Clinical Context

Loss of vision and hearing can have profound results in terms of other neurological function as well as social function. These effects may raise the risk for incident dementia, and a previous retrospective study of more than 114,000 older adults with hearing loss assessed how the use of hearing aids might affect the risks for dementia, depression or anxiety, and injurious falls. The results of this study by Mahmoudi and colleagues was published in the November 2019 issue of the Journal of the American Geriatrics Society.^[1]

A total of 12.3% of all adults with hearing loss used hearing aids. Women and Black/Latinx adults were less likely to wear hearing aids. On adjusted analyses, the hazard ratios for dementia, depression or anxiety, and injurious falls associated with wearing hearing aids vs not wearing hearing aids were 0.82 (95% confidence interval [CI], 0.76-0.89), 0.89 (95% CI, 0.86-0.93), and 0.87 (95% CI, 0.80-0.95), respectively.

The current study analyzes the effect of cataract extraction on the subsequent risk for dementia while accounting for potential confounding variables.

Study Synopsis and Perspective

Older patients who undergo cataract surgery may reduce their risk of developing dementia by roughly 30%, new research shows.

Although previous studies have linked sensory impairment to dementia, whether correcting vision problems in particular can prevent cognitive decline has been unclear, according to Cecilia S. Lee, MD, the Klorfine Family Associate Professor in the Department of Ophthalmology at the University of Washington, Seattle, who led the study.

"Despite controlling for an extensive number of health-related factors and potential sources of bias that might have affected the relationship between cataract surgery and dementia, we still found strong associations between cataract surgery and reduced risk of dementia," said Dr Lee, whose group published their findings in JAMA Internal Medicine.^[2] "Cataract surgery was associated with an approximately 30 percent lower risk of developing dementia, and we found similar associations with Alzheimer disease as well."

For the analysis, Dr Lee and colleagues used data from the ongoing Adult Changes in Thought (ACT) study, a longitudinal analysis of more than 5000 people aged 65 years and older in the Seattle area who did not have dementia on enrollment. They included 3038 participants in ACT who had been diagnosed with cataracts or glaucoma before the onset of dementia. Of those, 1800 (59%) were women, 1238 (41%) were men, and nearly all (91%) were White. The mean age at cataract diagnosis was 74.4 years.

Among the study participants, 853 were diagnosed with dementia and 709 with Alzheimer's dementia. Roughly half the group (n=1382) underwent cataract extraction.

After controlling for factors linked to the risk of developing dementia, including smoking history, years of education, apolipoprotein E (APOE) genotype (which has been linked to dementia), and other factors, patients in the study who underwent cataract extraction were 29% less likely to develop dementia than those who did not undergo the procedure (hazard ratio [HR], 0.71; P<.001), Dr Lee's group found. The researchers observed similar results for the development of dementia associated with Alzheimer's dementia. However, glaucoma surgery did not appear to be linked to a reduction in the risk for dementia, they report (HR, 1.08; P=.68).

The reduction in risk was particularly strong in the first 5 years after surgery (HR, 0.68; P<.001). "When considering the relative associations of cataract extraction, additional education, White race, smoking history, sex, and APOE genotype with dementia risks, the only covariate that was more protective than cataract surgery was not having an APOE e4 allele," the authors report.

A strength of the study, Dr Lee said, was its data set, which allowed the researchers to control for many confounding variables. "Healthier patients are usually more able to go through optional surgeries than people with many medical issues. So one could argue that the reduced dementia risk that we found was from people who had cataract surgery being healthier than people who did not have cataract surgery," she said. "For this study, we had access to a unique data set that allowed us to address many confounders, such as people's health status and health behavior."

Dr Lee said the study, which was not designed to look for potential mechanisms for the association, has important implications for primary care providers.

"To date, there are only a few known dementia risk factors that are modifiable, such as certain diets and increased activity level," she said. "Our study results suggest that interventions to improve sensory impairment such as vision could play a role in preventing dementia or Alzheimer disease. Older adults who are experiencing symptoms of cataract, such as night driving difficulty or seeing halos around bright lights, should be evaluated by ophthalmologists."

Her group has also found that several neurodegenerative eye diseases, such as age-related macular degeneration and diabetic retinopathy, are linked to an increased risk for dementia, as well as Alzheimer's dementia. "Thus, primary care physicians who are taking care of older adults could play an important role in ensuring that older adults who are at risk of dementia are evaluated by ophthalmologists regularly," she said.

Michael F. Chiang, MD, director of the National Eye Institute of the National Institutes of Health, Bethesda, Maryland, which helped fund the research, said, "This study reinforces how closely the eye and the brain are linked, in this case through the association between cataract surgery and lower risk of dementia. I hope future studies will examine the underlying mechanistic relationships in more detail."

The study was funded by the National Institutes of Health, the Alzheimer's Drug Discovery Foundation, and Research to Prevent Blindness. Dr Lee has disclosed no relevant financial relationships. Several coauthors reported financial relationships with industry, a full listing of which is included in the original article.

JAMA Intern Med. Published online December 6, 2021.

Clinical Implications

• A previous study demonstrated that hearing aids were associated with lower risks for dementia, depression or anxiety, and injurious falls among older adults with hearing loss.
• In the current study, cataract extraction was associated with an approximate 30% reduction in the risk for incident dementia. This lower risk was similar in examining the relationship between cataract extraction and Alzheimer's dementia specifically. Glaucoma surgery had no significant effect on the risk for dementia.
• Implications for the healthcare team: The healthcare team may suggest that cataract extraction may improve the risk for future dementia among at-risk older adults.

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