EyeWorld India March 2018 Issue

52 EWAP DEVICES March 2018 by Swarup Swaminathan, MD, Stephen Moster, MD, Nimesh Patel, MD, Nicolas Yannuzzi, MD, Eric Duerr, MD, Ann Quan, MD, Nathan Scott, MD, MPP Review of ‘Trabecular micro-bypass stents as minimally invasive approach after conventional glaucoma filtration surgery’ T he surgical options for managing glaucoma have increased exponen- tially in recent years. Microinvasive glaucoma surgery (MIGS) is a group of procedures characterized by an ab interno approach, minimal trauma to ocular tissue, rapid postoperative recovery, excellent safety profile, and modest efficacy. 1 Current approaches include increasing trabecular outflow, suprachoroidal shunts, reducing aqueous produc- tion (endocyclophotocoagulation), and subconjunctival filtration. 2 MIGS are considered lower risk pro- cedures than traditional incisional glaucoma surgeries (i.e., trabeculec- tomy and tube shunts), which have significantly higher rates of sight-threatening complications such as suprachoroidal hemorrhage and endophthalmitis. 3 Despite the risk profile, traditional glaucoma surgery is still considered the gold standard in patients with advanced and progressive glaucoma. 4,5 The iStent trabecular micro-by- pass stent (Glaukos, San Clemente, California) was the first trabecular stent approved by the U.S. Food and Drug Administration. The iSt- ent is a 1 mm heparin-coated, non- ferromagnetic titanium stent that allows aqueous humor to bypass the trabecular meshwork and drain directly into Schlemm’s canal. 6 The iStent Study Group conducted a multicenter randomized clinical trial evaluating the safety and effi- cacy of iStent placement in combi- nation with phacoemulsification in patients with mild to moderate open angle glaucoma. 7 A greater proportion of patients who under- went phacoemulsification with an iStent achieved an unmedicated IOP ≤ 21 mmHg than phacoemul- sification alone after 1 year of follow-up. However, a significant reduction in IOP was observed in patients receiving only phacoemul- sification. Implantation of multiple stents appears to provide addi- tional IOP reduction compared to placement of a single stent. 8 Macher et al. performed a retrospective study evaluating the outcomes of two trabecular micro- bypass stents in patients with uncontrolled open angle glaucoma and previous filtration surgery. The study included patients with primary open angle glaucoma, pseudoexfoliation glaucoma, and pigmentary glaucoma. All patients required additional IOP lowering while using at least two IOP- lowering drops for greater than 6 months after at least one prior filtration surgery. An open angle was required on gonioscopy. The surgical procedure included inject- ing two iStents utilizing a tempo- ral corneal wound. Of note, the new iStent inject devices (G2-M-IS injector) were utilized, as per the procedure previously described in the literature. 9 In the postoperative period, all patients were placed on topical timolol and pilocarpine for 2 weeks only to prevent synechiae. In this study, 11 eyes (26%) were phakic and underwent con- current cataract removal while the remaining 33 (74%) were pseu- dophakic. At 12 months postop- eratively among patients who had only one previous failed filtration surgery, IOP was reduced from 23.8±3.9 to 15.2±2.7 mmHg. At 12 months among those with mul- tiple prior failed filtration surger- ies, IOP decreased from 26.1±5.7 to 16.3±3.3 mmHg. There was also a reduction in the number of medications used, from 2.7±0.9 to 2.0±1.1. Notably, 15 eyes (36%) required a secondary glaucoma procedure within 6 months after the described intervention. The authors utilized an iStent place- ment grading system to gauge stent positioning, which has not been completed in prior studies and has not been standardized. A total of three eyes (7%) had a post-tra- becular position of the stent, and only one implant was visible after surgery in two eyes (5%). This study challenges our current approach to the surgical management of glaucoma. MIGS has been generally reserved for early stages of glaucoma, poten- tially bridging the gap between laser trabeculoplasty and tradi- tional glaucoma surgery. Use of MIGS in patients with advanced glaucoma has been limited to date. These devices are being implanted with increasing frequency prior to trabeculectomy, but they have not typically been considered in eyes that have already undergone trabeculectomy surgery with subse- quent failure. This study raises the question of whether our standard algorithm for glaucoma surgical treatment should be revised. While the results are intrigu- ing, there are several limitations to the study. The sample size is rela- tively small, and the short follow- up period of 12 months restricts the extent of conclusions that can be drawn. As would be expected with any glaucoma surgery, length of efficacy is essential to assessing its value; we would hope that the IOP-lowering effects of the dis- cussed intervention are longstand- ing, but this is unknown with the current data. Presentation of results using prospectively defined success and failure criteria would be helpful, as has been advocated by the World Glaucoma Associa- tion in its Guidelines on Design and Reporting of Glaucoma Surgical Tri- als . 10 Such definitions would allow for a rudimentary survival analysis, albeit the follow-up period of this study is relatively short. Two distinct cohorts are