More than 5 million Americans 65 years and older have been diagnosed with some form of dementia, yet we still do not definitively know what causes it, most likely because there are a variety of factors at work.

Research has shown that there could be a connection between hearing loss and the onset of dementia. And now a new study reports that roughly one in five cases of dementia could be related to vision impairment in seniors who are 71 or older.

As the senses become less sharp, the brain has to work harder to sense the external environment. At the same time, the brain is undergoing its own process of aging.

Researchers at Johns Hopkins Bloomberg School of Public Health, the University of Michigan and the Duke University School of Medicine hypothesized that sensory deprivation — from a loss of hearing or diminishing vision — contributes to dementia. As the senses lose their sharpness, the brain has to work harder to sense the external environment. At the same time, the brain is undergoing its own process of aging.

The team gathered data on nearly 2,800 people in the U.S. over the age of 71 who were alive in 2021 and looked for evidence of vision loss or mental decline in each.

People in the study were given cognitive exams and tested for three types of visual impairment: their ability to see objects that were close by or near acuity; their ability to see small details in the distance or distance acuity; and their contrast sensitivity, the ability to perceive sharp and clear outlines of very small objects.

Vision loss was present in just under 20 percent of the dementia cases seen among the participants.

The team noted that:

  • About 5 percent of dementia cases were connected to vision impairment related to distance acuity
  • Nearly 10 percent of dementia cases were connected to vision impairment related to near acuity
  • 15 percent of dementia cases were connected to vision impairment related to contrast sensitivity

“The results suggest that nearly 1 in 5 prevalent dementia cases in community-dwelling U.S. adults ages 71 years or older could have at maximum been avoided if vision impairment had been eliminated.”

The results were slightly higher among participants who were from the ages of 71 to 79, as well as for women and non-Hispanic white people. This latter finding is in line with past research showing women are nearly twice as likely to be affected by Alzheimer's disease as men, primarily because women tend to live longer.

“The results from the cross-sectional study suggests that nearly 1 in 5 prevalent dementia cases in community-dwelling U.S. adults ages 71 years or older could have at maximum been avoided if vision impairment had been eliminated,” the researchers said, in a press release. “Overall, these data support the inclusion of sensory impairments as potentially modifiable risk factors for dementia prevention strategies.”

The researchers note that their findings do not prove vision loss causes dementia, but they do point out that the “total contribution of late-life-vision impairment to dementia may be substantial,” which suggests that their study warrants further research.

Eye exams are important for everyone, but especially for seniors. The American Optometric Association recommends annual eye examinations for everyone over the age of 60. And if you notice any changes in your vision you should see an ophthalmologist right away.

The study is published in JAMA Ophthalmology.