Eyeworld

EW GLAUCOMA 60 August 2015 by Lauren Lipuma EyeWorld Staff Writer Mitomycin-C in glaucoma surgery: A new delivery method Subconjunctival injection of mitomycin-C hydrodissects the conjunctiva off the sclera, aiding in flap dissection. Source: Peter T. Chang, MD T he use of antimetabolites in glaucoma surgery has been a deal with the devil. We need them to increase the success of trabeculectomies, but their anti-healing properties can lead to sight-threatening complications like infection and hypotony. The problem is fundamental to trabeculectomies since we are trying to create a hole that doesn't fully heal. Without the antimetabolite—primarily mitomycin-C (MMC)—failure rate of the bleb would be much higher. And a trabeculectomy is still the best treatment for advanced glaucoma where MIGS may not achieve low enough pressures. So MMC is a necessary evil. There has been great progress in antifibrotic treatments for glaucoma surgery. In this "Glaucoma editor's corner of the world," Peter Chang, MD, shares his insights about the current technique for MMC delivery. As someone who has witnessed the full history of anti- metabolite use, I have welcomed the MMC injection technique. Five-fluorouracil (5-FU) was the first antifibrotic agent used to reduce scarring of the bleb in glaucoma surgery. Five-FU was a breakthrough in improving the success of trabeculectomies. But it was a great chal- lenge for patients and surgeons. The original protocol called for subconjunctival 5-FU injec- tions twice daily for one week and once daily for a second week. Because of the frequent injections, a 5-FU filter was one of the few operations that residents would try to avoid. In addition to the burden of daily visits, the aggressive injection regimen led to problems with wound leaks, corneal epithelial breakdown, and infection. The single injection of MMC at the time of surgery is a great step forward and the latest in a long series of advances. The other major challenge in trabeculectomies is controlling the flow of aqueous through the flap. The EX-PRESS Glaucoma Filtration Device (Alcon, Fort Worth, Texas) has helped with this, but even experienced surgeons still have cases where the pressure is lower than expected. The anti-healing effects of MMC in these cases can lead to prolonged hypotony. Although MMC may not have directly caused the excess outflow—the surgeon created the flap—the absence of full healing capacity can make it impossible for the eye to recover, and further surgery may be necessary to raise the pressure. It seems like the devil is part of this deal, too. But hope is on the way. There are MIGS devices nearing approval—such as the Xen Gel Stent (AqueSys, Aliso Viejo, Calif.)—that are designed to perform filtering surgery without a scleral flap. The Xen study included the use of MMC at the time of surgery. It will be interesting to see if the Xen and other MIGS approaches to filtering surgery will have fewer complications than traditional trabeculectomies and whether the risks of MMC can be managed more successfully. Reay H. Brown, MD, glaucoma editor Injection of the antimetabolite provides advantages over traditional sponge application S ubconjunctival injection of mitomycin-C (MMC) is emerging as a superior method of delivering the antimetabolite during glaucoma filtering surgery when compared to traditional sponge application. The injection method provides several surgical benefits that translate to potentially better outcomes for the patients, said Peter T. Chang, MD, associate professor of ophthalmology, Cullen Eye Insti- tute, Department of Ophthalmology, Baylor College of Medicine, Hous- ton. While any application of MMC during trabeculectomy can improve surgical success of the procedure, there are several problems associ- ated with the traditional sponge application method. First, there is no standard material or sponge size, which leads to inconsistent and unreliable absorption of MMC into the sponge material, Dr. Chang said. In addition, "stuffing" of the sponge into the subconjunctival space could inadvertently stretch or tear the con- junctiva, and sponge material, when left behind, can cause postoperative complications, he said. By contrast, injecting MMC directly into the subconjunctival space allows for precise delivery of the desired amount of MMC and facilitates a wide application of the antimetabolite, Dr. Chang said. "The injection also hydrates the Tenon's capsule and elevates the tissue to facilitate dissection for the surgical creation of the conjunctival flap," he said. Injection of MMC results in less trauma to the conjunctiva, fewer inadvertent tears, and a shorter op- erating time. In addition, surgeons need no longer worry about leaving behind a sponge. Surgical technique Dr. Chang decided to switch to the injection method after a presen- tation by Michelle Lim, MD, vice chair and medical director, Univer- sity of California Davis Eye Center, at the American Glaucoma Society annual meeting, where she showed success with the technique. continued on page 62 Glaucoma editor's corner of the world

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