Types of studies

We included randomised controlled trials (RCTs) reported in any language irrespective of their publication status. 

Types of participants

Study participants had OAG of any type, including primary and secondary OAG. Closed angle glaucoma was excluded. As there are no universally‐accepted criteria by which glaucoma may be defined, we permitted studies to use their own definitions of glaucoma (provided these were clearly stated). In addition, participants with ocular hypertension, normal tension glaucoma, or possible glaucoma (suspects for glaucoma) were included. We did not apply any restrictions regarding location, setting, or demographic factors.

Types of interventions

We compared ab interno supraciliary microstent surgery with the Cypass (Alcon Laboratories, a division of Novartis, Basel, Switzerland), iStent Supra (Glaukos Corporation, Laguna Hills, CA, USA) or other supraciliary microstents that were identified during this review to:

• laser treatment (selective laser trabeculoplasty or argon laser trabeculoplasty);

• other minimally‐invasive glaucoma surgery (MIGS) techniques;

• conventional glaucoma surgery (trabeculectomy);

• medical therapy.

RCTs were considered where supraciliary microstent devices were used in combination with phacoemulsification, as well as RCTs where these devices were used in isolation. 

Types of outcome measures

We did not use the reporting of particular outcomes as a criterion for eligibility for review. We did not exclude studies from review solely on the grounds of an outcome of interest not being reported.

We planned to report outcomes in the short‐term (six to 18 months), medium‐term (18 to 36 months), and long‐term (36 months onwards).

Electronic searches

The Cochrane Eyes and Vision Information Specialist searched the following databases for randomised controlled trials and controlled clinical trials. There were no restrictions to language or year of publication. The date of the search was 27 August 2020.

• Cochrane Central Register of Controlled Trials (CENTRAL; 2020, Issue 8) (which contains the Cochrane Eyes and Vision Trials Register) in the Cochrane Library (searched 27 August 2020) (Appendix 1);

• MEDLINE Ovid (1946 to 27 August 2020) (Appendix 2);

• Embase Ovid (1980 to 27 August 2020) (Appendix 3);

• ISRCTN registry (www.isrctn.com/editAdvancedSearch; searched 27 August 2020) (Appendix 4);

• US National Institutes of Health Ongoing Trials Register ClinicalTrials.gov (www.clinicaltrials.gov; searched 27 August 2020) (Appendix 5);

• World Health Organisation (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp; searched 27 August 2020) (Appendix 6).

Searching other resources

We searched the reference lists of included studies for other possible studies. We also searched the websites of the manufacturers of current ab interno supraciliary microstents (Alcon.com, Alcon Laboratories, a division of Novartis, Basel, Switzerland; Glaukos.com, Glaukos Corporation, Laguna Hills, CA, USA) for any information on forthcoming trials.

Selection of studies

Two review authors working independently (AS, HJ) screened titles and abstracts of all articles identified by the search using web‐based online review management software (Covidence). If abstracts were not available, full‐text articles were screened. Two review authors (AS, HJ) independently assessed full‐text reports of all potentially eligible studies. If there was disagreement regarding eligibility, a third review author arbitrated. If any full‐text reports were rejected, the reasons for this were recorded in the Characteristics of excluded studies table.

Data extraction and management

We extracted data from reports of included studies using a data collection form. Two review authors (AS, HJ) worked independently to extract study characteristics from reports and entered the data into Review Manager 5 (RevMan 5) (Review Manager 2020). The same authors extracted the data for analyses, and one review author (AS) checked the data before entering it into Review Manager (RevMan 5). If there was disagreement, a third review author arbitrated.

The process included cross‐checking data entry independently using Covidence to support this. If there was disagreement, a third independent review author would arbitrate.

We presented the data collected in Appendix 7 in the Characteristics of included studies table. Where data on included studies were missing or unclear, we planned to contact the individuals or organisations involved to obtain clarification. We collected and used the most detailed numerical data available to facilitate analyses of included studies. We attempted to obtain these data from individuals or organisations in preference to less precise methods such as extracting numeric data from graphs. If this was necessary, two independent review authors extracted the data and a third review author arbitrated, in case of disagreement.

