Cataract Extraction and Dementia Risk Reduction: Clinical Observations

Dementia affects almost 50 million people worldwide and there are no effective treatments. Efforts to reduce the risk or delay the onset of dementia are increasingly important, as noted in the recent 2020 Lancet Commission report.

Twenty percent of adults over age 65 in the United States experience significant sensory impairment, such as vision or hearing loss, even with correction. 2 Addressing the sensory loss that affects a substantial portion of older adults may be a potentially modifiable risk factor for dementia in later life.

Because sensory impairments and dementia are strongly associated with aging, increased knowledge about the association between sensory impairment and dementia may have important implications for individual and global public health, particularly if interventions to improve sensory function reduce the risk of dementia.

Visual impairment is a major risk for dementia. Cataract is a leading cause of blindness worldwide, affecting more than 35 million people worldwide and causing blindness in approximately 20 million.

Cataract affects most older adults at risk of dementia.

However, there are conflicting results regarding the association between cataract extraction and cognitive decline or dementia.

We hypothesized that older adults with cataracts who undergo cataract extraction may have a lower risk of developing dementia compared to participants who do not undergo cataract surgery or participants who undergo other eye procedures that They do not restore vision, like glaucoma surgery.

Previous studies exploring this association have been limited by small sample sizes, cross-sectional designs, and variable qualities of dementia assessment. More importantly, these studies have not taken into account healthy patient bias (i.e., when surgery is more likely in healthier individuals with the same cataract severity).

To our knowledge, no studies have compared the associations between cataract extraction and dementia with other ophthalmic surgical procedures. To address potential healthy patient bias, we included glaucoma surgery in our analyses. We used extensive data from the Adult Changes in Thought (ACT) study to address these questions.

We examined whether cataract extraction was associated with a lower risk of dementia and used the same modeling approach to examine whether glaucoma surgery was associated with a lower risk of dementia.

Importance  

Visual function is important for older adults. Interventions to preserve vision, such as cataract extraction, can modify the risk of dementia.

Aim  

To determine whether cataract extraction is associated with a reduced risk of dementia among older adults.

Design, environment 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 free of dementia at the time of enrollment and were followed every two years until incident dementia occurred (all-cause, Alzheimer’s disease, or Alzheimer’s disease and dementia related).

Only participants who had a diagnosis of cataract or glaucoma before enrollment or during follow-up were included in the analyzes (i.e., a total of 3038 participants).

The data used in the analyzes was collected from 1994 to September 30, 2018, and all data was analyzed from April 6, 2019 to September 15, 2021.

Exhibitions  

The primary exposure of interest was cataract extraction. Data on cataract or glaucoma diagnosis 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 results 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 analyzes were performed 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 assessed.

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 a significant risk reduction (hazard ratio, 0.71; 95% CI, 0.62-0.83; P < .001). of dementia compared to 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 had no significant association with dementia risk (hazard ratio, 1.08; 95% CI, 0.75-1.56; P = 0.68). Similar results were found with the development of Alzheimer’s disease dementia.

Discussion

Several hypothesized mechanisms may underlie the association between cataract extraction and dementia risk. Visual impairment can lead to psychosocial difficulties, withdrawal from social interactions, and reduced activity or exercise, all of which are associated with cognitive decline.

Cataract-related visual impairment may decrease neuronal input, potentially accelerating neurodegeneration or magnifying the effect of neurodegeneration through cortical atrophy.

The visual cortex undergoes structural changes with vision loss.

For patients with neovascular age-related macular degeneration, vision loss was associated with atrophy of the visual cortex during a 5-year follow-up, and an increase in gray matter volume has been observed after cataract surgery . Finally, compensation for the deficit of visual information can increase cognitive load and exacerbate cognitive decline.

The lower risk of developing dementia after cataract extraction may also be associated with greater quantity and quality of light. Intrinsically photosensitive retinal ganglion cells (ipRGCs), which are exquisitely sensitive to short wavelength (blue) light, have been shown to be associated with cognitive function, circadian rhythm, and AD.

ipRGCs project to multiple brain areas and their excitation can trigger widespread cortical activity. The yellow hue of age-related cataracts blocks blue light. Therefore, another potential mechanism by which cataract extraction is associated with a reduced risk of dementia is the facilitation of ipRGC stimulation by blue light.

We must recognize that our results could be explained by unmeasured or residual confounding factors , like any observational study. There were some suggested differences between people who had cataract surgery and those who did not, but controlling for a broad spectrum of factors underlying these differences between people with and without surgery did not significantly change our findings.

We also compared the outcomes of cataract surgery with those of glaucoma surgery in the same cohort. In essence, we used glaucoma surgery as a negative control. It is true that the 2 surgical procedures have different indications, so the comparison is only a rough approach to address the possibility of healthy patient bias.