How does having cataracts increase your risk of dementia?
Cataracts filter out blue-light, which is associated with cognitive function and Alzheimer’s disease. Or is it another mechanism?
I love my job and even more so when I read interesting research findings that make you sit up and think, think a bit more and potentially have major implications for health.
The study below shows that in older ‘cognitively-normal’ older people (>65 yrs) having cataract surgery reduces your future risk of developing all-cause dementia by close to a quarter. Why?
One mechanism proposed is the blue-light theory based on the fact that cataracts filter out blue light, which is associated with cognitive function and Alzheimer’s disease. I suspect, in a similar way to hearing loss, it may be sensory deprivation. A healthy brain is a stimulated brain and reducing visual stimulation culls brain reserve and reduces your threshold for developing dementia.
It will be difficult to do a randomised controlled interventional study, but there may be ways of getting to this using a clever study design.
Lee et al. Association Between Cataract Extraction and Development of Dementia. JAMA Intern Med. 2021 Dec 6;e216990.
Importance: Visual function is important for older adults. Interventions to preserve vision, such as cataract extraction, may modify dementia risk.
Objective: To determine whether cataract extraction is associated with reduced risk of dementia among older adults.
Design, setting, and participants: This prospective, longitudinal cohort study analyzed data from the Adult Changes in Thought study, an ongoing, population-based cohort of randomly selected, cognitively normal members of Kaiser Permanente Washington. Study participants were 65 years of age or older and dementia-free at enrollment and were followed up biennially until incident dementia (all-cause, Alzheimer disease, or Alzheimer disease and related dementia). Only participants who had a diagnosis of cataract or glaucoma before enrollment or during follow-up were included in the analyses (ie, a total of 3038 participants). Data used in the analyses were collected from 1994 through September 30, 2018, and all data were analyzed from April 6, 2019, to September 15, 2021.
Exposures: The primary exposure of interest was cataract extraction. Data on diagnosis of cataract or glaucoma and exposure to surgery were extracted from electronic medical records. Extensive lists of dementia-related risk factors and health-related variables were obtained from study visit data and electronic medical records.
Main outcomes and measures: The primary outcome was dementia as defined by Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition) criteria. Multivariate Cox proportional hazards regression analyses were conducted with the primary outcome. To address potential healthy patient bias, weighted marginal structural models incorporating the probability of surgery were used and the association of dementia with glaucoma surgery, which does not restore vision, was evaluated.
Results: In total, 3038 participants were included (mean [SD] age at first cataract diagnosis, 74.4 (6.2) years; 1800 women (59%) and 1238 men (41%); and 2752 (91%) self-reported White race). Based on 23 554 person-years of follow-up, cataract extraction was associated with significantly reduced risk (hazard ratio, 0.71; 95% CI, 0.62-0.83; P < .001) of dementia compared with participants without surgery after controlling for years of education, self-reported White race, and smoking history and stratifying by apolipoprotein E genotype, sex, and age group at cataract diagnosis. Similar results were obtained in marginal structural models after adjusting for an extensive list of potential confounders. Glaucoma surgery did not have a significant association with dementia risk (hazard ratio, 1.08; 95% CI, 0.75-1.56; P = .68). Similar results were found with the development of Alzheimer disease dementia.
Conclusions and relevance: This cohort study found that cataract extraction was significantly associated with lower risk of dementia development. If validated in future studies, cataract surgery may have clinical relevance in older adults at risk of developing dementia.
General Disclaimer: Please note that the opinions expressed here are those of Professor Giovannoni and do not necessarily reflect the positions of the Barts and The London School of Medicine and Dentistry nor Barts Health NHS Trust and are not meant to be interpreted as personal clinical advice.
Perhaps also simply because cataract extraction = improved visual function meaning higher quality of life (so less depression/anxiety) and more social interaction?