Abstract: The review included six trials with a total of 361 participants. Two studies were conducted in America and one each in Germany, Greece, India, and Saudi Arabia. The participants of four trials had open-angle glaucoma; one study included participants with primary open-angle or primary closed-angle glaucoma, and one study did not specify the type of glaucoma. Three studies used a combined procedure (phacotrabeculectomy). Trabeculectomy with mitomycin C (MMC) was performed in four studies, and trabeculectomy with 5-fluorouracil (5-FU) was performed in only one study. None of the included trials reported trabeculectomy failure at 24 months. Only one trial reported the failure rate of trabeculectomy as a late complication. Failure was higher among participants randomised to the limbal-based surgery: 1/50 eyes failed trabeculectomy in the fornix group compared with 3/50 in the limbal group (risk ratio (RR) 0.33, 95% confidence interval (95% CI) 0.04 to 3.10); therefore we are very uncertain as to the relative effect of the two procedures on failure rate. Four studies including 252 participants provided measures of mean IOP at 12 months. In the fornix-based surgeries, mean IOP ranged from 12.5 to 15.5 mmHg and similar results were noted in limbal-based surgeries with mean IOP ranging from 11.7 to 15.1 mmHg without significant difference. Mean difference was 0.44 mmHg (95% CI −0.45 to 1.33) and 0.86 mmHg, (95% CI −0.52 to 2.24) at 12 and 24 months of follow-up, respectively. Neither of these pooled analyses showed a statistically significant difference in IOP between groups (moderate quality of evidence). One trial reported number of anti-glaucoma medications at 24 months of follow-up with no difference noted between surgical groups. However, three trials reported the mean number of anti-glaucoma medications at 12 months of follow-up without significant difference in the mean number of postoperative IOP-lowering medications between the two surgical techniques. Mean difference was 0.02, (95% CI −0.15 to 0.19) at 12 months of follow-up (high quality of evidence). Because of the small numbers of events and total participants, the risk of many reported adverse events were uncertain and those that were found to be statistically significant may have been due to chance. For risk of bias assessment: although all six trials were randomised selection bias was mostly unclear, with unclear random sequence generation in four of the six studies and unclear allocation concealment in five of the six studies. Attrition bias was encountered in only one trial which also suffered from reporting bias. All other trials had an unclear risk of reporting bias as there was no access to study protocols. All included trials were judged to have high risk of detection bias due to lack of masking of the outcomes. Trabeculectomy is quite a standard procedure and unlikely to induce bias due to surgeon 'performance', hence performance bias was not evaluated. The main result of this review was that there was uncertainty as to the difference between fornix- and limbal-based trabeculectomy surgeries due to the small number of events and confidence intervals that cross the null. This also applied to postoperative complications, but without any impact on long-term failure rate between the two surgical techniques.

Plain-language summary: Six randomised controlled trials (RCTs) were reviewed with a total of 361 participants consisting of adults with any type of glaucoma and follow-up of at least 24 months. We last searched the databases on 23 October 2015. Failure rate at 24 months was not reported in any included studies, and one study reported "late complications" but did not specify a time period, which favoured the fornix-based treatment. No difference was noted with respect to lowering eye pressure after 24 months (two trials) and after 12 months (four trials). The number of medications needed to control eye pressure after surgery was also similar. Moreover, most of the studies reported that the complication rates after the operation were similar except in one complication which was narrowing in the anterior part of the eye after the procedure (more common in the limbal surgery group), but this did not affect the final outcome of the surgery. Although all six trials were reported to be randomised, the procedures followed for randomisation were mostly unclear (four of the six studies). Masking of the outcomes was not clear or not addressed in all six trials. Missing information was encountered in only one trial which also suffered from bias in reporting its outcomes. All other trials had an unclear risk of reporting bias as there was no access to original data.