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Two trabecular bypass devices (iStent, Glaukos Corp.; EyePass, GMP Companies Inc.) are based on scientifically valid principles but await clinical validation through large, randomized trials.
"Trabecular bypass is an intriguing and scientifically valid strategy for IOP reduction," said Dr. Samuelson, a founding partner of Minnesota Eye Consultants, Minneapolis. "IOP reduction without a bleb is highly desirable, but the resistance from Schlemm's canal and the collector channels may limit IOP-lowering. We anxiously await the data from randomized U.S. studies," he added.
The silicone device consists of two tubes fused together. The fused part is placed in the anterior chamber, whereas the ends are placed in the Schlemm's canal in opposite directions.
As of now no published data exist on the titanium device in the United States, and trials have been suspended. "It was a very difficult study design that required a failed trabeculectomy as a prerequisite," Dr. Samuelson said. The device is available in Europe, however, where trials are ongoing.
In the United States, a prospective, randomized trial is under way to compare cataract extraction alone versus cataract extraction with stent implantation in patients with early to moderate glaucoma.
The two devices represent different approaches, and each has merits, Dr. Samuelson said. The external approach has advantages such as direct placement of the device in the canal, which is easy to verify. In addition, the canal can be viscodilated.