EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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34 EW FEATURE February challenges/MIGS May 2013 Glaucoma 2011 What's on the horizon for MIGS? by Michelle Dalton EyeWorld Contributing Writer AT A GLANCE • MIGS devices will likely best serve the mild-to-moderate glaucoma patient. • Safety will be the major sticking point for approval, maybe more so than IOP lowering. • Multiple devices may ultimately be preferred (and approved) over a single device. More devices, multiple devices, and improved techniques are giving surgeons numerous treatment options I n the U.S., few microinvasive glaucoma surgery (MIGS) techniques are currently approved—just the iStent (Glaukos, Laguna Hills, Calif.) and the Trabectome (NeoMedix, Tustin, Calif.). Others are on their way, but are likely two to three years or more from regulatory approval. Studies and interim results from ongoing studies seem to suggest all the MIGS devices work well to reduce intraocular pressure (IOP), but there is limited data available or emerging to address how efficacious these devices might be without concurrent cataract surgery. MIGS are ab interno procedures/ devices that produce minimal trauma and are efficacious with a high safety profile and provide patients with a rapid recovery, said Iqbal "Ike" K. Ahmed, MD, assistant professor of ophthalmology, University of Toronto, Canada. The U.S. pivotal trial on the iStent showed "virtually no measurable difference in safety comparing iStent to cataract surgery alone," said Thomas W. Samuelson, MD, attending surgeon and co-founder, Minnesota Eye Consultants, Minneapolis. On his wish list is the ability to place more than one iStent to provide patients with even more IOP lowering, or be able to place one stent now and place others later in the disease progression. "Modern cataract surgery alone is a great IOP lowering procedure," The Hydrus device implanted in Schlemm's canal The CyPass device in a patient's eye Source: Ivantis said Kuldev Singh, MD, professor of ophthalmology, and director, glaucoma service, Stanford University School of Medicine, Stanford, Calif. "The bar for all of these devices is pretty high—cataract surgery lowers IOP 3-4 mm Hg on average and the effect is sustained for several years. It is up to the developer of each MIGS device to show an incremental benefit that justifies the cost and potential risk of that device." "My hope is that ultimately, we will be able to use two or three iStents in each patient in the U.S.," said Steven Vold, MD, in private practice, Fayetteville, Ark. More recent U.S. clinical trials are evaluating two stents. Dr. Singh said he hopes and expects that some of the devices still under investigation will offer greater IOP lowering than a single iStent and, of course, substantially greater than cataract surgery alone. "The adoption of these devices that are currently in trials will largely depend on their safety profile as well as the associated degree and longevity of IOP lowering," he said. iStent For patients with mild to moderate glaucoma and concurrent cataract, Dr. Samuelson believes the iStent offers an additional IOP lowering effect. The iStent enhances the IOP lowering effect of phaco alone, which helps fill a large chasm that has existed between cataract surgery alone and cataract surgery combined with trabeculectomy. "If you're only using one iStent, it likely needs to be for that mild to moderate glaucoma patient group," Dr. Vold said. Even with some preliminary results anecdotally available, he's unsure if the device will be efficacious in those with more advanced disease or if multiple stents will be better over time. "The iStent has an excellent safety profile," Dr. Ahmed noted, but "some have advocated that you need more than one iStent to get a big effect." In some cases, the results have shown multiple stents and phaco got pressures down into the low teens and reduced the number of medications as well, he said. "The real key with the use of this device is location," he said. Surgeons need to ensure it's in the canal 100% of the time, and then ideally ensure it is placed at or near an aqueous vein. "If there are no collector channels where you've place the iStent, it's not as likely to provide much benefit as if it were next to or at the level of a collector channel," he said. Experienced surgeons should aim for one of those 3-5 larger aqueous veins that come directly off the canal, he suggested. "If you get the iStent near those, then you've really hit the jackpot." Dr. Singh pointed out, however, that for any MIGS device to be successful from a public health perspective, there should be demonstration of incremental, sustained, long-term IOP lowering beyond cataract surgery alone. "Glaucoma is a chronic disease for which patients often Source: Transcend Medical need treatment for decades. Therapies that are long lasting are obviously more likely to have a positive impact on the disease than those that have only been demonstrated to work for a shorter duration." Hydrus The Hydrus (Ivantis, Irvine, Calif.) is the first device to undergo a comparative study to the iStent, Dr. Samuelson said (he is the medical monitor for the initial European Hydrus trial). "I think the FDA will likely use the iStent as a surgical yardstick of sorts by which the other MIGS procedures will be compared," not unlike the use of timolol on the medical side, he said. "The larger area of cannulation of Schlemm's canal with the Hydrus (three clock hours) gives access to more collector channels and theoretically, one would expect a greater IOP lowering effect than is seen with devices that provide access to fewer channels," Dr. Singh said. According to Dr. Vold, other studies will evaluate the efficacy of one Hydrus against multiple iStents. The results of such comparative studies are being "eagerly awaited" by glaucoma specialists, Dr. Singh said. "Those are important studies that will help determine which device is going to work the best," Dr. Vold said. "Right now, it's a little too early to make that assessment." Of the devices under investigation, the Hydrus is most similar to the iStent in that it enhances con-