Eyeworld

I MIGS UPDATE N FOCUS 32 | EYEWORLD | JULY 2019 Contact information Do: annado88@gmail.com Grover: dgrover@glaucomaassociates.com Kim: wonkim74@hotmail.com Panarelli: joepanarelli@gmail.com by Chiles Aedam R. Samaniego EyeWorld Contributing Writer in Canada. I was also unaware that there were several other surgeons in the U.S. who started doing this around the same time." Among those surgeons who started using this approach in October 2018 was Dr. Grover. Dr. Grover had been involved in the initial FDA pivotal trial so had plenty of experience using the ab interno technique before incorporating the ab externo technique. The ab externo approach, Dr. Grover said, is an even less invasive way of doing the sur- gery. "You don't actually need to make an inci- sion in the cornea at all. It is a very streamlined method, so it's an efficient way of performing the surgery," he said. "This approach was a revelation," Dr. Kim said. "Its speed, simplicity, and effectiveness at avoiding Tenon's entanglement was a significant advantage over ab interno approaches. The visual recovery was almost instantaneous as the surgery did not require any incisions into the cornea or the conjunctiva. This incision-less ab externo transconjunctival approach has been dubbed the 'XEN-ex' technique." Like air XEN, XEN-ex "dramatically low- ered" Dr. Kim's needling rates compared to ab interno XEN implantation; unlike air XEN it is much easier to perform and teach to residents. "The simplicity of this approach is key," he said. Variations The parallel evolution of the ab externo ap- proach among surgeons has led to variations in the exact technique individual surgeons use. At their practice, Dr. Do and Dr. Panarelli prefer first injecting MMC at 60–80 mcg 10 mm posterior to the limbus, then making a 3–4 clock hour peritomy. "The XEN is then insert- ed via an ab externo approach into the anterior chamber and the peritomy is closed with the stent safely tucked beneath the Tenon's layer," they said. "Performing a limited tenonectomy may decrease the risk of stent obstruction/early failure; however, this may potentially lead to a higher risk of erosion through the conjunctiva." N ew techniques to implant the XEN 45 gel stent (Allergan) have evolved as surgeons try to find ways to optimize the efficacy and safety of the implant as well as the ease of implantation, said Anna Do, MD, and Joseph Panarelli, MD, in corre- spondence. At their practice, they have used various approaches to implant the stent: ab interno into the subconjunctival space (closed approach), ab interno beneath the Tenon's layer (open approach), and ab externo beneath the Tenon's layer (open approach) while using variable doses of mitomycin-C (MMC). The ab interno approach is the tradition- al method for implanting the XEN stent, an FDA-approved microinvasive surgical device for medically refractory open angle glaucoma (mrOAG). Recently, however, surgeons have begun embracing the ab externo approach to make an already minimally invasive procedure even less invasive. EyeWorld consulted Dr. Do and Dr. Panarel- li as well as experts Davinder Grover, MD, and Won Kim, MD, regarding this new approach. Evolving practice patterns Dr. Kim has extensive experience with the device, beginning about 2 years ago using the traditional ab interno technique. "Overall, this worked well but the needling rate was 50%," he wrote. He then tried the "air XEN" technique championed by Iqbal "Ike" Ahmed, MD, which separates the conjunctiva from the underlying Tenon's through pneumodissection to create a supra-Tenon's pocket for the XEN implant. "This is then followed by typical ab interno XEN implantation," he said. Air XEN cut Dr. Kim's needling rate in half but added complexity to the surgery. "In October 2018, I had the thought of trying to implant the XEN stent ab externo without any incisions directly through the con- junctiva in a technique similar to bleb needling," Dr. Kim said. "I was unaware at the time that Sebastien Gagne had been doing this since 2016 The XEN 45 ab externo At a glance • As use of the XEN 45 evolves, surgeons are embracing an ab externo approach to implanting the device, though exact techniques vary. • While some surgeons have almost completely shifted to using an ab externo approach for the XEN 45, it may still be advisable for them to learn ab interno implantation techniques first before exploring ab externo techniques, for which there is currently no manufacturer protocol. • In addition to the XEN 45, the PreserFlo—formerly the InnFocus Microshunt—is expected to significantly impact glaucoma surgical practice, though head-to-head comparison of the two devices is yet to be made. continued on page 34

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