New Study: Cataract Surgery Lowers the Risk of Dementia, Alzheimer’s Disease

New Study: Cataract Surgery Lowers the Risk of Dementia, Alzheimer’s Disease

December 07, 2021

Cataracts affect most older adults at risk for dementia, and new research shows that cataract surgery is linked to a lower risk of dementia.

The Adult Changes in Thought (ACT) research is a long-running observational study with more than 5,000 individuals over the age of 65 at Kaiser Permanente Washington in Seattle.

Researchers have discovered that patients who had cataract surgery had a nearly 30% lower risk of having dementia from any cause than those who did not, based on longitudinal data from over 3,000 ACT project participants. After surgery, the lower risk lasted for at least a decade.

Cataract surgery has also been linked to a reduced risk of Alzheimer's disease. The findings were published in JAMA Internal Medicine on December 6th.

The observational study controlled for a variety of potential confounders, but still yielded a robust association, according to lead researcher Dr. Cecilia S. Lee, associate professor and Klorfine Family Endowed Chair in ophthalmology at the University of Washington School of Medicine.

"This kind of evidence is as good as it gets in epidemiology," Lee said. "This is really exciting because no other medical intervention has shown such a strong association with lessening dementia risk in older individuals."

The mechanisms underlying the link between cataract surgery and a lower risk of dementia were not investigated in this study. Researchers believe that after cataract surgery, people receive higher-quality sensory input, which could help reduce dementia risk.

"These results are consistent with the notion that sensory input to the brain is important to brain health," said co-author Dr. Eric B. Larson, a principal investigator of the ACT study, and senior investigator at Kaiser Permanente Washington Health Research Institute.

Another theory, according to Lee, is that after cataract surgery, people are getting more blue light.

"Some special cells in the retina are associated with cognition and regulate sleep cycles, and these cells respond well to blue light. Cataracts specifically block blue light, and cataract surgery could reactivate those cell,” she explained.

The findings of the study make a compelling case for more research into the eye-brain relationship in dementia. Previous research conducted by Lee's team at the University of Washington has found a substantial association between various retinal diseases, such as age-related macular degeneration, and the onset of Alzheimer's disease and dementia.

Dementia is more common in people who have macular degeneration or other retinal degenerative illnesses. In the current study, people who had cataract surgery to improve their eyesight had a decreased risk of getting dementia. Understanding the relationship between the aging eye and the brain could lead to new insights and treatments for age-related dementia.

The Study

Researchers tracked participants diagnosed with a cataract or glaucoma but who did not have dementia at the time they volunteered for the study. At the time of enrollment, none of the participants had had cataract surgery.

The Cognitive Abilities Screening Instrument, which has a score range of 0-100, is used to assess participants' cognitive abilities every two years. Participants with a score of less than 85 are subjected to additional neurological tests.

There were 853 cases of dementia and 709 cases of Alzheimer's disease among the 3,038 patients who were followed for an average of 7.8 years. Cataract surgery was performed on over half of the participants (1,382 people, or 45%).

Subjects who had cataract surgery in either eye were around 30% less likely to develop any kind of dementia for at least 10 years following their operation, according to an analysis of dementia risk.

An broad number of factors, including health-related confounders, were taken into account in the analysis. Cataract surgery may appear to have a protective effect due to a healthy patient bias, in which participants who had cataract surgery were likely to be healthier and have a lower risk of dementia.

Researchers performed analyses to account for several types of potential bias, but still found strong associations when these factors were accounted for.

Researchers excluded eye surgeries in the two years prior to dementia diagnosis to rule out the possibility that people with cognitive decline prior to dementia diagnosis may have been less conscious of vision issues, and thus less likely to have undergone cataract surgery. Even when this group was eliminated, the researchers discovered that cataract surgery was related with a lower incidence of dementia.

As another control, participants were also evaluated for a possible link between another type of eye surgery (glaucoma surgery) and dementia. In this case, no association was found.

Strengths of the study

This was a community-based prospective cohort study with a total follow-up of almost 23,000 person-years. With an average of 27 visits, more than 98 percent of the ACT group was seen by eye care clinicians at least once. A panel of specialists used research criteria to make dementia diagnosis. Healthy patient bias and other potential confounders were thoroughly explored.

Limitations of the study

As with any observational study, results could be influenced by unmeasured or residual confounding factors. For cataract diagnosis, there could be coding errors. Researchers only looked at the participant's first cataract surgery, so they don't know if subsequent procedures had an impact on dementia risk. The majority of the study population was white, and it is unclear if the effect would be observed in all populations.