EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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46 EW GLAUCOMA June 2013 February 2011 Glaucoma editor's corner of the world Managing complications of minimally invasive glaucoma surgery by Tony Realini, MD A s MIGS devices and procedures become more popular, avoiding complications becomes increasingly important. These procedures are often combined with cataract surgery, and preserving the rapid recovery of excellent vision is critical to their success. The major advantage of MIGS is that the risk of adverse events is much lower than with other glaucoma procedures such as trabeculectomies and tube-shunts. This month's "Glaucoma editor's corner of the world" deals with the risks associated with these procedures and steps to avoid them. As new procedures gain popularity, problems may arise that were not seen during the clinical trials. This can reflect a wider group of surgeons using the device/procedure and perhaps extending the indications into areas that were not allowed in the controlled clinical trials. Many times expanding the use of a procedure can improve our understanding of how it works and how to enhance its efficacy. However, testing the limits of indications may also increase the risks. If MIGS is found to have the type of excellent safety profile seen in the clinical trials, these devices and procedures may compete with medical therapy in the glaucoma treatment paradigm. Many glaucoma patients may choose to have the iStent or a Trabectome procedure with their cataract surgery if it would mean eliminating a glaucoma eye drop or two from their daily lives. But safety will be critical. So understanding how to avoid complications and treat them when they occur will be a key component in the widespread adoption of MIGS. Reay Brown, MD, glaucoma editor M inimally invasive glaucoma surgery (MIGS) is gaining traction as an add-on procedure to cataract surgery for medically well-controlled glaucoma patients as a means of reducing their medication burden postoperatively. "We now have more options to offer our patients," said Thomas Samuelson, MD, Minneapolis. Procedures such as trabecular ablation using the Trabectome (Neomedix, Tustin, Calif.) or trabecular meshwork bypass stenting using the iStent (Glaukos, Laguna Hills, Calif.) can significantly lower intraocular pressure (IOP) and minimize the need for IOP-lowering drops after surgery. These procedures generally have fewer complications than the more traditional glaucoma operations, such as trabeculectomy or tube-shunt implantation. But occasionally complications do arise, and prompt and decisive management is the key to ensuring superb visual and IOP outcomes. Trabecular ablation complications The Trabectome uses electrocautery to ablate a strip of the trabecular meshwork (TM), removing the juxtacanalicular TM and the inner wall of Schlemm's canal, which is the primary site of aqueous outflow resistance. This allows aqueous to have direct access to the canal, where it then exits the eye via the collector channel system. "Hyphema is one of the most common complications of Trabectome surgery," said Arthur Sit, MD, glaucoma specialist, Mayo Clinic, Rochester, Minn. "Hyphema or microhyphema occurs in up to 75% of patients on postoperative day one." This isn't surprising, he added. "With Trabectome, we are removing the tissues that comprise the blood aqueous barrier, allowing blood that refluxes back from the episcleral veins, through the collector channels, and into Schlemm's canal, direct access to the anterior chamber," he explained. Thus, some reflux is common in the early postoperative period. In fact, it is nearly ubiquitous at the time of surgery, where its occurrence signals successful re- Slit lamp photograph of patient with delayed onset hyphema in the nasal angle after Trabectome surgery Source: Mayo Clinic moval of the impaired outflow pathway. Evacuation of this fresh blood is a standard step in the surgery after the ablation procedure is completed. Interestingly, bleeding at the ablation site can occur weeks or even months after surgery as well. Dr. Sit explained that normally IOP is higher than the episcleral venous pressure in the vessels that receive aqueous from the collector channels, which physiologically prevents blood reflux into the eye. "But reflux bleeding can occur any time this pressure gradient is reversed." Dr. Sit suggested that this may be related to sleep position. "If patients sleep in the lateral decubitus position on the side of the operated eye, IOP is elevated while the eye is being pressed against the pillow," he said. "When they wake up and lift their head, the IOP is immediately lowered, more so than episcleral venous pressure, and a reverse pressure gradient exists favoring reflux." How should this be managed? "Prevention is essentially impossible," Dr. Sit said. Likewise, since the bleeding is not arising from iris vessels, cycloplegia is also of limited value. "This will self-resolve over time," he said. "The keys are to make sure the patient is aware of the possibility and is familiar with the symptoms. There can be IOP spikes associated with these bleeds, and those can be managed medically until the blood resorbs." Less commonly, eyes can have an acute IOP spike immediately following Trabectome surgery. "In published series, about 8% of eyes will have an IOP spike in excess of 10 mm Hg," said Carla Siegfried, MD, Washington University, St. Louis. There are several potential contributing factors that play a role in these spikes, she said. "They can be caused by retention of the ophthalmic viscoelastic device (OVD), hemorrhage, inflammation, or even the topical steroids commonly used in the immediate postoperative period following cataract surgery." "The vast majority of these short-term IOP elevations can be managed medically," she said. An IOP spike can also signal closure of the cleft, which can lead to failure of the ablation procedure. In these cases, gonioscopy can help identify the risk, and pilocarpine can be useful in maintaining the patency of the fistula, she explained. Trabecular bypass complications Paul Harasymowycz, MD, University of Montreal, Canada, has more than three years of experience implanting the iStent. This small luminal device is inserted through the TM into Schlemm's canal and acts as a shunt from the anterior chamber into the canal, bypassing the site of outflow resistance. He typically implants two devices during each procedure. "The common complications include retrograde bleeding, which can be minimized by using an OVD, transitory IOP elevations around 1-2