SEP 2012

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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September 2012 February 2011 EW GLAUCOMA Alternatives to trabeculectomy: What works? by Tony Realini, M.D. T rabeculectomy has been the clinical standard glaucoma operation since its intro- duction more than 40 years ago. It is far from perfect, with a moderately high failure rate and a long list of potentially sight- threatening complications that can appear years after surgery. In recent years, many modifications have been proposed and some novel procedures developed to enhance or replace trabeculectomy. Some have achieved regulatory approval in the U.S., but none has unseated trabeculectomy as the preferred procedure for open-angle glaucoma. At the 2012 World Ophthalmology Congress in Abu Dhabi, a panel of expert glaucoma surgeons discussed the status of new techniques for glaucoma surgery. Modulating wound healing The principle cause of trabeculec- tomy failure is scarring. If physicians could better modulate the wound- healing process, the success rate of filtering surgery would improve. A new product may play a role in this modulation. "Ologen [Optous, Roseville, Calif.] is an extracellular matrix used to modulate wound healing," said Steve Sarkisian, M.D., Dean McGee Eye Institute, Oklahoma City. "It consists of atelocollagen crosslinked with glycosaminoglycans. It comes in a flat disc measuring 12 mm in diameter by 1 mm thick. When placed under Tenon's capsule at the completion of the operation, it guides fibroblasts to grow through a matrix scaffold in a less random fashion so they don't create a ring of steel around the base of the bleb." This ring of steel limits the size of the bleb, leading to highly ele- vated, thin-walled ischemic blebs that filter poorly and are prone to leaking, he said. The implant modu- lates early post-op wound healing but is biodegradable and generally melts away between 3 and 6 months after surgery, he said. "I now use it in 90% of my pa- tients," Dr. Sarkisian said. "There are a few exceptions. I will avoid it and use mitomycin-C instead in patients with very thick Tenon's." He shared a few surgical pearls for using Ologen. "It needs aqueous to flow through it, so tie the flap loosely. And if you need to perform Locking the tensioning suture Source: Matthias Grieshaber, M.D. suture lysis afterward, you may need the Blumenthal lens [Volk Optical, Mentor, Ohio], which can compress both Tenon's and the Ologen for better visualization." Avoiding the bleb "Traditional procedures require a full-thickness hole to develop a transscleral aqueous pathway and a filtration bleb," said Doug Rhee, M.D., Massachusetts Eye and Ear Infirmary, Boston. "These proce- dures lower IOP well but are associ- ated with significant complications." For many glaucoma surgeons, a procedure that avoids creating a fil- tering bleb is the holy grail. Several procedures can lower IOP without bleb formation. Among those more commonly performed in the U.S. are canaloplasty (iScience, Menlo Park, Calif.) and the Trabectome proce- dure (NeoMedix, Tustin, Calif.). "Canaloplasty evolved from viscocanalostomy," said Matthias Grieshaber, M.D., University of Basel, Switzerland. "Canaloplasty targets more of the circumference of Schlemm's canal, including the infe- rior quadrant where the majority of collector channels are." The procedure involves thread- ing an illuminated microcatheter through the canal under a double scleral flap, using the cannula to place a suture—usually a 9-0 or 10-0 nylon—through the canal, then tying it under the flaps to put the internal wall of Schlemm's canal under stretch. "We don't know the exact mechanism by which canaloplasty lowers intraocular pressure [IOP]," he said, but there are three possible ways. "First is the potential for out- flow through the trabeculodescemet window created during flap con- struction," he said. "Second is the possibility that 360-degree viscodila- tion of the canal widens the canal and microdisruption of the inner and outer canal walls decreases out- flow resistance. Third is the likeli- hood that the suture tension has a possible pilocarpine-like effect in widening and maintaining the width of the canal." He said that getting the tension right on the suture can be tricky at first. "Initially we confirmed the ten- sion with ultrasound biomicroscopy, but with practice it becomes intu- itive. One tip is that is always takes more tension than you think, but you must be careful not to pull too hard or you can cheesewire through the meshwork and essentially perform trabeculotomy." "It's a rewarding procedure," Dr. Grieshaber said. "There are no antimetabolites, no bleb, there's a faster recovery time with less intense post-operative management, and no need for massage, suture lysis, or needling." The Trabectome procedure is also blebless. It differs from standard trabeculotomy in that the trabecular meshwork and inner wall of Schlemm's canal are not merely in- cised but are ablated using electro- cautery, explained Dr. Rhee. "This creates a direct communication between the anterior chamber and the collector channels, effectively bypassing the juxtacanalicular obstruction responsible for reduced outflow and elevated IOP." "As a stand-alone procedure, Trabectome is very safe and quite effective in the short term," he said. "But long-term results are disap- pointing. In our experience, the 1- and 2-year success of Trabectome is about 40% and 20%, respectively. The issue is wound healing. That's why this procedure fails." "It has limited effectiveness as a standalone procedure, but it may be better combined with cataract surgery," Dr. Rhee suggested. EW Contact information Grieshaber: mgrieshaber@uhbs.ch Rhee: dougrhee@aol.com Sarkisian: steven-sarkisian@dmei.org 77

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