Determine the efficacy of stand-alone implantation of the ab externo SIBS or poly(styrene-block-isobutylene-block-styrene) microshunt with mitomycin C in glaucomatous eyes, refractory to previous subconjunctival filtering surgery, over 1 year of follow-up.
Consecutive retrospective cohort of patients with intraocular pressure (IOP) above target and previous subconjunctival filtering surgery, who received the microshunt between July 2015 and April 2019. Primary outcome was a complete success, with failure defined as IOP 17 mm Hg or <20% reduction in IOP without medications. Secondary outcomes included thresholds of 6 to 14 mm Hg and 6 to 21 mm Hg for both complete (no medications) and qualified (with medications) success as well as qualified success for thresholds of 6 to 17 mm Hg. Risk factors for failure, IOP, medications and complications were also assessed.
85 eyes of 79 patients with a preoperative median IOP of 22.0 mm Hg (IQR 18.0-29.0) on four (IQR 3-4) medications were included. Postoperative median IOP was 13.0 mm Hg (IQR 10.0-17.0) on zero (IQR 0-2) medication at 1 year. 61.0% achieved complete success and 79.7% achieved qualified success. Mild-to-moderate disease was associated with failure (adjusted HR 2.37; 95% CI 1.23 to 4.59). Needling was performed in 11.8%, and 8.2% underwent anterior chamber reformation. Complications were transient, consisting of hyphaema, choroidal detachment and hypotony maculopathy, with 7.1% of patients undergoing reoperation.
In a group of high-risk eyes that had already failed at least one subconjunctival filtering surgery, the SIBS microshunt demonstrates reasonable surgical success over 1-year follow-up, with relatively few complications.

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