Retrobulbar tube shunt: anterior chamber to back of the eye (A2B) efficacy in glaucomatous eyes with uncontrolled IOP

Purpose: The purpose of this study is to examine the efficacy and safety of a commercial model of the retrobulbar shunt, anterior chamber to back of the eye (A2B), in lowering intraocular pressure (IOP) and medication requirements after the failure of all other IOP-lowering therapies, including trabeculectomy with antimetabolites and tube shunt procedures. Methods: This is a single-site, prospective, nonrandomized concept study. Patients with prior failed tube shunts, or moderate to severe glaucoma refractory to treatment, were included. All subjects underwent A2B shunt implantation. Each subject’s IOP and number of medications were assessed from baseline at each time interval using paired t tests. Primary outcome measures were IOP and glaucoma medication use pre- and postoperatively. Complete success is defined as (1) IOP ≤ 21 mmHg; (2) IOP reduction from baseline of ≥ 20%; (3) no reoperation for glaucoma; (4) no loss of light perception vision; (5) no chronic hypotony defined as IOP ≤ 5 mmHg; and (6) no use of supplemental glaucoma medication. “Qualified success” required satisfaction of the same criteria as “complete success” but with the use of supplemental glaucoma medication at 6 months. Results: Nineteen eyes of 19 patients (mean age 39.5 ± 6.4) were followed for 6 months. The mean IOP (mmHg±SEM) at 6 months dropped from baseline of 35.3 ± 2.3 to 18.5 ± 1.1(− 16.8, − 47%; p < 0.0001). The mean number of glaucoma medications (±SEM) at 30, 90, and 180 days decreased from a baseline of 2.4 ± 0.3 to < 0.3 at each interval (p < 0.0002). The complete and qualified success rates at 6 months were 46.6% (7/15) and 66.6% (11/15), respectively. The mean number of prior incisional glaucoma surgeries was 3.2. The percent of patients that had previously failed sub-Tenon tube shunt surgeries was 79%. Conclusions: The A2B shunt is an effective rescue therapy in patients that have failed other IOP-lowering procedures. By shunting aqueous humor into the retrobulbar space, IOP and number of glaucoma medications required were substantially reduced for the 6-month postoperative assessment interval. The intrinsic properties of the retrobulbar space may limit the risk of fibrosis, the principal cause of bleb failure.