A recent study found that up to 19% of dementia cases may be attributable to impaired vision. The study, published in JAMA Ophthalmology, showed that vision loss may have even more of an impact on the risk of dementia than previously thought. Scientists also consider hearing loss a modifiable risk factor for dementia. This supports the notion that sensory engagement is critical for brain health.
Different types of vision loss have different dementia risk profiles
The National Health and Aging Trends Study evaluated more than 2,700 individuals over age 65. After gathering several vision and cognitive measures on each person, the researchers calculated population attributable fractions (PAFs). A PAF is the proportion of disease cases in a population that can be attributed to a specific risk factor. The PAF of prevalent dementia from at least one type of vision impairment was 19%, reported lead author Jason Smith, ScM from Johns Hopkins University Bloomberg School of Public Health.
Rather than only measuring near vision, the researchers also tested distance vision and contrast sensitivity. Contrast sensitivity measures the ability to distinguish between subtle differences in brightness or contrast. A lower score may mean someone is less able to see in low-light conditions or distinguish between shades of gray.
The study reported that contrast sensitivity impairment had the highest PAF (15%) compared to near vision (9.7%) and distance vision (4.9%) impairments. This is higher than in some previous studies. It illustrates the importance of considering different types of vision loss related to dementia.
A focus on sensory loss
The Lancet Commission on dementia prevention, intervention, and care determined that almost half of all global dementia cases could be preventable by addressing 14 specific risk factors. Hearing loss is at the top of the modifiable risk factors. In the 2024 report, the Commission added two new factors: high LDL (low-density lipoprotein cholesterol) and vision loss.
Sensory changes have proven to be important to understanding dementia rates. An invited editorial in JAMA Ophthalmology by Drs. He and Shang of Hong Kong Polytechnic University noted that studies in the past few years have found a positive association between vision loss and the risk of dementia. “This highlights the importance of vision impairment as a potentially modifiable factor for dementia, especially considering that 80% of vision impairment cases are preventable or treatable,” the authors concluded.
What you can do to prevent dementia related to vision loss
Some of the simplest measures to reduce the risk of development of dementia are getting routine vision and hearing tests. Many of us have vision loss when viewing things up close or at a distance (near- or farsighted). We can often correct these conditions with glasses or contact lenses. It is also important to be tested for contrast sensitivity. Visual impairments that affect contrast sensitivity such as glaucoma, cataracts, or macular degeneration are more common in older adults. Be sure to talk to your eye doctor about any vision changes you’ve noticed. For other modifiable risk factors for dementia and Alzheimer’s disease, see our web pages on Alzheimer’s Disease Prevention.
