Researchers are finding strong evidence that cataract surgery is associated with a lower risk of developing dementia.
The Adult Changes in Thought (ACT) study is an observational study that has been going on in Seattle for more than a decade. The longitudinal data of over 3000 participants in the ACT study shows that subjects who had surgery for cataracts had a 30% lower risk of developing dementia. The risk was lowered for at least a decade after surgery. Cataract surgery was associated with a lower risk of Alzheimer disease dementia. The results were reported in December.
The observational study adjusted for a number of potential confounders, but still yielded a strong association.
Lee said that the evidence is as good as it gets in epidemiology. "This is really exciting because no other medical intervention has shown such a strong association with decreasing dementia risk in older individuals."
The mechanisms by which dementia risk is reduced is not determined in this study. Researchers theorize that people may be getting higher quality sensory input, which may have a beneficial effect in reducing the risk of dementia.
The results are consistent with the idea that sensory input to the brain is important to brain health.
Lee said there is a possibility that people are getting more blue light.
Cataracts block blue light and could reactivate some special cells in the retina, which are associated with cognitive and sleep disorders.
The results of the study show a strong case for further research on the eye-brain connection. The link between Alzheimer disease and dementia has been shown in previous studies by Lee's group at the University of Washington. The current study shows that subjects who have vision-improving cataracts have a lower risk of developing dementia. Understanding the connection between the aging eye and the brain can offer insights and potential therapies to slow or prevent age-related dementia.
The study tracked participants who had been diagnosed with a disease but who did not have dementia at the time they volunteered. The participants did not have surgery for cataracts at the time. Every two years, participants are evaluated for their cognitive abilities based on the Cognitive Abilities Screening Instrument, which scores in a range from 0-100. People with scores less than 85 are subjected to neurological tests.
The Alzheimer's disease was diagnosed in 709 subjects during the follow-up of 3,038 participants. Roughly half of the participants had surgery. The analysis showed that subjects who had had their eyes closed were less likely to develop dementia after 10 years after their surgery.
An extensive list of factors was adjusted for the analysis. Cataract surgery may have a protective effect due to a healthy patient bias, where participants who underwent the surgery might have been healthier and at lower dementia risk. The researchers found strong associations when they accounted for potential bias.
Researchers excluded eye surgeries in the two years prior to dementia diagnosis to rule out the possibility that people with cognitive decline may have been less conscious of vision issues. The researchers found a lower risk of dementia with this group excluded.
The participants were evaluated for a possible link between eye surgery and dementia. No association was found in this case.
This was a prospective cohort study with more than 23,000 person-years of follow up. 98% of the cohort were seen by eye care clinicians at least once. A panel of experts made dementia diagnoses. The possibility of patient bias and potential confounders were thoroughly investigated.
The results of the study could be explained by unmeasured or residual factors. There could be coding errors. Only the first surgery was evaluated so researchers don't know if subsequent surgeries affect dementia risk. It is not clear if the effect would be seen in all populations, as the majority of the study population was White.
The Alzheimer's Drug Discovery Foundation (ADDF), a nonprofit dedicated solely to accelerate the discovery, said that innovative research like Dr. Lee's is helping to uncover how age-related changes in our senses contribute to dementia.
The ADDF is supporting Dr. Lee's work to develop new diagnostic tools for Alzheimer's that use artificial intelligence and non-invasive eye scans.
The study was funded by the Alzheimer's Drug Discovery Foundation.
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