EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/91447
40 EW FEATURE February 2011 Cataract/glaucoma combined surgeries November 2012 Glaucoma surgical option may appeal to cataract surgeons by Rich Daly EyeWorld Contributing Writer Surgeons say successful implantation of the first micro-incisional glaucoma device likely depends more on anatomy knowledge than surgical technique S urgeons considering cataract removal for the side benefit of treating mild glaucoma gained a new option last summer. And clinical investigators for the iStent Trabecular Micro-Bypass (Glaukos Corp, Laguna Hills, Calif.), which received FDA approval in June, expect those cataract surgeons to be- come the primary users of the device. "The iStent is a great option for all ophthalmologists doing cataract surgery," said Randy Craven, M.D., associate professor, John Hopkins University. "It offers a trabecular bypass for the lowering of IOP for patients who have mild to moderate open-angle glaucoma undergoing cataract surgery." The relative ease with which the device is implanted, according to Dr. Craven and other experienced sur- geons, and its reversibility make it a good first-step surgical alternative to medical therapy in those patients. The biggest obstacle to cataract surgeons successfully using the iStent, experienced surgeons said, is simple anatomy. "Understanding the anatomy and making sure they understand it would be the biggest challenge," said Jason Bacharach, M.D., in private practice, Santa Rosa, Calif., and an original investigator of the iStent. "Once that is mastered there will be a short learning curve for the actual surgical technique. The big AT A GLANCE • Appropriate for cataract patients with mild to moderate glaucoma • Cataract surgeons should restudy the relevant anatomy and practice gonioscopy • Use small movements of the fingers to insert, restart insertion if strong resistance • The iStent is likely only the first in a coming wave of MIGS devices Suprachoroidal stent now in U.S. clinical trials implanted in the angle thing will be visualization and understanding the anatomy." The less than 1 mm long titanium stent is designed for ab interno placement into Schlemm's canal at the lower nasal quadrant through a small temporal clear corneal incision. Similarly, Steven Vold, M.D., in private practice, Fayetteville, Ark., and a Glaukos investigator who has used iStent technologies for nearly 3 years, agreed that cataract surgeons may face challenges from both the unfamiliar anatomy and the related visualization technologies. Specifically, implantation of the device requires using direct go- nioscopy. This requires surgeons to tilt the operating microscope, mov- ing the surgeon farther away from the patient than is usual for cataract surgeons, Dr. Vold said. Dr. Vold and Transcend Medical (Menlo Park, Calif.) have developed a gonio lens that helps surgeons minimize these surgical challenges. Dr. Bacharach suggested cataract surgeons practice gonioscopy during the course of a routine cataract surgery. "So when you get to the point of actually implanting, you've practiced visualizing the angle with the gonio lens and you are able to visualize the structure comfortably," Dr. Bacharach said. Richard A. Lewis, M.D., a cataract surgeon and glaucoma specialist, Sacramento, Calif., offered the visualization pearl of turning the patients' head opposite to themselves and turning the scope maximally toward themselves. Surgical pearls The standard implantation approach described by experienced surgeons also echoes the low risk theme of the device. That is, the iStent is in- Illustration of the iStent Source (all): Jason Bacharach, M.D. tended for implantation as part of a combined cataract surgery, but surgeons ideally should implant it only after a complication-free cataract removal, Dr. Vold said. Pre-op qualifiers for implanta- tion include the use of one to two glaucoma medications. Dr. Lewis noted that patients with poor glaucoma drug compliance might be especially suited for the device. But the device is not indicated in such patients if they have a history of uveitis or angle recession glaucoma or open-angle with heavy trauma and scarring in the angle. Dr. Vold cautioned that it re- mains uncertain how well it will function in patients with increased episcleral venus pressure; it could produce blood reflux into the ante- rior chamber. There also is concern that pseudoexfoliation could obstruct the device's drainage. Surgical pearls for the iStent include ensuring that the angle is "sufficiently open to view angle structures and landmarks," Dr. Bacharach said. Specifically, he uses Miochol-E (acetylcholine chloride intraocular solution, Bausch + Lomb, Rochester, N.Y.) to bring the pupil down and hyperinflates the anterior chamber with viscoelastic. Surgical pearls offered by Dr. Vold include pressing on the poste- rior lip of the wound to help bring blood into Schlemm's canal, which can help surgeons more easily iden- tify the proper location for the iStent placement. It also is impor- tant to document the pigmentation of the trabecular meshwork before operating in order to best account for individual anatomic variations among patients. Additionally, Dr. Vold suggested a soft approach. "When you insert it, it's a movement with your fingers, not your wrist," he said. "You don't want to have big movements, you want to have complete control." The device should enter at a slight angle and slide gently. If faced with strong resistance, then reposi- tion it and try again, he said. Finally, tap the end of the iStent to ensure it is seated properly. "A little blood reflux through the stent is often a good thing because it lets you know that you are in the right spot," Dr. Vold said. Coming micro-trend Surgeons anticipate that the iStent is likely only the first so-called micro- incisional glaucoma device to which U.S. surgeons will have access in the coming years. For instance, Dr. Craven has clinical experience with the Hydrus Intracanalicular Implant (Ivantis, Irvine, Calif.), which is an even more Schlemm's canal-based device than the iStent. The intracanalicular scaffold for the treatment of primary open-angle glaucoma recently began FDA clinical trials. "The intriguing thing about the Hydrus is that the concept of the device came from cardiovascular surgery with a stent that dilates the canal some," Dr. Craven said. "Again, not sure yet if that is good; it may be. Time will tell on that." The Hydrus 3 clock hour nitinol scaffold is designed to potentially restore aqueous outflow for even more collector channels and aims to lower the intraocular pressure even more than a single iStent, Dr. Vold said. A very different approach is taken by the CyPass (Transcend Medical), which taps into the supra- ciliary space and lowers intraocular pressure by increasing uveoscleral outflow. Enrollement for its pivotal FDA clinical trial is targeted for completion by the end of the year, Dr. Vold said. "It is using an outflow system apart from the meshwork and the canal," Dr. Craven said. Also in FDA trials is the iStent Supra, which is another device that bypasses the trabecular meshwork and aims to enhance the supra- choidal drainage to the scleral space. But the immediate future of U.S. micro-incisional glaucoma surgery will be dominated by the iStent, said the surgeons. continued on page 42