Eyeworld

EW GLAUCOMA 104 March 2017 by Jason Bacharach, MD in PAS formation to 3.1% through a 2-year period. 8 In contrast, if a tra- becular stent fails, the pressure tends to return to the patient's baseline rather than escalate to dangerously high levels. Patient facing decisions Glaucoma is a chronic disease that must be attended for the duration of a patient's life, and I think that all of these tools have a place in the glaucoma treatment spectrum. As we learn more about these relatively new stents, we may be able to link them directly to specific patient profiles. The trabecular bypass stent restores and maintains that natural physiological outflow and provides a robust benefit profile with minimal downside risk. Furthermore, it opens the door for a titratable therapy. If I use one or two trabecular bypass stents and feel a patient needs additional pressure control, adding a suprachoroidal stent might be my next step. Time will tell if there are patients best served by a supracho- roidal stent as initial therapy. There is a financial misconcep- tion out there that these stents are expensive and provide little bang for the buck. If you take the four largest iStent studies and combine them, we see 177 patients with an average reduction of 1.31 medications. That makes the median annual savings from medication reduction about $720 per patient. In addition, lack of compliance can lead to the patients' glaucoma getting worse, setting the patient up for more drastic and expensive future therapies. Undoubtedly, these microinva- sive glaucoma surgeries used in ap- propriate patients can provide safe, effective therapies that also make sense financially. EW References 1. Grant WM. Further studies on facility of flow through the trabecular meshwork. AMA Arch Ophthalmol. 1958; 60 (4 Part 1):523–33. 2. Samuelson TW, et al. Randomized evaluation of the trabecular micro-bypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology. 2011;118:459–67. 3. Reiter S. "Impact of surgeon experience on efficacy of trabecular micro-bypass stent with phacoemulsification." Presented at the Barkan Society Meeting, San Francisco. June 2016. 4. Neuhann TH. Trabecular micro-bypass stent Dr. Bacharach adds to the growing discussions around MIGS T raditional glaucoma surger- ies such as trabeculectomy and tube shunts focus on the subconjunctival space and create external reser- voirs, 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 respon- sible for 75% of the resistance to aqueous humor outflow, 1 making it a logical place to attempt to reduce IOP. In addition, the natural epis- cleral venous pressure prevents IOP from declining too precipitously, making hypotony virtually impos- sible. The iStent Trabecular Micro-By- pass (Glaukos, San Clemente, Cali- fornia) 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 demon- strating few or no adverse events following implantation of the iStent. The U.S. Food and Drug Administra- tion (FDA) pivotal trial had 240 eyes enrolled and found that stent place- ment did not substantially increase adverse events, nor did it compro- mise visual outcomes when com- pared to cataract surgery alone. 2 The most common complications were malpositioning (3%) and obstruc- tion (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 prede- cessors, 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 mm Hg 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 Neu- hann, 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 mm Hg with a mean 1.8 medications. At month 36, he has follow-up for 39 patients who show a mean IOP of 14.9 mm Hg on a mean of 0.3 med- ications. 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 space for close to a century through the use of cyclodi- alysis procedures with rather mixed results. Use of this space may play a role in pressure control with the re- cent FDA approval of the CyPass Mi- cro-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 differ- ential between the anterior chamber and the suprachoroidal space that may aid in removing aqueous from the anterior chamber. 5 Prostaglan- dins also primarily function via impact on the uveoscleral output system. However, the suprachoroidal space presents risks such as hypo- tony. 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 limita- tion 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 supracho- roidal 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 A long-term issue of concern is the potential for peripheral anterior sequelae (PAS). When we create these passageways into the suprachoroidal space, an abrupt closure of the cleft can cause a high spike in IOP. The CyCLE trial showed PAS formation at 10%, 9 the COMPASS trial showed a reduction MIGS: Understanding the options The iStent is placed in the angle intraoperatively, as an adjunct to cataract surgery. Source (all): Jason Bacharach, MD continued on page 106

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