Blindness in glaucoma: primary open-angle glaucoma versus primary angle-closure glaucoma – a meta-analysis

Authors: George R, Panda S, Vijaya L.

 

Geographical coverage: India, China, Nepal, Bangladesh, Japan, Myanmar, Korea, Brazil, USA, Singapore and Iran.

Sector: Burden of disease

Sub-sector: Epidemiology

Equity focus: Not reported

Study population: Patients with glaucoma

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

Glaucoma remains the leading cause of irreversible blindness globally and typically presents in two primary forms: primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG). Among these, PACG is often considered more aggressive due to its mechanisms involving pupillary block, which can cause acute or chronic elevations in intraocular pressure (IOP), optic nerve damage, and synechial angle closure. The disease has a disproportionate impact on Inuit and Asian populations, accounting for approximately forty percent of all primary glaucoma cases in these regions. Despite its significant burden, inconsistencies in how population-based studies report prevalence, blindness rates, and angle-closure definitions have made it challenging to fully assess PACG’s impact relative to POAG.

Objectives

The aim of this study was to quantify the relative risk of blindness associated with PACG compared to POAG. This was achieved by analysing population-based studies that reported blindness rates for both conditions within the same cohort.

Main findings

The meta-analysis included twenty-three population-based studies involving a total of 78,434 individuals. Within these, 1,702 people were diagnosed with POAG, among whom 151 individuals, or 8.9 percent, were blind. In contrast, 724 individuals were diagnosed with PACG, of whom 196, or 27.0 percent, were blind. The calculated risk ratio (RR) for blindness in PACG compared to POAG ranged from 0.73 to 10.6 across the studies, with a pooled RR of 2.39 and a 95 percent confidence interval (CI) of 1.99 to 2.87. This indicates that individuals with PACG are more than twice as likely to be blind as those with POAG. Subgroup analyses confirmed the consistency of this pattern across both rural and urban settings, with RRs of 2.37 and 2.65, respectively. Further comparisons between studies that defined blindness using visual field restriction and those using best-corrected visual acuity found similar results, with RRs of 1.92 and 2.64 (P = 0.11). Additionally, the way angle closure was defined—whether using more than two quadrants or three or more quadrants of iridotrabecular contact—had minimal effect on the comparative risk (RRs of 2.79 vs. 2.25).

Methodology

A comprehensive search was conducted in PubMed to identify population-based studies published in English between 2000 and 2020. Eligible studies used random or cluster sampling and reported both prevalence and blindness outcomes for POAG and PACG, based on ISGEO definitions. Two independent reviewers screened the articles and extracted relevant data. Discrepancies were resolved through discussion. Reference lists of included studies were also reviewed for additional eligible publications. A random-effects model meta-analysis was conducted to synthesise the risk ratios, and heterogeneity was assessed using the I² statistic. The risk of bias was evaluated using a modified Leboeuf-Yde and Lauritsen tool, and the certainty of evidence was assessed using the GRADE approach. The authors reported no significant heterogeneity (I² = 0%) and rated the certainty of evidence as high.

Applicability and external validity

Most of the studies included in the analysis were conducted in Asian countries, which may limit the generalisability of the findings to populations in other geographic regions. Additionally, relatively few studies from Western countries reported a substantial number of PACG cases, further limiting comparative assessments of blindness risk across different populations.

Geographic focus

The included studies were conducted in India, China, Nepal, Bangladesh, Japan, Myanmar, Korea, Brazil, the United States, Singapore, and Iran.

Summary of quality assessment

Although the review followed a rigorous methodology, some limitations should be noted. The search was limited to English-language studies indexed in PubMed, and no attempt was made to include grey literature or non-English publications. While the study quality was assessed using a validated tool, the number of reviewers involved in the data extraction was not clearly reported. The authors did not provide a list of excluded studies or indicate whether original study authors or subject matter experts were consulted for additional insights.

Publication Source:

George, R., Panda, S., & Vijaya, L. (2022). Blindness in glaucoma: primary open-angle glaucoma versus primary angle-closure glaucoma-a meta-analysis. Eye (London, England), 36(11), 2099–2105. link 

 

Downloadable link