The risk of dementia or cognitive impairment in patients with cataracts: a systematic review and meta-analysis

Author: Wang L, Sang B, Zheng Z.

Geographical coverage: UK, China, the USA, Sweden, and Singapore, as well as one multi-country study covering five low- and middle-income countries (including India and South Africa)

Sector: Cataracts

Sub-sector: Risk factors

Equity focus: Not reported

Study population: Patients with cataracts

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: Cataracts, a major cause of blindness, contribute significantly to global visual impairment and impose a substantial burden on healthcare systems. Adequate vision is vital for maintaining cognitive function, and vision loss from cataracts leads to cognitive decline. Dementia, including Alzheimer’s disease (AD) and vascular dementia (VaD), leads to severe functional impairment and imposes substantial economic costs. Studies have found Alzheimer’s-related biomarkers in the eyes of patients with cataracts, suggesting a possible link between the two conditions. Although other eye diseases such as glaucoma and diabetic retinopathy have been linked to cognitive impairment, systematic reviews on the relationship between cataracts and dementia remain limited. Therefore, this review explores the potential association between cataracts and cognitive decline.

Objective: To determine the association between cataracts and the risk of cognitive impairment or dementia.

Main findings: The review included 11 studies (eight cohort studies and three cross-sectional studies) published between 2012 and 2022. The included studies were conducted in the UK (n=3), China (n=3), the USA (n=2), Sweden (n=1), Singapore (n=1), and a multi-country study (n=1). Quality scores for the 8 cohort studies ranged from 5 to 9, with an average score of 7, indicating high quality overall. Quality scores for the 3 cross-sectional studies ranged from 5 to 8, with 2 studies rated as medium quality and 1 as high quality.

Meta-analysis showed that cataracts were associated with an increased risk of cognitive impairment (odds ratio [OR] = 1.32; 95% confidence interval [CI]: 1.21–1.43; p = 0.0001) and of all-cause dementia (risk ratio [RR] = 1.17; 95% CI: 1.08–1.26; p = 0.0001). Subgroup analyses indicated that having cataracts may increase the risk of AD (hazard ratio [HR] = 1.28; 95% CI: 1.13–1.45; p = 0.0001) and VaD (HR = 1.35; 95% CI: 1.06–1.73; p = 0.015).

Methodology: PubMed, Embase, Web of Science, and the Cochrane Library were searched to identify cohort or cross-sectional studies investigating the relationship between cataracts and the risk of dementia or cognitive impairment. Studies published in English from database inception up to 1 September 2022 were included. The reference lists of the included studies and other relevant meta-analyses were also examined to identify additional studies.

Two reviewers independently screened articles and extracted data, and any discrepancies were resolved by involving a third reviewer. The methodological quality of the included studies was assessed using the Agency for Healthcare Research and Quality (AHRQ) checklist for cross-sectional studies and the Newcastle–Ottawa Scale for cohort studies. Findings were synthesised using either fixed-effect or random-effects meta-analysis models, depending on the level of heterogeneity. Heterogeneity was assessed using the I² statistic, and publication bias was evaluated with a funnel plot and Egger’s regression test. Sensitivity analyses were performed to evaluate the influence of each individual study on the pooled estimates.

Applicability/external validity: The review emphasised the importance of considering the generalisability of the results. Because the included studies were conducted in the USA, the UK, China, Singapore, Sweden, and several low- and middle-income countries, the findings may be subject to regional bias. Additionally, the review noted that only one of the included studies examined gender differences among patients with cataracts. Therefore, further research is needed to determine whether gender influences the association between cataracts and cognitive impairment or dementia.

Geographical focus: The review did not apply any geographical limits. The included studies were conducted in the UK, China, the USA, Sweden, and Singapore, as well as one multi-country study covering five low- and middle-income countries (including India and South Africa).

Summary of quality assessment: Overall, there is medium confidence in this review’s conclusions. The literature search was comprehensive, and inclusion and exclusion criteria were clearly defined. Valid and reliable tools were used to assess the methodological quality of the included studies, and the results of these assessments were reported. Two reviewers independently screened the articles and extracted data. Study characteristics were reported, and a list of included studies was provided. The findings were synthesised using meta-analysis, and sensitivity analyses were conducted to assess the impact of each study on the overall results. Heterogeneity was assessed using the I² statistic. However, no list of excluded studies was provided. The review limited its search to English-language publications only. Moreover, the findings were not reported by risk-of-bias.