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EW FEATURE 52 MIGS roundup • July 2017 increased patient discomfort, Dr. Panarelli said, adding that there's also the likelihood that more needle track passes will induce more scar- ring at the implantation site. When the XEN is coupled with cataract surgery, if the stent is placed immediately after lens removal, the eye is softer and can make stent placement more difficult, Dr. Panarelli said. It's unknown yet if the inflammation associated with cataract surgery will impact long- term stent function, he added. As for needling, Dr. Radcliffe said he needles about a third of his cases but thinks this is because he's trying to get patients to very low pressures without the use of medi- cation. "If I was more likely to toler- ate a pressure of 17 on one drop, then I would be less likely to needle patients," he said. "But because I'm trying to get patients to have pres- sures of 10 off drops, I am needling, and I'm having great efficacy." Dr. Palmberg explained that the dimensions of the XEN were calcu- lated to produce a pressure gradient from the anterior chamber to the subconjunctival space of 8 mm Hg at normal aqueous flow, using the Hagen-Poiseuille equation. This greatly reduces the risk of persistent hypotony compared to trabeculec- tomy. He said that the XEN and the InnFocus MicroShunt (Santen, Osaka, Japan) are the only mini- mally invasive procedures that have produced low to normal average IOPs—11 mm Hg for the InnFocus MicroShunt at 3 years 1 and 12.6 mm Hg for the XEN at 2 years. 2 Dr. Palmberg cited a recent re- evaluation of the Collaborative Ini- tial Glaucoma Treatment Study that suggests achieving pressures in the low teens has an advantage for even modestly damaged POAG patients, based on an average 10% recovery of the visual field and the increased safety of surgical options. 3 The XEN and InnFocus MicroShunt poten- tially offer safer surgical options to reach such pressures, and the Micro- Shunt is currently being compared to MMC trabeculectomy in ongoing FDA and European trials. Dr. Panarelli thinks the best time to needle is when pressures first begin to creep up. "Early needling to disrupt scar tissue formation is easily accomplished as there is still flow through the device, and this can be done in the office," he said, adding that he reserves more aggressive needling for the operating room, ing to remain in there and enough poking under the conjunctiva and enough poking into the [anterior chamber]. … You want to make sure the two lumens are open and not blocked by tissue," Dr. Sheybani said, likening the stent to a straw. He recommended using whatev- er type of anesthesia you prefer and just making sure patients are well anesthetized before starting the case, as movement on their part could compromise stent placement. Before inserting the stent, Dr. Radcliffe uses 40 micrograms—0.2 cc of the 0.2 mg/ml—of mitomycin-C, injecting it very posteriorly and mas- saging it forward. Paul Palmberg, MD, PhD, professor of ophthalmology, Bas- com Palmer Eye Institute, Miami, explained that the use of mitomy- cin-C (MMC) is needed to retard the formation of additional resistance to aqueous outflow in Tenon's capsule or the conjunctiva. "Injecting the MMC allows the procedure to be done in a 'suture- free' manner as no conjunctival incision needs to be made," Dr. Panarelli said. If the XEN is not combined with cataract surgery, Dr. Sheybani said the clear corneal incision should be angled toward the targeted quadrant of stent placement, with the surgeon making sure the injector sits in that position well without hitting the cheekbone or speculum. A second instrument through a paracentesis helps stabilize the inserter as the tip of the needle is poked through the sclera in the eye, which Dr. Sheybani said should be firm with a cohesive viscoelastic. Dr. Sheybani prefers to place the stent well in the subcon- junctival space, which can look like you might poke through the con- junctiva, he acknowledged. If you're worried about that, he recommend- ed creating a small bleb with bal- anced salt solution or viscoelastic to tent it up. With forward pressure on the needle, making sure it doesn't move up or down or side to side, Dr. Sheybani presses the slider until it feels like it won't go any further. "Then you relax your hands very slowly, equilibrate the system, and slowly withdraw the injector out of the eye," leaving the stent in place, Dr. Sheybani said. Dr. Panarelli does not use fluo- rouracil routinely postop, preferring to keep his patients on more potent steroid medications like diflupred- nate. Dr. Radcliffe said digital ocular compression can be used to help XEN flow. "If I have a XEN that's working partially in a patient and [pressure] is starting to creep up, I'll encour- age the patient to compress the eye and to even massage the area over the bleb itself in order to encourage flow," he said. Overall, Dr. Radcliffe said that while XEN implantation does take some finesse, he found the learning curve to be rapid. "Getting the stent in the perfect position away from the cornea in the angle but not near the iris just takes a little intuition and can be achieved in the first few cases," he said. Complications While Dr. Sheybani said intraopera- tive complications are low, postoper- ative complications could arise if the stent is not placed properly. If too much of the stent is left in the anterior chamber, repositioning is required, but this becomes a chal- lenge as the implant is hydrated and not easily advanced, Dr. Panarelli said. When more than 2 mm of the stent is left beneath the conjunctiva, there is a greater possibility that it could become kinked and/or project upward if caught in Tenon's, he added. If reimplantation is needed, the procedure becomes more difficult due to reduced visibility (bleeding from the first pass attempt) and mm Hg on all of the medications. I did XEN Gel Stents in both eyes, and he's now off all of his drops with pressures of 8," Dr. Radcliffe said. "That's an ideal scenario, but now he's going to have a life with almost no hardware in his eye and with good, controlled pressures, and that's what he needed because he's so young. I point out this case because this is his first glaucoma sur- gery after laser trabeculoplasty, so I think this is a first-line approach for patients, and it should be because of its safety profile." Dr. Sheybani said this procedure is suited for patients with the least chance of scarring. He also said a little bit of proptosis is helpful in early cases because it can be difficult to access a deeply set eye. Avoid the XEN all together in those eyes with scarring in the area where the stent would be placed. Dr. Panarelli said he would avoid placing the stent in patients with advanced disease, finding it difficult to achieve low IOPs in those cases. He acknowledged, however, there are some patients with more advanced disease who might insist on avoiding trabeculectomy or tube shunt surgery; in these cases, he would be willing to try the XEN as it has a more reasonable chance of obtaining a low pressure when com- pared to other MIGS procedures. Surgical technique Implanting the XEN is a completely new procedure to everyone who does it, according to Dr. Sheybani. "It's not a surgery that any one surgeon has an advantage for doing. By that I mean whether you are a glaucoma, comprehensive, or cornea [specialist], none of us has an advantage over another because it's so different in how it's done," he ex- plained. "The nice thing is that the risks of intraop complications are so low when you look at studies across the board. It's not that the tech- nique is easy, but the procedure is reproducible and low risk compared to traditional glaucoma surgeries." According to Allergan's website, the implant is injected ab interno through a clear corneal incision with a pre-loaded, single-use injector with a 27-gauge needle. It is positioned with about 2 mm in the subconjunc- tival space, 3 mm left intrasclerally, and 1 mm in the anterior chamber. Dr. Sheybani said one doesn't need to be so dogmatic when it comes to these measurements. "You just want enough of a tunnel to where it's go- XEN continued from page 50 " It's not that the technique is easy, but the procedure is reproducible and low risk compared to traditional glaucoma surgeries. " —Arsham Sheybani, MD

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