Meta-analysis of selective laser trabeculoplasty versus topical medication in the treatment of open-angle glaucoma

Methodological quality of the review: Low confidence

Authors: Li X, Wang W, Zhang X

Region: USA, China, Canada and UK

Sector: Open angle glaucoma

Sub-sector: Treatment

Equity focus: None specified

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

The introduction of selective laser trabeculoplasty (SLT) provided a new non-invasive choice for the reduction of intraocular pressure (IOP) in eyes with open-angle glaucoma (OAG). This treatment consists of the application of laser spots in the trabecular meshwork which leads to an increase in the outflow facility and, consequently, decreases IOP.

Objectives:

The aim of this study was to examine possible differences in clinical outcomes between SLT and topical medication in the treatment of open-angle glaucoma.

Main findings:

In total, the authors included five studies in the meta-analysis. One study was prospective non-randomized comparative trial and four studies were randomized clinical trials. One study was conducted in the USA, one in China, one in Canada and two in the UK. The Downs and Blacks score for each study exceeds 16, which indicates adequate methodological quality.

There was a total of 492 eyes of 366 patients with open-angle glaucoma. Four studies involving 325 eyes compared SLT with medication in terms of the IOPR. The authors reported the weighted mean difference (WMD) of the IOPR from the baseline was 0.6 (95 % confidence intervals: −0.24,1.43) when comparing SLT with medication. Authors found no statistical heterogeneity between studies (χ2 = 1.30, P = 0.75, I2 = 0.0 %). All five studies reported success rates, with a pooled OR of 0.84 (95 % confidence intervals: 0.42, 1.68), which was not statistically significant. No statistical heterogeneity was observed between studies (χ2 = 5.98, P = 0.200, I2 = 33.1 %). Subgroup and sensitivity analysis confirmed the high stability of the meta-analysis results.

The authors concluded that both SLT and topical medication demonstrate similar success rates and effectiveness in lowering intraocular pressure in patients with open-angle glaucoma.

Methodology: 

The authors searched PubMed, Embase, the Web of Science, the Chinese Biomedicine Database, and the Cochrane Controlled Trials Register database from their inception up to March 2014. No restriction was applied for language or year of publication. The websites of professional associations and Google Scholar were also searched for additional information. Moreover, a manual search was performed by checking the reference lists of all retrieved trials. Eligible studies were prospective randomized or non-randomized comparative controlled trials, which compared the use of SLT and topical anti-glaucoma medications in adult patients with any form of naïve OAG or ocular hypertension.

To assess the quality of included studies, the authors used the Downs and Blacks scale, which could evaluate both randomized and non-randomized studies. The system comprises 27 items distributed between five subscales regarding reporting (10 items), external validity (three items), bias (seven items), confounding (six items), and power (one item). Studies’ methodological quality was assessed as excellent, good, fair, or poor when the total score was ≥20, from 15 to 19, from 11 to 14, and ≤10, respectively.

Intention-to-treat analyses were used in each outcome in the statistical analysis. Data was combined using inverse variance random-effects model regardless of heterogeneity. The weighted mean difference was calculated for continuous outcomes while the odds ratio was estimated for dichotomous outcomes. The authors checked heterogeneity using Cochran’s Q statistics and the P-value. I² metrics, which quantify heterogeneity irrespective of the number of studies, were also reported.

The authors also performed subgroup analysis and investigated the influenced of a single study on the overall pooled estimates by omitting study in each turn. Publication bias was assessed visually examining asymmetry in funnel plots.

Applicability/external validity:

The authors note that the results reveal that SLT is as effective as medication in regard to the control of IOP, which is consistent with a previous review.

Geographic focus

The authors only included studies conducted in high-income countries as studies from low- and middle-income countries were either not eligible or not available.

Summary of quality assessment:

Overall, low confidence was attributed in the conclusions about the effects of this study. Although the authors used appropriate methods to analyse findings of the review, it is not clear if methods used to conduct the review (for example, screen studies and extract data of included studies) were rigorous enough to avoid bias.