The association between cataract and incidence of cognitive impairment in older adults: A systematic review and meta-analysis

Author: Xiong Z, Li X, Yang D, Xiong C, Xu Q, Zhou Q.

Geographical coverage: The United States, China, the United Kingdom, and Sweden, with one study spanning six countries.

Sector: Cataracts

Sub-sector: Risk Factors

Equity focus: Not reported

Study population: Patients with cataract

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: Globally, dementia affects over 50 million people, and that figure is expected to triple by 2050, posing a serious social and economic burden. While incidence has declined in some Western countries, it continues to rise in parts of Asia, highlighting the importance of addressing modifiable risk factors. Visual impairment, particularly from cataracts, contributes to cognitive decline through mechanisms such as reduced sensory input, social isolation, depression, and physical inactivity. Cataracts are prevalent in older adults and can impair quality of life and cognitive function. Although some studies have suggested a link between cataracts and cognitive impairment, their findings have been inconsistent and limited by methodological issues. Therefore, this study was conducted to better understand the relationship between cataracts and cognitive impairment.

Objectives: To examine the association between cataracts and the risk of cognitive impairment in older adults.

Main findings: The review included 13 observational studies comprising 798,694 participants. Among these, nine were prospective, two were retrospective, and two were cross-sectional. The included studies were conducted in the United States (n=4), the United Kingdom (n=2), China (n=5), Sweden (n=1), and one was a multi-country study (n=1). Regarding methodological quality, five studies had a substantial overall risk of bias. Nevertheless, the overall quality of evidence from the meta-analysis was generally good.

Participants with cataracts were found to have an increased risk of developing all-cause dementia compared with those without cataracts (pooled hazard ratio [HR]: 1.22; 95% confidence interval [CI]: 1.08 to 1.38, I² = 81.7%). Similarly, having cataracts was associated with a higher risk of Alzheimer’s disease dementia (pooled HR: 1.18; 95% CI: 1.07 to 1.30, I² = 45.2%). An elevated risk was also observed for vascular dementia (pooled HR: 1.21; 95% CI: 1.02 to 1.43, I² = 0%). Additionally, individuals with cataracts had a significantly increased risk of developing mild cognitive impairment (pooled HR: 1.30; 95% CI: 1.13 to 1.50, I² = 0%). However, no significant association was found between cataracts and mixed dementia (pooled HR: 1.03; 95% CI: 0.52 to 2.04, I² = 77.9%).

Methodology: Searches were conducted in MEDLINE, Embase, and Web of Science from inception to January 2023 to identify observational studies conducted among community-dwelling older adults with no specific risk factors for cognitive impairment. Studies were included if they were published in English and evaluated cognitive function using validated cognitive tests, physician diagnoses, or self-reported measures. In addition, Google Scholar was used to identify further relevant research through the reference lists of the included studies.

Two reviewers independently screened the studies and extracted data. Any disagreements were resolved through discussion or by consulting a third reviewer. The same two reviewers also independently assessed the risk of bias of the included articles using the Newcastle-Ottawa Scale, resolving any discrepancies through discussion or with a third reviewer.

The findings were synthesised using a random-effects model meta-analysis. Sensitivity analyses were conducted to examine the effect of each individual study on the pooled estimates, and subgroup analyses were performed to determine whether the results were influenced by other variables. Heterogeneity was assessed using the I² statistic, and publication bias was evaluated using funnel plots.

Applicability/external validity: The review did not discuss the applicability or external validity of its findings.

Geographic focus: The authors did not apply any geographic limits. The included studies were conducted in the United States, China, the United Kingdom, and Sweden, with one study spanning six countries.

Summary of quality assessment: Overall, there is medium confidence in the conclusions of this review. The literature search was comprehensive, and inclusion and exclusion criteria were clearly defined. Two reviewers independently screened studies, extracted data, and assessed risk of bias using established tools, resolving any disagreements through discussion or consultation with a third reviewer. Characteristics of the included studies were well documented, the meta-analyses were appropriately performed, and heterogeneity was addressed. However, the search was limited to English-language publications; the review did not provide a list of excluded studies; and the findings were not reported according to the risk of bias of the included studies.