EyeWorld Asia-Pacific June 2017 Issue

June 2017 58 EWAP GLAUCOMA MIGS: Understanding the options by Jason Bacharach, MD Dr. Bacharach adds to the growing discussions around MIGS T raditional glaucoma surgeries such as trabeculectomy and tube shunts focus on the subconjunctival space and create external reservoirs, while the newest round of glaucoma devices are making use of the trabecular meshwork and uveoscleral drainage pathways in the eye. It is essential to understand the different outflow paths and the risks/benefits of each to determine which procedure is best for each individual patient. Trabecular meshwork The trabecular meshwork is responsible for 75% of the resistance to aqueous humor outflow, 1 making it a logical place to attempt to reduce IOP. In addition, the natural episcleral venous pressure prevents IOP from declining too precipitously, making hypotony virtually impossible. The iStent Trabecular Micro- Bypass (Glaukos, San Clemente, California) is based on these principles. The 1-mm long stent bypasses the trabecular meshwork and provides access directly to Schlemm’s canal and the collector channels, restoring physiologic outflow through the conventional pathways. Multiple clinical trials and case series have been published demonstrating few or no adverse events following implantation of the iStent. MicroPulse laser cyclophotocoagulation is used to treat a patient who fits its profile. Source: H. George Tanaka, MD space for close to a century through the use of cyclodialysis procedures with rather mixed results. Use of this space may play a role in pressure control with the recent FDA approval of the CyPass Micro- Stent (Alcon, Fort Worth, Texas). FDA investigations are also currently underway for the iStent SUPRA (Glaukos) and the SOLX Gold Shunt (SOLX, Waltham, Massachusetts). Uveoscleral outflow is of interest due to an inherent pressure differential between the anterior chamber and the suprachoroidal space that may aid in removing aqueous from the anterior chamber. 5 Prostaglandins also primarily function via impact on the uveoscleral output system. However, the suprachoroidal space presents risks such as hypotony. A 2-year study of the CyPass demonstrated hypotony prior to 1 month in 15.4% of patients and hypotony after 1 month in 1.9% of patients. 6 If a trabecular meshwork stent is somewhat limited in its lowest possible IOP due to episcleral venous pressure, that same limitation also provides a compelling level of safety that suprachoroidal stents do not have. We see that the more invasive we get with our therapies, the more potential for other side effects. Corneal edema occurs in 2.2%–3.5% of suprachoroidal stent patients, 7 compared to only 1% of trabecular bypass patients. Due to the number of blood vessels in the suprachoroidal space, hyphemas are also of concern. Various trials have shown rates of hyphema of 1.5%, 2.7%, and 6.2% in patients receiving a suprachoroidal stent. 8,9 The U.S. Food and Drug Administration (FDA) pivotal trial had 240 eyes enrolled and found that stent placement did not substantially increase adverse events, nor did it compromise visual outcomes when compared to cataract surgery alone. 2 The most common complications were malpositioning (3%) and obstruction (4%), both predicaments that have a variety of safe and effective options for resolution. It is necessary to keep in mind that in the early studies, we as investigators were just learning how to place the iStent. Without predecessors, we were climbing a fairly steep learning curve. This becomes evident to me when I look back at the results from my patients from the pivotal trial through 2015. I identified 43 eyes in which I placed a single iStent that met the same criteria as the pivotal trial. 3 My patient results improved each year since 2013, with my 2015 patients demonstrating at 1 year a mean drop in IOP of 5.5 mmHg and a mean reduction in medications of 1.0. The improvement in results as we gain experience is incredible. The excellent results seen in my most recent patients are corroborated by a recent study by Thomas Neuhann, MD. 4 These eyes had multiple challenges, including four of them that had previous glaucoma surgery and one had pseudoexfoliation. The mean IOP at baseline is 24.1 mmHg with a mean 1.8 medications. At month 36, he has follow-up for 39 patients who show a mean IOP of 14.9 mmHg on a mean of 0.3 medications. These results are achieved with no cases of hypotony, IOP spikes, or hyphema within 1 month. Suprachoroidal pathway Scientists have been investigating the IOP-lowering potential of the suprachoroidal continued on page 60