Cataract surgery and cognitive benefits in the older person: a systematic review and meta-analysis

Author: Yeo BSY, Ong RYX, Ganasekar P, Tan BKJ, Seow DCC, Tsai ASH.

Geographical coverage: United States, Japan, Australia, England, China, Finland, Iran, Italy, and Taiwan.

Sector: Cataract surgery

Sub-sector: Risk factors

Equity focus: Not reported

Study population: Adults aged 18 years and above with cataracts

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

According to the Global Burden of Disease Study 2019, 57.4 million cases of dementia were identified worldwide in 2019, and this number is expected to increase to 152.8 million by 2050. The link between vision impairment and cognitive decline is well-documented. However, the cognitive advantages of cataract surgery remain unclear. With no cure for dementia, identifying modifiable risk factors is crucial in the care of patients with cognitive impairments.

Objective:

To determine the association of cataract surgery with cognitive impairment and dementia.

Main findings:

Overall, authors found that cataract surgery is associated with a significant improvement in short-term cognitive test scores for patients with normal cognition and a reduced risk of long-term cognitive impairment and dementia. The review included 24 studies in the qualitative analysis and 19 in the meta-analysis. Most were cohort studies, with one RCT. Geographically, studies spanned Europe, North America, Asia, and Australia. Eleven observational studies had low risk of bias; 12 had moderate risk. The RCT had a low risk of bias.

Meta-analysis showed a 4% improvement in short-term cognitive test scores post-surgery (RoM, 0.96; 95% CI, 0.94–0.99; I² = 75%) and a 25% reduced risk of long-term cognitive impairment and dementia compared to untreated patients (HR, 0.75; 95% CI, 0.72–0.78; I² = 9%). No significant difference was found compared to healthy controls.

Future research should explore heterogeneity causes and confirm long-term benefits using consistent cognitive assessments.

Methodology: 

The authors searched several databases including PubMed, Embase, and The Cochrane Library up to September 5, 2022, to find research on how cataract surgery affects cognitive function, cognitive decline, cognitive impairment, and dementia. Two authors independently reviewed study titles, abstracts, and full texts to determine eligibility, resolving disagreements with a third author. The research focused on adults with cataracts who underwent surgery compared to those with untreated cataracts and healthy controls. They included single-arm studies that compared cognitive outcomes before and after surgery. Key outcomes were the risk of cognitive impairment or dementia over time and the impact on short-term cognitive test scores. Cognitive function was measured using tests like the Mini-Mental State Examination (MMSE).

Data was extracted by two authors, including study details, demographics, and follow-up duration. Bias was assessed using the Newcastle-Ottawa Scale (NOS) for observational studies and the Cochrane risk-of-bias tool for randomised trials (RoB 2). Publication bias was evaluated through funnel plot asymmetry and Egger’s test if there were at least ten studies per outcome. The Grading of Recommendations, Assessment, Development and Evaluations (GRADE) framework assessed the overall quality of evidence. Meta-analysis was performed using R Studio, pooling adjusted hazard ratios (HRs) to determine risks of cognitive impairment and dementia. Subgroup analyses by cognitive outcome type and continent were conducted, and the ratio of means (RoM) of cognitive test scores before and after surgery was pooled. Statistical heterogeneity was assessed using I² and Cochran Q test values, adopting a random-effects model for all analyses, with significance set at P ≤ 0.05.

Applicability/external validity:

Studies came from varied geographical backgrounds, improving generalisability. However, variability in cognitive assessments and follow-up durations limits consistency and generalisability. No theory-based framework was used to assess applicability.

Geographic focus:

Included studies were conducted in the United States, Japan, Australia, England, China, Finland, Iran, Italy, and Taiwan.

Summary of quality assessment:

Overall, there is low confidence in the review’s conclusions due to methodological limitations. The search strategy may have missed relevant studies, and subgroup analyses by risk of bias were not conducted.