By Emma Suttie, D. Ac AP
Our eyes and ears are windows into the brain, and changes in vision and hearing can be some of the earliest indicators of cognitive decline—potentially pointing to more-serious problems.
Recent studies have uncovered links between vision changes and hearing loss in patients with Alzheimer’s disease and other dementias, helping researchers to understand the connections between these senses and changes in the brain. The findings could lead to screening techniques that could predict the onset of dementia in high-risk populations much sooner than we can now—perhaps even early enough to prevent its onset.
Vision and Dementia
A recent study, published in Scientific Reports, found that a reduction of visual sensitivity “can predict dementia twelve years before it is diagnosed.”
Researchers from Loughborough University in the UK studied 8,623 healthy adults in Norfolk, England, following up with them for many years. By the end of the study, 537 participants had developed dementia, giving researchers insights into what may have caused the disease.
At the beginning of the study, participants did a visual sensitivity test. They looked at a screen with a field of moving dots and were asked to press a button when a triangle appeared. Those who would later develop dementia were much slower to see the triangle than those who didn’t.
The researchers set out to figure out why.
They suspect that changes in visual sensitivity may be early indicators of cognitive decline because the vision centers of the brain may be affected by the amyloid plaques associated with Alzheimer’s—and that these areas are affected first—before the parts of the brain related to memory, which only become damaged as the disease progresses. The implication is that vision tests could predict these early changes before memory tests could.
According to an article by the study’s authors, Alzheimer’s affects visual processing in other ways. For example, contrast sensitivity—the ability to see an object’s outline—and how we distinguish some colors, specifically the blue-green spectrum, are affected at the onset of dementia. These changes could be happening without the person knowing it.
The authors say that another early sign of Alzheimer’s is a loss in eye movements, or “inhibitory control.” This loss means that distracting stimuli tend to hold more of our attention, making focusing a challenge. Those with Alzheimer’s have issues with their ability to ignore these distracting stimuli, which has implications for things such as driving and the risk of accidents, which the authors say they are also investigating.
Recognizing faces is another area in which people with Alzheimer’s may struggle, with some evidence suggesting that those with dementia process seeing new faces differently and less efficiently. This difference in processing has to do with eye movement patterns that we use when we scan the face of someone we have just met. Usually, when we encounter new people, our eyes scan their faces from top to bottom—from their eyes to their noses and down to their mouths, helping us to create a sort of “imprint” so that we can more easily remember them the next time.
Doctors working with dementia patients can sometimes sense dementia in patients upon meeting them because they often seem lost and don’t scan their environment or the faces of those to whom they are speaking. This lack of information gathering would make it more difficult for them to remember where they had been and who they had been talking to, and it explains why they may not recognize the same people the next time they meet.
The authors say that this difficulty with facial recognition in early dementia could be a sign of visual changes rather than an issue related solely to memory.
Hearing and Dementia
Hearing also affects dementia development and progression. Research has shown that hearing loss doesn’t just make you more likely to develop dementia—it may be a cause of the disease.
According to a 2020 Lancet Commission report, those with hearing loss have a higher risk of developing dementia, and the report lists hearing loss as one of the most significant risk factors.
In an article on the Johns Hopkins website, Dr. Frank Lin, director of the Cochlear Center for Hearing and Public Health at the Bloomberg School, suggests a few reasons why:
1. When hearing is impaired, the brain works harder to hear, diverting resources from other areas of the brain—such as thinking and memory.
2. Hearing loss has been associated with reduced brain volume, causing the brain to shrink more rapidly.
3. Hearing loss causes many people to avoid social situations because engaging is difficult. These social interactions are vital to keeping the brain active, especially as we age.
Scientists also wondered if treating hearing loss with hearing aids could reduce the risk of developing the disease.
Johns Hopkins Bloomberg School of Health researchers found the answer, and their study appeared in the Journal of the American Medical Association (JAMA) in 2023.
The study analyzed 2,413 people from the National Health and Aging Trend Study, using a nationwide sample of people older than 65 who receive Medicaid—about half of whom are older than 80.
Researchers found a clear association between severe hearing loss and dementia, finding that dementia was 61 percent more prevalent in people with moderate to severe hearing loss than in those with normal hearing.
They found that people who used hearing aids fared better than those who didn’t. In the group of 853 individuals with moderate to severe hearing loss, those who used hearing aids had a 32 percent lower incidence of dementia.
“This study refines what we’ve observed about the link between hearing loss and dementia, and builds support for public health action to improve hearing care access,” Alison Huang, the study’s lead author said in the Johns Hopkins article. Ms. Huang holds a doctorate in mental health and is a senior research associate in the Department of Epidemiology at the Bloomberg School and the Cochlear Center for Hearing and Public Health.
A study published in JAMA Otolaryngology Head and Neck Surgery in 2024 had similar results. Researchers found a significant association between hearing loss and dementia in a cohort that included 573,088 people. The study states that those with hearing loss who were not using hearing aids were at a significantly higher risk of the disease than those in the same group who used hearing aids.
The study authors say their results suggest that hearing loss was associated with an increased risk of dementia, particularly among those not using hearing aids. The results suggest hearing aids “might prevent or delay the onset and progression of dementia.” The authors also note that the risk estimates in their study were lower than those in previous studies, highlighting a need for further research.
Final Thoughts
Alzheimer’s affects approximately 6.9 million Americans (and 55 million people worldwide.) With worldwide cases estimated to balloon to 78 million by 2030, insights from research on the role that vision and hearing changes play in the future development of Alzheimer’s and other dementias may pave the way for screening that could predict these diseases years before they develop—and perhaps someday, help us to avoid them altogether.
