Methodological quality of the review: Medium confidence
Author: Wang W, He M, Zhou M, Zhang X
Geographical coverage: Canada, Israel and Spain
Sub-sector: Open angle glaucoma
Equity focus: Not specified
Review type: Effectiveness review
Quantitative synthesis method: Meta-analysis
Qualitative synthesis method: Not applicable
Background: Globally, glaucoma is a leading cause of irreversible blindness. Lowering the intra-ocular pressure (IOP) is still the most effective way to prevent its development and progression, for which, there are three methods: medical treatment, laser therapy and surgical intervention.
There are different types of laser therapy available such as selective laser trabeculoplasty (SLT) and argon laser trabeculoplasty (ALT), for which many randomised controlled trials (RCTs) have been published. However, a quantitative assessment of all published RCTs is not available. Therefore, the aim of this study was to assess the efficacy and tolerability of both procedures in the treatment of open angle glaucoma (OAG).
Objectives: To examine possible differences in clinical outcomes between SLT and ALT in OAG at different times post-treatment.
Main findings: In this study, a total of six RCTs involving 482 eyes treated with laser trabeculoplasty were included. Of the six studies, four were conducted in Canada, one in Israel and one in Spain.
Findings showed that for all patients (including first and previous laser trabeculoplasy), no significant difference in IOP lowering was observed between SLT and ALT at one hour (P = 0.40), one week (P = 0.72), one month (P = 0.37), six months (P = 0.08), one year (P = 0.34), two years (P = 0.58), three years (P = 0.34), four years (P = 0.47), and five years (P = 0.50).
A statistically significant difference in favour of SLT was found when comparing the IOP reduction at three months after intervention (weighted mean difference (WMD): 1.19 mm Hg [0.41; 1.97]; I2=0%; P = 0.003). For patients who were naive to laser, there was no significant difference of reduction in IOP comparing SLT with ALT at any time point. In patients’ previous LT, no statistically significant difference in IOP reduction was found at six months (WMD: 1.92 mm Hg [-0.91; 4.74]; I2 = 77.3%; P = 0.18).
There was no significant difference in the reduction in the number of glaucoma medications, the success rate or adverse event rates between the two treatments. A funnel plot based on IOP reduction at six months was created. The relatively symmetrical distribution suggests the absence of publication bias despite the small number of trials that were included in this meta-analysis.
Based on these findings, authors conclude that SLT has equivalent efficacy to ALT with a similar constellation of side effects. In the case of retreatment, SLT appears to be similar to ALT in IOP-lowering at six months. In general, authors report included trials to be of good quality for most of the aspects evaluated. Authors note the need for large-scale, well designed RCTs.
Methodology: The guide for this study was the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).
The following databases were searched up to August 2013: PUBMED, EMBASE, the Web of Science, the Chinese Biomedicine Database and the Cochrane Controlled Trials Register. For additional studies, authors also searched websites of professional associations and Google Scholar. References of included studies were also reviewed. No restriction was applied for language or year of publication. Eligible studies were prospective RCTs comparing the use of ALT and SLT in adult patients with any form of OAG.
Selection, data collection and assessment of the methodological quality of the studies were conducted independently by two reviewers. The quality assessment was performed according to the risk of bias tool outlined in the Cochrane Handbook for Systematic Reviews of Interventions (version 5.1.0). All analyses were performed on an intent-to-treat basis. The weighted mean difference (WMD) was calculated for continuous outcomes. For dichotomous outcomes, the relative risk (RR) was estimated. All results were given with 95% confidence intervals (CIs). Heterogeneity was checked using Cochran’s Q statistic and the P-value. I2 metrics, which quantify heterogeneity irrespective of the number of studies, were also reported.
Applicability/external validity: Authors note that studies included in the review are not sufficient to examine the secondary outcomes since they were not the primary outcomes and were only clinically significant endpoints consistently reported in many of the studies analysed in the meta-analysis. As such, results are not conclusive.
Geographic focus: Studies included in the review were conducted in Israel, Canada and Spain. Authors note that findings are inconclusive.
Summary of quality assessment: Authors conducted searches of relevant databases avoiding language bias and searches on reference lists of relevant studies. Two researchers independently examined the title and abstract of each paper. Overall, the method used to analyse findings is clearly reported and limitations are appropriately acknowledged by the reviewers. However, authors did not contact experts/authors for further additional studies to ensure that relevant studies were not omitted. Thus, a medium confidence was attributed to the conclusion about the effects of this review.