Dementia has a devastating impact on public health, and its prevalence is expected to increase over time. “Alzheimer’s disease and related dementias affect over 10% of adults aged 65 years and older,” says Suzann Pershing, MD, MS. “According to current estimates, 7 million adults in the United States will be affected by these diseases by 2025, and up to 16 million adults by 2050. Identifying risk factors associated with dementia offers an important opportunity for early recognition and potential interventions.”
Visual and cognitive function may be interrelated for a variety of reasons. “One possibility is that dementia and visual impairment result from common causes—brain and nerve degeneration,” explains Dr. Pershing. “It’s also possible that reduced visual input leads to lower brain stimulation. Additionally, poor vision makes the brain work harder to perform tasks, which can accelerate cognitive decline.” She adds that visual impairment may also cause social isolation. Other comorbid conditions, such as vascular damage and diabetes, may further impair vision. “It’s likely that some combination of all these factors plays a role in visual and cognitive function,” Dr. Pershing says.
A New Study
For a study published in JAMA Ophthalmology, Dr. Pershing and colleagues evaluated associations between visual impairment and risk of dementia or mild cognitive impairment. “We used data from the Women’s Health Initiative, which includes women who have been carefully monitored since a clinical trial beginning in the early 1990s,” says Dr. Pershing.
The study used carefully defined and consistent methods of checking vision and a uniquely rigorous approach to defining and identifying dementia, according to Dr. Pershing. “Instead of identifying dementia using only cognitive tests, our Women’s Health Initiative dataset relied on multiple sources of data, including cognitive tests as well as clinical evaluations, interviews of family and friends, and laboratory or imaging tests,” she says. “These were then reviewed by a committee of experts. Our study design was important because dementia falls along a spectrum, and patients may experience different functional effects.”
Highlights of Key Findings
Results of the study showed that women with baseline objective visual impairment were more likely to develop dementia than those without vision impairment. “Our study compellingly demonstrated a longitudinal association between visual impairment and later development of dementia,” says Dr. Pershing. “Women with visual impairment were 2- to almost 6-times more likely to develop dementia when compared with patients without baseline visual impairment [Table].”
The study also found that associations between vision impairment and dementia or mild cognitive impairment were greater among patients who had more severe visual impairment at baseline. “The worse the vision, the higher the risk for dementia,” Dr. Pershing says. “Our findings remained even after we accounted for other factors, including age, race/ethnicity, other medical problems (including diabetes and vascular disease), baseline cognitive test scores, hearing loss, education, physical activity, and smoking.”
Considering the Implications
The American Academy of Ophthalmology recommends that older adults receive eye exams every 1 to 2 years. “Although our study did not directly address causality, it does offer a reminder and another potential reason—dementia risk—to monitor and maintain eye health in the patients we treat,” Dr. Pershing says. “In addition to screening for early signs of eye disease and offering treatment, eye exams can also help clinicians identify changes from other diseases, such as severe diabetes or hypertension, and even some autoimmune diseases.”
Identifying potentially modifiable risk factors is essential to ensuring that patients have access to interventions and support when they are most able to benefit. “Our results suggest that having poor vision is associated with higher risk of developing dementia,” says Dr. Pershing. “Identifying at-risk patients is important, but it also begs the question of whether improving vision using various interventions—updated glasses, cataract surgery, or treatments for other eye diseases—may reduce the risk of dementia. It would also be helpful to ascertain whether interventions to improve vision might benefit patients with existing dementia. These are important areas for future research.”