Aqueous shunts for glaucoma (review)

Title: Aqueous shunts for glaucoma (review)

Methodological quality of the review: High confidence

Authors: Tseng VL, Coleman AL, Chang MY, Caprioli J

Region: Brazil, Canada, Singapore, UK, USA, Chile, Mexico, Korea, Egypt, Iran, India

Sector: Treatment

Sub-sector: Shunts

Equity focus:  None specified

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

Glaucoma is a condition caused by the build-up of fluid in the front part of the eye. This build-up of fluid raises the eye pressure, which can lead to damage of the optic nerve and vision loss. Some people with glaucoma need surgery to reduce eye pressure. Standard surgery is called trabeculectomy. In trabeculectomy, a small hole is made to the tissue in the front of the eye to create a drain for the fluid. Alternatively, a small implant called an aqueous shunt can be inserted into the eye to create a pathway for fluid to drain.

Objectives:

To assess the effectiveness and safety of aqueous shunts for reducing intraocular pressure (IOP) in glaucoma compared with standard surgery, another type of aqueous shunt, or modification to the aqueous shunt procedure.

Main findings:

The authors included a total of 27 trials, where seventeen studies reported adequate methods of randomization, and seven reported adequate allocation concealment.

The authors noted that four trials compared an aqueous shunt with trabeculectomy, of which three reported one-year outcomes. Overall, evidence from these trials were of very-low certainty. The authors noted that the difference in logMAR visual acuity was uncertain (mean difference (MD) 0.12 units, 95% confidence interval (CI) -0.07 to 0.31; 380 participants. In two trials, the authors noted that the difference in visual field score was uncertain (MD -0.25, 95% CI -1.91 to 1.40; 196 participants). The mean number of antiglaucoma medications was higher in the aqueous shunt group than the trabeculectomy group in one trial (MD 0.80, 95%CI 0.48 to 1.12; 184 participants. The authors observed that the effect on needing additional glaucoma surgery was uncertain between groups in two trials (risk ratio (RR) 0.24, 95% CI 0.04 to 1.36; 329 participants). In one trial, the authors reported fewer total adverse events were reported in the aqueous shunt group than the trabeculectomy group (RR 0.59, 95% CI 0.43 to 0.81; 212 participants) No trial reported quality-of-life outcomes at one-year follow-up.

The authors found some differences between different implants: the Baerveldt and Molteno implants may work better than the Ahmed implant; eye pressure was reduced more and fewer antiglaucoma medications were needed (moderate- and low-certainty evidence). The Molteno implant may work better than the Schocket implant (MD -2.50 mmHg, 95% CI -4.60 to -0.40; 115 participants; low-certainty evidence on eye pressure only).

The remaining 18 trials evaluated modifications to aqueous shunts, including 14 trials of Ahmed implants (early aqueous suppression versus standard medication regimen, two trials; anti-vascular endothelial growth factor agent versus none, four trials; corticosteroids versus none, two trials; shunt augmentation versus none, three trials; partial tube ligation versus none, one trial; pars plana implantation versus conventional implantation, one trial; and model M4 versus model S2, one trial); one trial of 500 mm2 Baerveldt versus 350 mm2 Baerveldt; and three trials of Molteno implants (single-plate with oral corticosteroids versus single-plate without oral corticosteroids, one trial; double-plate versus single-plate, one trial; and pressure-ridge versus double-plate with tube ligation, one trial).

Based on these findings, the authors note that information was insufficient to conclude whether there are differences between aqueous shunts and trabeculectomy for glaucoma treatment.

Methodology: 

Inclusion criteria consisted of randomized controlled trials that compared various types of aqueous shunts with standard surgery or to each other in eye with glaucoma. In this review, the authors assessed the following comparisons

1) Aqueous shunts compared with trabeculectomy,

2) Aqueous shunts compared with another aqueous shunt and

3) Aqueous shunts compared with and without modification.

Primary outcome measures included control of IOP (mean decrease from baseline and proprorion meeting IOP thresholds).

The authors searched CENTRAL, MEDLINE Ovid, Embase.com, PubMed, LILACS, ClinicalTrials.gov, and the World Health Organization International Clinical Trials Registry Platform. They did not use any date or language restrictions in the electronic search for trials. They last searched the electronic databases on 15 August 2016. In addition, the reference lists of identified trial reports and the Science Citation Index were also searched to find additional trials.

Two reviewers independently screened studies for inclusion in the review, extracted data and assessed risk of bias of included studies.

For dichotomous outcomes the authors calculated risk ratios with 95% confidence intervals. Dichotomous outcomes included the proportion meeting certain IOP thresholds, the proportion undergoing additional glaucoma surgery, and the proportion with adverse events.

The authors assessed for methodological and clinical heterogeneity by comparing study designs, participants, interventions, and outcomes across studies. When they identified no methodological or clinical heterogeneity, they combined quantitative outcome data and examined the I² value and tested for statistical heterogeneity using the Chi² test. To assess for selective reporting bias, the authors compared pre-specified outcomes in study protocols and trial registry records. In terms of data synthesis, they planned to use a random-effects model when three or more trials were included in a meta-analysis, and a fixed-effects model when fewer than three trials were included. Investigation of heterogeneity was presented in a narrative summary.

Applicability/external validity:

The authors note that the majority of studies in this review included adult participants of all ages with many subtypes of glaucoma, and are generalizable to adult participants who undergo glaucoma surgery in the real world. One issue with the overall applicability of this review is that a large variety of interventions were analyzed, with very few studies that analyzed the same intervention that were amenable to meta-analysis.

Geographic focus:

The authors included studies conducted from all income settings, however, they did not discuss applicability of findings to low- and middle-income countries.

Summary of quality assessment:

Overall, there is high confidence in the conclusions about the effects of this study. The authors used comprehensive search methods avoiding biases. In addition, they used rigorous methods to screen studies for inclusion in the review, extract data of included studies and assess risk of bias.