Editors Selection IGR 21-2

Surgical Treatment: Ab externo microshunt

Steve Mansberger

Comment by Steve Mansberger on:

86439 Intermediate Outcomes of a Novel Standalone Ab Externo SIBS Microshunt With Mitomycin C, Schlenker MB; Durr GM; Michaelov E et al., American Journal of Ophthalmology, 2020; 215: 141-153

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Clinicians have many surgical options for lowering IOP. While trabeculectomy and glaucoma tube shunts are a mainstay of surgical treatment of glaucoma, glaucoma patients would benefit from surgeries that have a short learning curve, excellent efficacy, and low risk of complications. The Preserflo MicroShunt (Santen, Miami, Florida, USA) may be a new option for these goals. It incorporates a commonly-used, biocompatible, synthetic polymer known as SIBS to create a filtering bleb through an ab externo approach at the limbus.

Schlenker et al. use a retrospective case series to investigate the efficacy and risk factors for failure of the Preserflo MicroShunt with MMC in a large cohort (N = 164) of open-angle glaucoma (OAG) patients with an IOP above target and/or progressing on maximally tolerated medical therapy and that had at least one year of follow-up. Surgical technique was the same in all eyes but the concentrations of MMC varied in the study: 31% of patients received 0.2 mg/mL, 56% received 0.4 mg/mL, and 13% received 0.5 mg/mL. Median IOP decreased from 20 mmHg (range, 16.5-26mmHg) to 12 mmHg (range, 10-15mmHg). The paper seems to suggest that the number of glaucoma medication decreased from a median of 4.0 (range 3-4) to 0 postoperatively with a range of (0-0). However, the range should incorporate more than 0, and this may be a typographical error.

Complete success (defined as an IOP of 6 to 17 mmHg and at least a 20% IOP reduction) at one year was achieved in 76.9% of cases, and qualified success (with medications) was 91.8%. Lower concentrations of MMC (0.2 mg/mL) and primary open angle glaucoma diagnosis were associated with a higher risk of failure (hazard ratio, 2.51; 95% CI, 1.12-5.65 and 2.51; 95% CI 1.01-6.23, respectively). Table 2 suggests that 8.5% of eyes required needling and 3% required anterior chamber reformation. Other complications are similar to trabeculectomy and glaucoma tube placement with 6.7% with choroidal detachment and 5.5% with shallow anterior chamber. However, the rate of postoperative complications is lower than those reported in a recent trabeculectomy and glaucoma tube placement study.1 The authors highlight that patients may require a higher dose of mitomycin C (≥ 0.4mg/ml) for improved success.

The authors should be congratulated on providing the results of Preserflo MicroShunt on a large cohort of patients with glaucoma. The study had a small proportion lost to follow-up, rigorous outcome measures, and detailed analysis. This surgery requires some of the same skills as trabeculectomy and glaucoma tube surgery including conjunctival incision, placement of mitomycin-C, scleral tunnel creation, and insertion of the shunt with the scleral tunnel track. However, the presumed benefits of this new device is a more standardized surgery with a posterior filtering bleb when compared to standard trabeculectomy, less postoperative visits, and less postoperative interventions. The study is retrospective and non-comparative, but may suggest high potential as a useful device in the surgical treatment of patients with glaucoma.


  1. Gedde SJ, Feuer WJ, Shi W, et al; Primary Tube Versus Trabeculectomy Study Group. Treatment Outcomes in the Primary Tube Versus Trabeculectomy Study after 1 Year of Follow-up. Ophthalmology. 2018;125(5):650-663. doi: 10.1016/j. ophtha.2018.02.003. Epub 2018 Feb 21. PMID: 29477688.

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