Methodological quality of the review: Low confidence

Authors: Bae HW, Lee N, Lee HS, Hong S, Seong GJ, Kim CY

Region: USA, Italy, India, Australia, Japan, Netherlands, Barbados, China, Singapore and Greece

Sector: Open-angle glaucoma

Sub-sector: Hypertension, risk

Equity focus: None specified

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

Systemic hypertension is thought to increase the risk for developing open-angle glaucoma (OAG) through several mechanisms. However, previous epidemiological studies have shown conflicting results regarding this potential association.

Objectives:

To investigate the association between OAG and hypertension.

Main findings:

The authors included 16 studies in the meta-analysis with a total of 60,084 subjects. The studies were published between 1995 and 2012, and all studies were population-based: 15 were cross-sectional studies and one was a longitudinal cohort study. Nine studies were performed on Asian populations and seven investigated Western populations. Hypertension was defined based on the use of anti-hypertensive medication and/or the actual BP in all studies. Two studies indicated the odds ratios (ORs) for OAG, high-tension glaucoma (HTG), and normal-tension glaucoma (NTG), while the remaining studies presented the OR for OAG only.

The authors note that the forest plot and I² showed statistically significant homogeneity ((I²= 7.5%, P= 0.37) among all included studies for OAG. The pooled OR was 1.22 (95% CI: 1.09–1.36) using the fixed-effects model and 1.22 (95% CI: 1.08–1.37) using the random-effects model. Based on the sensitivity analysis showed that no study had a strong influence on the pooled OR in this meta-analysis and the funnel plot and Egger’s regression test (P=0.90) indicated no obvious evidence of publication bias. Meta-regression analysis showed no significant association between age and pooled OR (P= 0.28).

For the subgroup analysis, the pooled OR for HTG (heterogeneity; I² = 0.0%) was 1.92 (95% CI: 1.28–2.87) using the fixed-effects model, whereas that of NTG (heterogeneity; I² = 28.4%) was 0.99 (95% CI: 0.68–1.45) using the fixed-effects model and 0.94 (95% CI: 0.56–1.58) using the random-effects model. The pooled OR from Asian populations (heterogeneity; I² = 26.6%) was 1.20 (95% CI: 1.01–1.43) using the fixed-effects model and 1.19 (95% CI: 0.97–1.46) using the random-effects model, whereas that from Western populations (heterogeneity; I² = 0.0%) was 1.23 (95% CI: 1.06–1.43) using the fixed-effects model. The authors found no evidence of publication bias was detected by Egger’s regression test (P= 0.76 and 0.46, respectively) or the funnel plot.

Methodology:  

Two authors independently conducted literature searches on PubMed and Embase for literature published before 31st March 2014. The authors used the following search terms: (‘‘hypertension’’[MeSH Terms] OR ‘‘hypertension’’[All Fields]) AND (‘‘glaucoma’’[MeSH Terms] OR ‘‘glaucoma’’). In addition, the reference lists of all identified articles were examined.

The authors defined OAG as the presence of glaucomatous optic disc in the review.

Inclusion criteria consisted of studies that were population-based, evaluated hypertension and OAG, and reported odds ratios (ORs) with 95% confidence intervals (CI) to measure the association between hypertension and OAG or showed the raw data in the article to calculate the OR with 95% CI.

Studies were excluded from this meta-analysis if they were not reported in English, did not include hypertension as a risk factor for OAG, covered angle-closure glaucoma or secondary glaucoma or did not clearly designate OAG, or defined hypertension or glaucoma based only medical records, questionnaire, or self-reported history.

Data were extracted from studies by two authors independently, disagreement was settled by discussion between the authors. The study quality was assessed by inverse-variance weighting. The authors estimated the pooled ORs with 95% CIs using the fixed- and the random-effects models. Publication bias was evaluated using Egger’s regression test and/or a funnel plot. In addition, the authors performed meta-regression analysis using age, which could affect the prevalence of both hypertension and OAG. Subgroup meta-analysis was carried out in the review to evaluate each pooled OR in more homogeneous subgroups and to identify characteristics of the association between hypertension and OAG.

Applicability/external validity:

Systemic hypertension increases the risk for developing OAG, especially in those with HTG.

Geographic focus:
The authors reported pooled OR from Asian populations (heterogeneity; I² = 26.6%) was 1.20 (95% CI: 1.01–1.43) using the fixed-effects model and 1.19 (95% CI: 0.97–1.46) using the random-effects model, whereas that from Western populations (heterogeneity; I² = 0.0%) was 1.23 (95% CI: 1.06–1.43) using the fixed-effects model.

Summary of quality assessment:

Overall, low confidence was attributed in the conclusions about the effects of this review. The authors did not conduct a thorough search of the literature to ensure that relevant literature was identified and included in the review. The authors did not search for unpublished/grey literature and restricted to the inclusion of studies written in English only. In addition, the authors did not assess the risk of bias of included studies which impact on the reliability of the overall findings of the review.