye coordination
Hand-eye coordination involves an interplay between visual information processing and motor skills. Think about a ball game. The player has to see a moving ball, determine its location, move their body in relation to it, and determine and execute the appropriate response (running toward it and catching it, swinging a bat to hit it, etc.).
Contrast sensitivity
We need to distinguish objects from their background. That’s easier when there is a large contrast between the two. When the difference is more subtle, it may be difficult to see the object clearly.
Think about how much easier it is to read black letters on a white background than trying to read gray text on a lighter gray background. The same principles are at work when we try to recognize faces in a crowd.
Visuospatial constructional abilities
Getting dressed, putting make-up on, pouring liquid into a glass, seeing food on a plate and using a knife and fork to eat it, navigating menus and buttons on our phones. All these things require us to plan, organize, and reproduce spatial relationships between objects or shapes.
We must see and interpret the shapes, sizes, and positions of objects; understand the relationships between objects in space including distance, orientation, and direction; and use our motor skills to manipulate the objects we see.
The current study
The aim of the current study by Begde and colleagues was to validate the Visual Sensitivity Test (VST) against two well-established dementia screening tools: the Hopkins Verbal Learning Test (HVLT) and the Short Form Extended Mental State Examination (SF-EMSE). VST was used to evaluate components such as simple and complex motor response times, visual contrast sensitivity, and complex visuospatial perception.
From previous studies, the researchers identified that a lower VST score was associated with an increased risk for dementia compared to healthy individuals. This suggested a potential association between poor VST performance and early dementia risk.
The study’s objectives included (1) determining whether the VST could identify individuals with and without dementia risk and (2) understanding whether a low VST score would independently predict the risk of dementia (after accounting for other factors such as demographics, health conditions, self-reported health, and physical activity levels).
The researchers used data from the European Prospective Investigation into Cancer Norfolk study, a population-based prospective cohort study (EPIC-Norfolk Study, 2021).
What did they find?
The results of the study were somewhat surprising. They found that the VST was not an accurate indicator of dementia risk – but neither were the HVLT nor the SF-EMSE. None of these measures were highly sensitive or specific to screening for future dementia risk in this group of participants.
The results did, however, demonstrate that slower visual processing speeds – whether in simple or complex tasks – were linked to a higher risk of developing dementia in the future. When assessed along with other risk factors for dementia (e.g., age, gender, educational status, physical activity levels, and self-reported visual problems) they found the VST to be quite good at identifying those at risk.
The authors proposed that integrating the VST with existing cognitive tests may result in more accurate assessments of cognitive impairment, allow for earlier detection, and potentially provide more precise identification of those at risk for developing dementia.
Tips for protecting your vision
If this study has shown us anything, it’s how important vision is to our brain health. So here are a few tips that can help you to protect your eyesight:
1. If you’re over 65, schedule an eye exam at least once a year.
2. Eat a balanced diet of healthy foods that includes a variety of food types to ensure a range of essential vitamins and minerals.
3. Certain chronic health conditions, including diabetes and high blood pressure, can increase your risk of vision issues. It’s essential to manage these conditions with the help of your health practitioner.
4. Wear sunglasses that block UV rays when you’re outdoors.
5. Give your eyes a rest and take breaks from computer and smartphone screens and other electronic devices.
6. Make sure you have adequate lighting for tasks like reading to avoid straining your eyes.
The importance of vision tests
When we think about dementia, we seldom think about our vision. This study shows us how vision problems and dementia risk may be interrelated, making it important to include regular vision tests in clinical risk assessments.
After all, the earlier the risk for dementia is identified and measured, the sooner we can begin interventions to help mitigate that risk.
References
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 Feb 29;14(1):5016. doi: 10.1038/s41598-024-55637-x. PMID: 38424122; PMCID: PMC10904745.
3. Alzheimer’s Disease International Dementia Facts and Figures – https://www.alzint.org/about/dementia-facts-figures/
