Micro-invasive glaucoma surgery (MIGS): a review of surgical procedures using stents

Abstract

Over the last decade several novel surgical treatment options and devices for glaucoma have been developed. All these developments aim to cause as little trauma as possible to the eye, to safely, effectively, and sustainably reduce intraocular pressure (IOP), to produce reproducible results, and to be easy to adopt. The term "micro-invasive glaucoma surgery (MIGS)" was used for summarizing all these procedures. Currently MIGS is gaining more and more interest and popularity. The possible reduction of the number of glaucoma medications, the ab interno approach without damaging the conjunctival tissue, and the probably safer procedures compared to incisional surgical methods may explain the increased interest in MIGS. The use of glaucoma drainage implants for lowering IOP in difficult-to-treat patients has been established for a long time, however, a variety of new glaucoma micro-stents are being manufactured by using various materials and are available to increase aqueous outflow via different pathways. This review summarizes published results of randomized clinical studies and extensive case report series on these devices, including Schlemm's canal stents (iStent^®, iStent^® inject, Hydrus), suprachoroidal stents (CyPass^®, iStent^® Supra), and subconjunctival stents (XEN). The article summarizes the findings of published material on efficacy and safety for each of these approaches.

Keywords: CyPass; Hydrus; MIGS; XEN; glaucoma; iStent; iStent inject; micro-invasive glaucoma surgery.

Figure 1

iStent^® and iStent^® inject. Notes: The first generation iStent (A) has a self-trephining tip which is inserted into Schlemm’s canal. The device is maintained by the three retention arches. The lumen is directed toward the anterior chamber. (B) iStent inject possesses four side holes opening toward Schlemm’s canal. The central lumen is directed toward the anterior chamber. Abbreviation: AH, aqueous humour.

Figure 2

Development of mean IOP after the implantation of iStent^® during combined procedures (implantation with phacoemulsification and IOL implantation). Notes: Reduction of mean intraocular pressure compared to medicated and/or unmedicated baseline visit. In the study of Belovay et al the results were reported separately for patients with the implantation of two or three iStents (*one iStent, **two iStents implanted). In the study by Patel et al no standard deviations were given. Numbers on the horizontal axis indicate the month of visit. Abbreviations: IOP, intraocular pressure; IOL, intraocular lens; BM, medicated baseline IOP; BU, unmedicated baseline IOP; U, unmedicated; M, medicated.

Figure 3

Development of mean IOP after the implantation of iStent^® during stand alone procedures. Notes: Reduction of mean intraocular pressure at last visit compared to medicated and/or unmedicated baseline visit. In the study of Katz et al the results were reported separately for patients with the implantation of one, two or three iStents. In the study of Ahmed et al IOP lowering medication (travoprost) was re-established at month 13. Month 18 represents the IOP data including travoprost as a medical therapy. Numbers on the horizontal axis indicate the month of visit. Abbreviations: IOP, intraocular pressure; BM, medicated baseline IOP; BU, unmedicated baseline IOP; U, unmedicated; M, medicated.

Figure 4

Development of mean IOP after the implantation of iStent inject^® during stand alone procedures. Notes: Reduction of mean intraocular pressure at last visit compared to medicated and/or unmedicated baseline visit. iStent inject was implanted in all studies as a stand-alone procedure. In the study of Klamann et al the results were reported separately for patients with POAG and PEX. Numbers on the horizontal axis indicate the month of visit. Abbreviations: IOP, intraocular pressure; POAG, primary open-angle glaucoma; PEX, exfoliative glaucoma; BM, medicated baseline IOP; BU, unmedicated baseline IOP; U, unmedicated; M, medicated.

Figure 5

The Hydrus^® micro-stent.

Figure 6

The CyPass^® micro-stent placed on a guidewire.

Figure 7

Mean IOP ± SD at baseline and 12 months after the implantation of CyPass. Notes: In the studies of Hoeh et al and Vold et al the implantation of CyPass was performed as a combined procedure during a cataract extraction with phacoemulsification and the implantation of an intraocular lens. In the study of García-Feijoo et al CyPass was implanted in a stand-alone procedure in phakic and pseudophakic eyes. Numbers on horizontal axis indicate the month of visit. Abbreviations: IOP, intraocular pressure; BM, medicated baseline IOP; BU, unmedicated baseline IOP; M, medicated; U, unmedicated.