Ab Externo Shunt Procedure Finds a Niche Between MIGS and Trabeculectomy

Microinvasive bleb-forming surgery merges safety of MIGS with better efficacy. Cheryl Guttman Krader reports

The PRESERFLO™ MicroShunt (Santen) is not a replacement for trabeculectomy, but it might be a real game-changer in the realm of glaucoma surgery and a good fit for many patients and surgeons, according to Joseph F Panarelli MD.

“I believe that at least initially, the MicroShunt will bridge a substantial gap between patients who could have microinvasive canal-based surgery and those who need traditional trabeculectomy. The IOP-lowering outcomes may be better with trabeculectomy, but I think they will be more reproducible with the MicroShunt and will improve with refinements to the surgical technique and postoperative management. Therefore, the MicroShunt might be a nice procedure to learn for surgeons who want efficacy-like outcomes of trabeculectomies but do not perform a large volume of those procedures,” he said.

Dr Panarelli also highlighted the postoperative stability and recovery after MicroShunt surgery.

“Often these patients are very happy because they regain visual acuity much more quickly than after trabeculectomy, and they have a much smoother postoperative course. I think when surgeons start performing this procedure, they will see other nuances that will make them want to do it more and more.”

EFFICACY AND SAFETY OUTCOMES Implanted in an ab externo procedure, the MicroShunt drains aqueous humour from the anterior chamber to the subconjunctival/sub-Tenon’s space in a regulated manner. Dr Panarelli described the procedure as microinvasive blebforming surgery.

He reviewed results from two years of follow-up in the pivotal international trial that randomised 891 patients 3:1 to the MicroShunt or trabeculectomy. Eligible patients had primary open-angle glaucoma with uncontrolled IOP 15 to 40 mmHg on maximum tolerated glaucoma medication. Dr Panarelli highlighted two characteristics of the study population.

“About one-third of patients had a preoperative IOP <18 mmHg, and that is a tough group for getting a low final IOP. In addition, an appreciable subset of patients (about 15%) had severe glaucoma. These are patients who need very substantial IOP-lowering,” he said.

Surgical success, defined by a ≥20% reduction in diurnal IOP without increasing medications, was achieved in 64% of patients randomised to trabeculectomy and 51% of those in the MicroShunt group. Mean IOP was 21 mmHg at baseline in both groups and s was 13.9 mmHg in the MicroShunt group and 10.7 mmHg in the trabeculectomy group. The average daily number of medications for the trabeculectomy and MicroShunt groups was 0.9 and 0.4, respectively.

“Keep in mind this was a really experienced group of trabeculectomy surgeons who participated in the study, but I think the MicroShunt did quite well for a new procedure,” Dr Panarelli said.

There were few serious postoperative complications in either group. Adverse event rates were generally similar between groups other than hypotony. Persistent hypotony and early bleb leaks were more common after trabeculectomy. Notably, rates of cataract progression, corneal oedema, hypotony maculopathy, and change in endothelial cell density were similar in the two groups. Rates of bleb needling, introduction of glaucoma medications, reoperations, and other glaucoma surgeries were all higher in the MicroShunt group.

“Often these patients are very happy because they regain visual acuity much more quickly than after trabeculectomy, and they have a much smoother postoperative course.”

The study was presented at AAO 2021 in New Orleans, Louisiana, USA.

Joseph F Panarelli MD is the Chief, Division of Glaucoma Services, New York University Grossman School of Medicine, USA. joepanarelli@gmail.com