Ab Externo SIBS Microshunt with Mitomycin C for Open-Angle Glaucoma: Three-Year Results as a Primary Surgical Intervention

Abstract

Purpose: To determine the effectiveness, risk factors for surgical failure, and adverse events in a large cohort of patients receiving stand-alone ab externo poly(styrene-block-isobutylene-block-styrene) (SIBS) microshunt implantation with mitomycin C (MMC) over 3 years of follow-up.

Design: Retrospective, interventional case series.

Participants: Glaucomatous eyes on maximally tolerated medical therapy with no previous subconjunctival glaucoma surgery.

Methods: Records of eyes that underwent ab externo SIBS microshunt with MMC between July 2015 and November 2017 were reviewed. Data from all follow-up visits were utilized and included intraocular pressure (IOP), medication use, postoperative interventions, complications, and reoperations.

Main outcome measures: The primary outcome was proportion of eyes at 3 years with (1) no 2 consecutive IOPs > 17 mmHg (or < 6 mmHg with > 2 lines of vision loss from baseline); (2) ≥ 20% reduction from baseline IOP; and (3) using no glaucoma medications (complete success). Secondary outcomes included 14 and 21 mmHg upper IOP thresholds with and without ≥ 20% IOP reduction from baseline, qualified success (with glaucoma medications), risk factors for failure, median IOP/medications, postoperative interventions, complications, and reoperations.

Results: One hundred fifty-two eyes from 135 patients were included. Complete and qualified success was achieved in 55.6% and 74.8% of eyes, respectively. Time to first glaucoma medication use was a median of 16.9 (interquartile range [IQR], 12.1-34.1) months; however, 59.4% of eyes remained medication free at 3 years. Significant risk factors for failure included receiving < 0.4 mg/ml of MMC (adjusted hazard ratio [HR], 2.42; 95% confidence interval [CI], 1.44-4.05) and baseline IOP < 21 mmHg (adjusted HR, 1.79; 95% CI, 1.03-3.13). The most common complications were choroidal detachment, hyphema, and anterior chamber shallowing, occurring in 7%, 5%, and 5% of eyes, respectively. The needling rate was 15.1%, with significantly higher frequency for baseline IOP > 21 mmHg (HR, 3.21; 95% CI, 1.38-7.48). Revisions occurred in 7% of eyes and reoperations in 2.6%. Eyes receiving < 0.4 mg/ml of MMC underwent more revisions (odds ratio, 4.9; 95% CI, 1.3-18.3).

Conclusions: Three-year follow-up data from this large cohort continues to support promising rates of qualified and complete success, with decreased medication burden postoperatively and few postoperative complications and interventions. Comparisons to other filtering surgeries will further facilitate integration of the SIBS microshunt into the surgical treatment paradigm.

Financial disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Keywords: Glaucoma surgery; Microshunt; SIBS; Subconjunctival filtering; Trabeculectomy.