Ab externo Schlemm’s canal surgery: Efficacy and safety outcomes

The purpose of this article is to review the existing literature on the efficacy and safety of ab externo viscocanalostomy (VCS) and canaloplasty (CP) in glaucoma patients. A literature search was conducted, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 Statement Criteria, in Medline (via PubMed), Embase (Ovid), Web of Science (Clarivate Analytics) and Cochrane Library (Cochrane). Wherever possible, level of evidence has been assessed by means of the oxford center for evidence-based medicine level of evidence classification. Twenty-nine articles were included providing data for 2790 subjects. The mean preoperative medicated intraocular pressure (IOP) was 25.06 ± 5.29 mmHg in the CP group and 36.22 ± 11.20 mmHg in the VCS group. The mean postoperative IOP was 14.98 ± 1.28 mmHg in the CP group and 15.17 ± 1.34 mmHg in the VCS group at 36 months of follow-up. CP and VCS showed a mean IOP reduction from baseline of 40.21% and 58.12%, respectively, and medication reduction of 72.37% and 81.01%, respectively, after 36 months of follow-up. Perforation of the trabeculo-descemetic membrane was reported in 5.39% (CP group) and in 8.24% (VCS group) of cases (micro) hyphema was the most reported postoperative complication. CP and VCS significantly reduce IOP and medication use. The incidence of complications seen in filtration surgery is minimized by these nonpenetrating and bleb-independent approaches. With its efficacy and high safety profile, Schlemm's canal surgery is a valuable alternative to penetrating glaucoma filtration surgery.