Methodological quality of the review: Medium confidence

Author: Zhao D, Cho J, Kim MH, Guallar E

Geographical coverage: Asia, United States of America (USA), Europe, West Indies, Australia, Canada, Middle East and Congo

Sector: Glaucoma

Sub-sector: Primary open angle glaucoma

Equity focus: Adults

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: More than 60 million people are affected by glaucoma worldwide. The most common type of glaucoma is primary open angle glaucoma (POAG), which is influenced by demographic factors such as age, race and family history, and by several ocular parameters. Increased intra-ocular pressure (IOP) is the most important modifiable risk factor for POAG, but there is substantial interest in identifying other potentially modifiable risk factors.

Objectives: To estimate the association between blood pressure levels and hypertension with POAG and IOP by conducting a systematic review and meta-analysis of available literature.

Main findings: Overall, authors included sixty observational studies in the review (44 cross-sectional, nine case-control and seven longitudinal cohort studies). Twenty-six studies were performed in Asia, 13 in the USA, nine in Europe, three in the West Indies, three in Australia, three in Canada, two in the Middle East and one in Congo.

The pooled relative risk for POAG comparing patients with hypertension to those without hypertension was 1.16 (95% CI = 1.05–1.28), with modest heterogeneity across studies (I2 34.5%). Virtually all studies reported a positive association between blood pressure and IOP. The pooled average increase in IOP associated with a 10 mm Hg increase in systolic blood pressure was 0.26 mm Hg (95% CI 0.23–0.28, I2 30.7%), and the average increase associated with a 5 mm Hg increase in diastolic blood pressure was 0.17 mm Hg (95% CI 0.11–0.23, I2 90.5%).

Authors conclude that hypertension was associated with increased IOP. The association between hypertension and POAG was stronger in cross-sectional compared with case-control and longitudinal studies. The findings of this study support a role of increased blood pressure in elevated IOP and possibly in the development of glaucoma.

Methodology: Medline and EMBASE were searched for observational studies investigating the relationship of blood pressure or hypertension with POAG, IOP or ocular hypertension (OHT) without restrictions on language or publication date. Key words included: systolic blood pressure, diastolic blood pressure, blood pressure, hypertension, intraocular pressure, intraocular tension, eye pressure, eyeball pressure, eye internal pressure, intraorbital pressure, ocular pressure, ocular tension, intraocular hypertension, intraocular tension and glaucoma.

The reference lists of relevant articles were searched for other articles. The following exclusion criteria were applied:

(a) Reviews, editorials or letters

(b) Case reports or case series

(c) Studies not conducted in humans

(d) Studies not conducted in adults

(e) Studies conducted in population samples comprised only of patients with established glaucoma or ocular hypertension at baseline

(f) Studies not reporting glaucoma, IOP or OHT outcomes

(g) Studies not using blood pressure or hypertension as exposure

(h) Studies investigating mainly drug effects or metabolism

(i) Studies of populations with specific conditions (e.g. pregnancy or eye surgery) that limit their generalizability to general population samples.

Two reviewers independently reviewed all search results to identify eligible papers and abstracted data from selected studies. In addition, authors critically appraised included studies. Data was then analysed and meta-analysis was conducted.

Applicability/external validity: Authors did not discuss applicability/external validity.

Geographic focus: Authors included studies from low, medium and high-income countries. However, authors did not discuss the applicability of findings to low and middle-income countries.

Summary of quality assessment: Overall, there is medium confidence in the conclusions of the review. Review authors used appropriate methods to screen studies for inclusion, extract data, critically appraise and analyse findings of included studies. However, authors did not conduct a comprehensive search of the literature to ensure that unpublished studies were included in the review.