Association of cataract extraction and the risk of dementia—A systematic review and meta-analysis

Authors: Zang Q, Ju Y, Zheng W, Xie L, Wang X, Ren H, Chen Z, Liu X, Bai X, Fan R.

Geographical coverage: China, Japan, the United Kingdom and the United States.

Sector: Impact of cataract extraction

Sub-sector: Risk, health outcomes, dementia

Equity focus: Not reported

Study population: Adults aged 40 and older who underwent or did not undergo cataract surgery

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

Dementia is a major global public health concern with increasing prevalence and substantial social and economic impact. Sensory impairments, including visual loss from cataracts, have been linked to higher dementia risk. Cataract surgery, a widely accessible and effective procedure, may mitigate this risk by improving vision and associated cognitive and social function.

Objective

To assess whether cataract extraction is associated with a reduced risk of all-cause dementia and Alzheimer’s disease.

Main findings

This systematic review and meta-analysis included four cohort studies—three prospective and one retrospective—conducted in China, Japan, the United Kingdom, and the United States. Together, these studies encompassed 245,299 participants, with sample sizes ranging from 3,038 to 226,226. The mean age of participants ranged from 40 to 70 years.

The pooled analysis found that cataract surgery was associated with a statistically significant reduction in the risk of all-cause dementia (odds ratio [OR] = 0.77, 95% CI: 0.66–0.89, P < 0.001). Two studies also examined the risk of Alzheimer’s disease specifically, showing a non-significant trend towards reduced risk (OR = 0.60, 95% CI: 0.35–1.02, P < 0.001). All included studies were rated as high quality using the Newcastle-Ottawa Scale (scores ≥7). Follow-up durations ranged from 8.4 to 10 years. There was moderate statistical heterogeneity (I² = 54.7%). These findings suggest a potential protective effect of cataract surgery against dementia, though interpretation should be cautious due to the small number of included studies and the observational nature of the data.

Methodology: 

Searches were conducted in PubMed, Embase, and the Cochrane Library from inception to 27 November 2022, with no language restrictions. Eligible studies were cohort, cross-sectional, or case-control studies assessing the association between cataract extraction and the risk of all-cause dementia or Alzheimer’s disease. Two reviewers independently screened and extracted data, with a third reviewer resolving any disagreements. Risk of bias was assessed using the Newcastle-Ottawa Scale. Meta-analysis was performed using Stata (version 16), applying random- or fixed-effects models based on heterogeneity. Funnel plots and Egger’s test were used to assess publication bias.

Applicability/external validity:

The included studies spanned four countries with diverse populations and healthcare contexts, enhancing generalisability to high- and middle-income settings. However, the review did not explicitly discuss the applicability across different demographic or socioeconomic groups. There was no stratification by age, gender, ethnicity, or comorbidities. The absence of equity considerations and subgroup analyses limits confidence in the broad applicability of the findings.

Geographic focus:

China, Japan, the United Kingdom, and the United States.

Summary of quality assessment:

There is low confidence in the review’s conclusions due to several important methodological limitations. Although inclusion criteria and risk of bias assessment were appropriate, the search strategy was not comprehensive—grey literature and unpublished studies were not included. Study selection and data extraction were performed independently, but the analytical methods had weaknesses. Unit of analysis errors were not addressed, and no subgroup analyses or meta-regressions were performed. The review also failed to report the impact of study quality on results or stratify findings by risk of bias.