Methodological quality of the review: Medium confidence

Author: Minckler D, Vedula SS, Li T, Mathew M, Ayyala R, Francis B

Geographical coverage: Not reported

Sector: Glaucoma

Sub-sector: Shunts/drainage devices

Equity focus: None specified

Review type: Meta-analysis

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: Glaucoma is a leading cause of blindness worldwide with types of treatment ranging from eye drops to laser treatment and surgical operations.

Where eye drops and lasers are deemed ineffective as treatment options, surgery is performed. From the different types of surgical procedures, aqueous shunts (glaucoma drainage devices) are often used in convoluted cases where modes of surgery such as trabeculectomy (Trab) have not worked.

The structure of a typical aqueous shunt includes a small rubber tube (drain) which connects the eye fluid chamber to a plate that is attached to the eye wall. The plate, or explant, accommodates a space into which eye fluid can drain. The review herein attempts to summarise previously published, randomised and quasi-randomised controlled trial results for aqueous shunts (studies that compare treatment with no treatment or to alternative treatments including a control group).

The review focuses on 15 trials involving 1153 participants with varied diagnoses of glaucoma. The findings suggest there is insufficient evidence to conclude that clinical outcomes of Trab do not differ substantially from those of aqueous shunts in similar patients with complicated glaucoma. Furthermore, the authors acknowledge the lack of evidence to conclude that any specific aqueous shunt is superior to others currently in widespread use.

Objectives: This review compares the safety and effectiveness of different aqueous shunts for reducing IOP in glaucoma.

Main findings: Fifteen studies were included in this review, which used a range of measures that were clinically relevant. The thematic focus of this study was to compare different aqueous shunts for reducing IOP in glaucoma. The present study established that there are too few published randomised studies on aqueous shunts, and that methodology and data quality among them is poor. As a result, there was no evidence of superiority of one shunt over another.

Based on this review, no particular shunt stands out as clinically superior with regard to safety or efficacy. It is suggested that practitioners select their device of choice based on their own experience, and use shunts they are most comfortable with.

Authors recommend the organisation of additional trials to compare devices with regards to issues of safety as well as the immediate risk of post-operative hypotony and its complications. They also go on to suggest the use of more standardised definitions and terminology for the types of glaucoma and its complications. Data collection and intervals must also be standardised with a continued follow-up of several years. Planning future studies of aqueous shunts in complex glaucoma should include pre-study planning to allow for the recruitment of adequate sample sizes in each disease type, in order to answer certain study questions.

Methodology: The authors selected trials that were only randomised or quasi-randomised, searching an appropriate time period. The participants included were limited to those diagnosed with glaucoma, and no significant restrictions were placed on the types of participants.  The list of trials included were based on studies that compared shunts with standard surgery procedures, as well as trials investigating different types of shunts.

The primary outcomes focused on controlling IOP, while the secondary outcomes of the review were visual acuity, duration of post-operative hypertensive phase, follow-up intervals and visual field progress. The different complications were tabulated, mainly focusing on post-operative issues. The data on quality of life available from the included studies was also listed and summarised.

The authors identified trials from the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library, MEDLINE (PubMed), EMBASE and Latin American and Caribbean Health Sciences Literature Database (LILACS). The updated searches included the National Research Register (NRR) database. There were no language or date restrictions placed on the electronic searches. Reference lists were searched to further identify trial reports. The Science Citation Index, conference proceedings or abstracts were not specifically searched for this review.

Two authors independently assessed the titles and abstracts of all reports identified by the electronic and manual searches, and a third author resolved the differences. Primary investigators were contacted and studies were excluded upon agreement by both independent authors. Where data was missing, primary investigators were again contacted. IOP data was extracted from the published papers, and the mean IOP values calculated where mean change in IOP was not available. Where success in controlling IOP was analysed using Kaplan-Meier or life-table analyses, the authors tried to extract data on log-hazard ratios either through log-rank statistics or through published Kaplan-Meier curves.

For dichotomous outcomes, the authors calculated a summary risk ratio. In turn, the mean differences for continuous outcomes – including mean post-operative IOP, logMAR visual acuity and anti-glaucoma medications – were all assessed. Statistical heterogeneity was tested for using the chi-square test and by examining the I² value. A fixed-effect model was employed where there were fewer than three trials in the analyses. In cases of statistical or clinical heterogeneity, the authors did not combine study results but presented a narrative summary. No sub-group analysis was performed, and sensitivity analyses were also excluded due to a lack of included studies being funded by industry.

Applicability/external validity: The authors discussed the inconclusive nature of this review and advised the need for a more standardised study design and plan.

Geographic focus: The authors failed to highlight or mention the geographical focus of the review.

Publication source: Minckler D, Vedula SS, Li T, Mathew M, Ayyala R, Francis B. Aqueous shunts for glaucoma, Cochrane Database of Systematic Reviews 2006, 2.

Summary of quality assessment: Overall, high quality was attributed in the conclusions about the effects of this study. Authors used appropriate methods to identify and extract data, and appraise included studies. In addition, methods used to analyse findings were clear. The limitations of the paper were acknowledged with further long-term research required to test for parity between shunts.