Safety Profile of Minimally Invasive Glaucoma Surgery

Kateki Vinod; Steven J. Gedde


Curr Opin Ophthalmol. 2021;32(2):160-168. 

In This Article


The benefit of any glaucoma procedure in reducing IOP must be considered in the context of its adverse events. An inevitable trade-off exists between safety and efficacy with currently available glaucoma procedures. Although trabeculectomy and tube shunt surgery are very effective at lowering IOP, they are associated with high rates of complications. On the other hand, MIGS offers only modest efficacy but, in most cases, a more favorable safety profile.

Rapid visual recovery is the expectation with trabecular meshwork/Schlemm's canal-based MIGS, especially when performed as an adjunct to cataract surgery, but can be impeded by a myriad of potential intraoperative and postoperative complications. Patient selection and meticulous surgical technique can mitigate many of the risks involved with angle-based MIGS. Preoperative gonioscopy to select patients whose angles are open with well-delineated structures is instrumental to avoiding complications resulting from misidentification of the trabecular meshwork/Schlemm's canal, such as inadvertent cyclodialysis cleft creation. Postoperative hyphema following angle-based MIGS may be mitigated by leaving the IOP higher at the end of surgery, but this strategy risks further damage to the optic nerve. The juxtacanalicular trabecular meshwork and inner wall of Schlemm's canal have been identified as the primary site of impaired aqueous outflow in open-angle glaucoma.[89] Removal of these tissues results in permanent disruption to the blood–aqueous barrier. Delayed-onset hyphema has been reported with angle-based MIGS during periods of elevation in episcleral venous pressure relative to intraocular pressure.

The Xen gel stent is engineered from biocompatible, flexible material with a set length and inner luminal diameter based on the Hagen–Poiseuille equation to minimize hypotony and related sequelae. However, its complication profile is similar to that of traditional glaucoma surgery despite a less invasive surgical technique. Device-related adverse events like migration and erosion resemble those observed with tube shunts, whereas bleb-related complications like fibrosis and overfiltration are analogous to those seen with trabeculectomy. Owing to an inner luminal diameter of only 45 μm, the gel stent may be even more vulnerable to occlusion with microscopic debris than standard tube shunts. Devastating complications like suprachoroidal hemorrhage and endophthalmitis still occur with the gel stent, albeit rarely.

Withdrawal of the CyPass Micro-Stent from the market due to safety concerns stemming from its five-year outcomes reinforced the importance of long-term follow-up. Prospective clinical trials more accurately report rates of adverse events than do retrospective studies, as surgical complications may be overlooked unless attention is specifically directed toward their detection. Additional long-term data are needed to more adequately characterize the safety profile of MIGS and guide the surgical decision-making process.