Cataracts affect most older people at risk of dementia, and now 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 a long-term observational study in Seattle at Kaiser Permanente Washington with more than 5,000 participants over 65 years of age. Based on longitudinal data from over 3,000 ACT study participants, researchers have now found that patients who had cataract surgery had an almost 30% lower risk of developing dementia from any cause than those who did not. This reduced risk persisted for at least a decade after surgery. Cataract surgery was also associated with a lower risk specifically for dementia from Alzheimer’s disease. The results were published in JAMA Internal Medicine on December 6th.
The lead researcher Dr. Cecilia S. Lee, Associate Professor and Klorfine Family Endowed Chair in Ophthalmology at the University of Washington School of Medicine, said the observational study was cleared for a number of potential confounders but still found a strong association.
That kind of evidence is as good as it gets in epidemiology. This is really exciting because no other medical procedure has shown such a strong association with reducing the risk of dementia in the elderly. “
Dr. Cecilia S. Lee, Associate Professor and Klorfine Family Endowed Chair in Ophthalmology at the University of Washington School of Medicine
The mechanisms associated with cataract surgery and a reduced risk of dementia were not determined in this study. Researchers suspect that after cataract surgery, people may receive higher sensory quality, which could have a positive effect on reducing the risk of dementia.
“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, lead researcher on the ACT study and lead researcher at Kaiser Permanente Washington Health Research Institute.
Lee said another hypothesis is that people get more blue light after cataract surgery.
“Some special cells in the retina are related to sensation and regulate the sleep cycle, and these cells respond well to blue light,” she said. “Cataracts specifically block blue light, and cataract surgery could reactivate these cells.”
The results of the study underscore a strong case for further research into the brain-eye connection in dementia. Previous studies by Lee’s group at UW have shown a strong link between other retinal diseases, such as age-related macular degeneration, and the development of Alzheimer’s and dementia. Patients with macular degeneration or other degenerative retinal diseases are more likely to develop dementia. In the current study, patients who underwent cataract surgery to improve their vision had a lower risk of developing dementia. A further understanding of the relationship between the aging eye and the brain can provide insights and potential therapies to slow or prevent age-related dementia.
The study: The researchers tracked participants who were diagnosed with cataract or glaucoma but who did not have dementia at the time they volunteered for the study. Participants also had no cataract surgery at the time of enrollment. Participants are assessed every two years for their cognitive abilities based on the Cognitive Abilities Screening Instrument, which ranges from 0-100 points. Participants with scores below 85 will have additional neurological tests.
During the follow-up of 3,038 participants (mean 7.8 years per person), 853 subjects developed dementia, including 709 cases of Alzheimer’s. About half of the participants (1,382 people, or 45%) had cataract surgery. Analysis of the risk of developing dementia showed that people who had cataract surgery on both eyes were about 30% less likely to develop any form of dementia for at least 10 years after their surgery.
The analysis has been adjusted for an extensive list of factors, including health-related confounders. Cataract surgery could have a protective effect due to a healthy patient bias, in which participants who had cataract surgery may be healthier and have a lower risk of dementia. The researchers conducted analysis to account for different types of potential biases, but still found strong associations when these factors were taken into account.
Researchers excluded eye surgery in the two years leading up to a diagnosis of dementia to rule out the possibility that people with cognitive decline prior to being diagnosed with dementia were less aware of their vision problems and were therefore less likely to have had cataract surgery. Even when that group was excluded, the researchers found a lower risk of dementia-related cataract surgery.
As a further control, the participants were also examined for a possible connection between another type of eye operation (glaucoma operation) and dementia. In this case, no connection was found.
Strengths of the degree: This was a community-based, prospective cohort study with more than 23,000 person-years of follow-up. More than 98% of the ACT cohort were seen at least once by ophthalmologists, with an average of 27 encounters. The dementia diagnoses were made by a panel of experts based on research criteria. The possibility of bias in healthy patients and potential confounders have been carefully examined.
Study restrictions: The results could be explained by unmeasured or residual confounders, as with any observational study. Coding errors can occur in cataract diagnostics. Only the participant’s first cataract operation was evaluated, so the researchers do not know whether subsequent operations have influenced the risk of dementia. The majority of the study population was white and it is unclear whether the effect would be seen in all populations.
“Innovative research like Dr. Lee’s is helping to uncover how age-related changes in our senses contribute to dementia,” said Dr. Howard Fillit, founding director and chief science officer of Alzheimer’s Drug Discovery Foundation (ADDF), a nonprofit, worked solely to accelerate the discovery and development of drugs to treat and prevent Alzheimer’s disease and related dementias.
As part of its Diagnostics Accelerator research initiative, the ADDF also supports the work of Dr. Lee to develop new diagnostic tools for Alzheimer’s disease that use non-invasive retinal imaging and artificial intelligence.
University of Washington Faculty of Medicine
Lee, CS, et al. (2021) Relationship Between Cataract Extraction and Development of Dementia. JAMA internal medicine. doi.org/10.1001/jamainternmed.2021.6990.