Cataracts affect the majority of elderly people who are at risk of dementia, and new research shows that having cataract surgery reduces one’s risk of getting the disease.
An observational study of more than 3,000 ACT study participants over the age of 65 at Kaiser Permanente Washington in Seattle found that people who had cataract surgery had a 30% decreased risk of developing dementia, compared to those who did not.
After surgery, the lower risk lasted for at least a decade. Cataract surgery was also linked to a reduced risk of Alzheimer’s disease dementia.
The findings were published today in JAMA Internal Medicine.
“This kind of evidence is as good as it gets in epidemiology,” said Lead researcher Dr. Cecilia S Lee.
“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 incidence of dementia were not investigated in this study. According to the researchers, after cataract surgery, patients may receive higher-quality sensory input, which may help to reduce the incidence of dementia.
“These results are consistent with the notion that sensory input to the brain is important to brain health,” Dr. Eric B. Larson, co-author of the study added.
Another theory, according to Lee, is that following cataract surgery, people are exposed to 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,” she added, “Cataracts specifically block blue light, and cataract surgery could reactivate those cells.”
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 found a substantial association between various retinal illnesses, 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.
Researchers followed up on people who had been diagnosed with a cataract or glaucoma but didn’t have dementia at the time they participated in the study. At the time of participation, 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 testing.
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 percent). The study showed that 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.
An broad number of covariates, including health-related confounders, were taken into account in the analysis. Cataract surgery could 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 conducted analyses to account for a variety of potential biases, but even when these factors were taken into account, robust relationships remained.
To rule out the idea that patients with cognitive impairment prior to dementia diagnosis were less aware of vision issues and hence less likely to have undergone cataract surgery, researchers eliminated eye procedures in the two years prior to dementia diagnosis. Even when this group was eliminated, the researchers discovered that cataract surgery was related with a lower incidence of dementia.
Participants were also tested for a possible link between another form of eye surgery (glaucoma surgery) and dementia as a secondary control. There was no link discovered in this case.
As with any observational study, results could be influenced by unmeasured or residual confounding factors. For cataract diagnosis, there could be coding problems.
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 bulk of the participants in the study were White, so it’s uncertain whether the effect would be seen in all populations.
Source: 10.1001/jamainternmed.2021.6990
Image Credit: Getty
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