Ab interno trabecular bypass surgery with istent for open‑angle glaucoma

Author: Le JT, Bicket AK, Wang L, Li T.

Geographical coverage: Armenia, Italy, Spain, the United States of America (USA), Germany and the United Kingdom (UK).

Sector: Glaucoma treatment

Sub‑sector: Treatment

Equity focus: Not reported

Study population: Patients with open‑angle glaucoma (OAG)

Review type: Effectiveness review

Quantitative synthesis method: Narrative synthesis and meta‑analysis

Qualitative synthesis method: Not applicable

Background

Glaucoma is a leading cause of irreversible blindness worldwide. In its early stages the condition is asymptomatic, gradually progressing to visual impairment and eventually blindness. Elevated intra‑ocular pressure (IOP) is the only modifiable risk factor. Minimally invasive glaucoma surgery (MIGS)—such as ab interno trabecular bypass surgery with the istent micro‑stent—has emerged as a treatment option, but its ability to eliminate the need for topical IOP‑lowering medication and to deliver other benefits remains uncertain.

Objectives

To evaluate the effectiveness and safety of ab interno trabecular bypass surgery with the istent (or istent inject) for OAG compared with conventional medical, laser or surgical treatment.

Main findings:

Treatment with the istent may increase the proportion of participants who are drop‑free and may improve IOP control at short‑, medium‑ and long‑term follow‑up.

A total of 362 records were identified; seven randomised controlled trials (RCTs) (19 reports, 764 participants) met the inclusion criteria for the narrative synthesis and two contributed data to the meta‑analysis. The trials were conducted in Armenia, Italy, Spain, the United States of America (USA), Germany and the United Kingdom (UK). Sample sizes ranged from 33 to 239 participants. The majority of participants were women (417; 55 %) and older adults (49–89 years). All seven trials were sponsored by Glaukos Corporation, which manufactured the device, and the certainty of evidence was therefore graded as very low.

Four RCTs evaluated the istent combined with phaco‑emulsification compared with phaco‑emulsification alone. A pooled analysis of two trials showed that the combined procedure increased the likelihood of being drop‑free at 6–18 months post‑operatively (risk ratio 1.38, 95 % confidence interval 1.18–1.63; I² = 67 %). Two trials also reported a modest reduction in the number of IOP‑lowering drops required (mean difference −0.42 drops, 95 % confidence interval −0.60 to −0.23). Evidence for mean IOP reduction from baseline remained inconclusive because no meta‑analysis was possible.

Two RCTs compared the istent with standard medical therapy; one evaluated the istent inject. Clinical and methodological heterogeneity precluded pooling, but each trial reported that more than 90 % of participants in the istent groups were drop‑free at 6–18 months, whereas none in the medical‑therapy groups achieved this outcome.

One RCT compared the implantation of one, two or three istents. Up to 36 months there was no difference in the proportion of drop‑free participants, but at 42 months those who received a single istent were less likely to be drop‑free than those who received two (risk ratio 0.51, 95 % confidence interval 0.34–0.75) or three (risk ratio 0.49, 95 % confidence interval 0.34–0.73) devices. The study did not report the change in the mean number of IOP‑lowering drops.

The type and timing of complications varied across trials. Similar proportions of participants required secondary glaucoma surgery after combined istent‑plus‑phaco‑emulsification and phaco‑emulsification alone. None of the trials reported health‑related quality‑of‑life outcomes.

Methodology:

Searches of MEDLINE, Embase, the Cochrane Central Register of Controlled Trials (CENTRAL), ClinicalTrials.gov, the World Health Organization International Clinical Trials Registry Platform (ICTRP), the ISRCTN registry and the US Food and Drug Administration (FDA) website were undertaken on 17 August 2018 without language or date restrictions. Reference lists of included studies and manufacturers’ websites were also screened. Two reviewers independently screened records, extracted data and assessed risk of bias following Cochrane guidance. Fixed‑effect meta‑analysis was used where appropriate; heterogeneity was explored with the I² statistic and publication bias with funnel plots.

Applicability/external validity:

Generalisability is limited by manufacturer funding and largely homogeneous study populations (predominantly older White adults). The lack of quality‑of‑life data and inconsistent reporting of adverse events further restrict applicability to routine clinical practice.

Geographic focus:

The included studies were conducted in Armenia, Italy, Spain, the United States of America (USA), Germany and the United Kingdom (UK).

Summary of quality assessment:

The authors applied rigorous systematic‑review methods, however the certainty of the evidence for key outcomes was very low because all trials were manufacturer‑funded and at risk of bias.