Assessment of risk of bias in included studies

We used the Cochrane 'Risk of bias' tool as described in Chapter 8 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2017) to assess the risk of bias and assign judgements of this for included studies. Two review authors (AS, HJ) performed this 'Risk of bias' assessment independently. In the event of a disagreement, a third review author was available to arbitrate.

Measures of treatment effect

The primary outcome was the proportion of participants who were medication‐free at the studies' end. We used a risk ratio as the treatment effect measure. In assessing this effect measure, we have reported how prescribing of IOP‐lowering eye‐drops was determined during follow‐up, where this information was available. We examined whether the people measuring IOP and those deciding upon the prescribing of IOP‐lowering eye‐drops were masked to treatment group.

We have also reported mean change in IOP from randomisation to the studies' end. Secondary safety outcomes were to be reported as risk ratios. Health‐related quality of life outcomes were to be reported as differences in means or risk ratios for continuous and binary data, respectively.

Unit of analysis issues

We assessed whether included studies had included one or two eyes from each participant and whether or not randomisation has been conducted at the level of the participant or the eye. There is a potential for medical treatments, such as topical beta blockers used for one eye, to influence the outcome in the other eye (Piltz 2000). Surgery to lower IOP in one eye may also affect the IOP of the fellow eye (Radcliffe 2010). Therefore, we have excluded studies that had adopted a paired eye design. In the event of a multiple arm study being identified, this could be included providing the respective study design was adequate to ensure independent analysis of each treatment group occurred.

Dealing with missing data

We endeavoured to minimise missing outcome data by contacting individuals and organisations to obtain them. If the data were unavailable but the level of missing data in each group and reasons for missing data in each group were similar, we simply analysed available‐case data if an intention‐to‐treat (ITT) analysis had not been performed. We reported if authors had conducted their own ITT analysis despite missing data, but intended to document whether they provided any justification for the method they had used to deal with missing data and whether they had compared their ITT result with an available‐case result.

Assessment of heterogeneity

We intended to assess the heterogeneity between trials by careful examination of the study reports, assessing forest plots and an examination of the I² value, however, as only one RCT met the inclusion criteria of this review, this was not necessary.

Assessment of reporting biases

We planned to use a funnel plot to assess the risk of publication bias if there were more than 10 trials within our review.

Data synthesis

We planned to undertake a meta‐analysis where data appeared clinically, methodologically, and statistically homogeneous. We planned to check that participants, interventions, comparators, and outcomes were sufficiently similar to give a clinically meaningful result and that our I² result did not indicate considerable inconsistency (i.e. I² less than 50%). If all estimates were in the same direction, we would meta‐analyse even where heterogeneity was evident but would comment on this. We planned to use a random‐effects model unless there were fewer than three eligible studies, in which case, we would use a fixed‐effect model. As we found only one study, a fixed‐effects model was used.

Subgroup analysis and investigation of heterogeneity

No subgroup analyses were performed in this review.

Sensitivity analysis

We planned to assess the impact of including studies at high risk of bias for an outcome in one or more key domains. However, there were too few included studies to conduct such analyses. 

Summary of findings and assessment of the certainty of the evidence

We prepared a table to summarise the findings of the review, including the assessment of the certainty of evidence for all outcomes using the GRADE approach (GRADEpro).

We reported the following outcomes at medium‐term follow‐up (18 to 36 months) in the 'Summary of findings' table for each comparison listed in the Types of interventions:  Ab interno supraciliary microstent surgery compared with laser treatment, other MIGS techniques, conventional glaucoma surgery (trabeculectomy), or medical therapy.

• Proportion of participants who were medication‐free (not using eye drops);

• Mean change in IOP, measured using Goldmann applanation tonometry;

• Mean change in number of IOP‐lowering drops taken per day;

• Proportion of participants who required further glaucoma surgery, including laser;

• Rate of visual field progression (decibels (dB)/time) or proportion of participants whose field loss progressed in the follow up period;

• Mean change in health‐related quality of life;

• Proportion of participants experiencing intraoperative and postoperative complications (any time point).