Eyeworld

EW FEATURE 52 Microinvasive glaucoma surgery (MIGS) • May 2016 AT A GLANCE • MIGS is effective in lowering post- operative complications compared to trabeculectomy by leaving the conjunctiva intact. • Multiple stent placements may allow the surgeon to titrate aqueous flow to suit the needs of the patient. • New stents utilize Schlemm's canal, the subconjunctival space, and the suprachoroidal space to drain aqueous humor and lower IOP. by Stefanie Petrou Binder, MD, EyeWorld Contributing Writer about where we stand and what to expect in microinvasive glaucoma surgery (MIGS). XEN The XEN Gel Stent (Allergan, Dub- lin) is a 6 mm hydrophilic cylindri- cal implant of porcine gelatin that swells when hydrated, adapting to the shape of the surrounding tissue. It is inserted ab interno using a preloaded injector through a clear corneal incision. "We are trying to come up with safer, more effective ways of draining the eye, without the use of trabeculectomy or tube shunts," said Davinder Grover, MD, attending surgeon and clinician, Glaucoma Associates of Texas, Dallas. "The XEN implant does not require conjunctival dissection; it may have a more predictable postoperative course, and appears to control hypo- tony, based on inherent properties of the implant. My goal in glaucoma surgery is to control intraocular pres- sure without side effects like double vision or the potentially lifelong risk of infection of traditional glaucoma surgery." What distinguishes the XEN from other MIGS devices is that it bypasses Schlemm's canal entirely, connecting the anterior chamber with the subconjunctival space. Once implanted, 1 mm of the device stays in the anterior chamber, 3 mm are intrascleral, and the remaining 2 mm of the stent are in the subcon- junctival space. The XEN implant can potentially help a wide spec- trum of glaucoma patients, from mild to moderate to advanced cases, while other stents are more suitable for mild to moderate cases only. "Stents such as the Hydrus [Ivantis, Irvine, California] and the iStent [Glaukos, Laguna Hills, California] open up a segment of the patient's own drainage system," Dr. Grover said. "They will only work if the patient's own drainage system is intact. I would use them for mild or maybe moderate cases of glaucoma to get a modest lowering of pressure or decrease in drops. The XEN is designed to safely and predictably create a new drain, instead of open- ing up the patient's own drainage system, even in very severe glauco- ma cases." In a presentation at the Amer- ican Glaucoma Society annual meeting, Dr. Grover reported on a prospective, non-randomized, inter- national, multicenter case series of the first 975 eyes from more than 45 surgeons who received XEN stents with 3 lumen sizes (140, 63, 45 µm) in patients with mild, moderate, and severe primary open-angle glaucoma (POAG), pigmentary, pseudoexfoli- ative, and refractory glaucomas that were followed for a period of 3 to 36 months. 1 The results at 12 months were promising, revealing an efficacy profile similar to traditional glauco- ma surgery, with far fewer complica- tions, including a 33% drop in IOP and a reduction in anti-glaucoma drops of 1.7. The XEN is part of a Food and Drug Administration (FDA) inves- tigational study in its follow-up phase, with U.S. FDA approval expected in 2016. "The most exciting thing about this technology is that it is an ab interno delivery, appears to be effec- tive, and has a short learning curve. It does not involve an incision in the conjunctiva, which would cause more trauma and scarring and likely induce the surgery to fail. There is immediate IOP reduction and a relatively predictable postoperative course. The small luminal diameter seems to provide enough resistance to aqueous flow to minimize post- operative hypotony. If and when it is approved, the XEN will likely be a great tool in our bag of surgical tricks for safely and effectively man- aging glaucoma," Dr. Grover said. According to Richard Lewis, MD, Sacramento, California, "New concepts and breakthrough tech- nologies take time to be proven safe and effective. Compared to trabe- culectomy, the new MIGS devices have more science behind them in terms of their size, aqueous flow calculations, and the expected level of pressure reduction, but most im- portantly, they are safer." New shunting approaches and ab interno stent placement heighten safety G laucoma researchers are exploring many options in the search for safer and more efficacious ways to shunt aqueous humor out of the anterior chamber to lower IOP. Some devices utilize intact segments of the patient's own drainage system, while others bypass it completely, preferring to shunt aqueous into the subconjunctival or suprachoroidal spaces. These innovative approaches combined with ab interno stent placement are showing much improved and eagerly awaited safety profiles. Here, experienced glaucoma surgeons talk MIGS devices in the pipeline Monthly Pulse Microinvasive glaucoma surgery (MIGS) T he topic of this Monthly Pulse survey was "Microinvasive glaucoma surgery (MIGS)." We asked, "What do you consider the most challeng- ing step in implanting an iStent?" Almost half of respondents to this survey said, "Achieving the right angle of insertion where you are sure the iStent is in- side the canal." When asked about their experience so far in performing cataract surgery with an iStent, the majority of respondents said, "I have been moderately impressed with the pressure reduction." We asked why surgeons are not implanting the iStent currently, and the majority of respondents to this survey said they are still considering whether to add it to their practice. When asked which non-device MIGS procedures they are doing now, more than half of the respondents to this survey said none. Finally, we asked, "As surgeons gain more experience with different MIGS options, which do you think will become the best MIGS approach for treating glaucoma in combina- tion with cataract surgery?" Two answers were nearly tied: trabecular bypass (the iStent or Hydrus) and ciliary body device (the CyPass or iStent Supra).

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