Eyeworld

EW GLAUCOMA 62 August 2015 by L. Jay Katz, MD A s of 2010, an estimated 2.7 million people in the United States suffer from open angle glaucoma (OAG). 1 While patients with moderate to advanced glauco- ma are generally good candidates for trabeculectomies, those with early or mild OAG can be well served with medications. However, as is often the case when dealing with eye drops, patient compliance is typically poor. 2 Finding options that can improve IOP without having to subject patients to complicated or inconvenient medication schedules or to overly invasive surgical proce- dures is beneficial for patients and physicians alike. For patients with mild to moderate glaucoma the use of microinvasive glaucoma surgery (MIGS) procedures has substantial- ly increased over the past several years. These ab interno procedures have very high safety profiles and rapid recovery time for patients. Most importantly, they can lower IOP to the point that patients no longer need medications. Prospec- tive randomized clinical trials of the iStent (Glaukos, Laguna Hills, Calif.) have established the effectiveness of phacoemulsification and stent placement compared to cataract surgery alone. 3,4 Further follow-up has shown that implantation of the iStent during phacoemulsification has resulted in a significantly lower, long-term decrease in IOP and num- ber of medications used compared to phacoemulsification alone. 5,6 Current study of iStent without cataract surgery While earlier work has shown significant and long-term IOP de- crease following implantation of 1 or 2 iStent devices in combination with phacoemulsification, 3–8 more recent reports have focused on the IOP-lowering ability of iStent sur- gery as a standalone procedure. 9–11 Further, the use of multiple trabecu- lar bypass for additive IOP lowering is based on previous pre-clinical work. 12,13 To examine the effects of stent implantation alone and to compare the effect of 1 versus multi- ple stents, a more recent prospective, randomized study was designed to assess IOP reduction after 1, 2, or 3 stents, implanted as a sole procedure in qualified OAG subjects previous- ly not controlled on 1 to 3 ocular hypotensive medications. Follow-up on this study through 5 years is ongoing. To date, data through 18 months postoperatively are promising. At 12 months, 89% Lowering IOP in early to moderate OAG patients without cataract surgery Dr. Chang injects between 10 mcg and 40 mcg of MMC, depend- ing on the patient's risk characteris- tic for scarring—ethnicity, thickness of the conjunctiva and Tenon's capsule, scarring from previous surgery, and desired postop IOP. The vast majority of cases, however, call for either 10 or 20 mcg injections, he said. For 10 mcg injections, he mixes 0.1 mL of 0.2 mg/mL prepared mi- tomycin solution with 0.1 mL of 1% lidocaine, and injects 0.1 mL of the resulting 0.2 mL mixture. For 20 mcg injections, he injects 0.1 mL of 0.2 mg/mL prepared mi- tomycin solution without mixing in the lidocaine. For 40 mcg injections, he injects 0.2 mL of 0.2 mg/mL of the prepared mitomycin solution. Dr. Chang gave a video presen- tation of his technique at the 2014 Combined Ophthalmic Symposium and offered attendees pearls for adopting the method. "Some people inject using a 30 g needle prior to opening the conjunctiva, and some do it in the preop holding area," he said at the symposium. "The surgical flow led me to make a small snip of the conjunctiva and inject the MMC mixture using a blunt cannula." Dr. Chang thinks this method saves valuable intraoperative time and makes the surgery easier. "The benefit is that you know exactly how much mitomycin you're deliv- ering to the tissue, and it facilitates a wide application of the mitomy- cin," he said. "At the same time it hydrodissects the conjunctiva off the sclera, which aids in your flap dissection." Future directions While MMC is currently the most effective antimetabolite used in glaucoma surgery, there is ongoing research into alternative agents that could provide even better surgical outcomes. Several investigators at the Cullen Eye Institute of Baylor Col- lege of Medicine are focusing on the potential of one such agent—silver nanoparticles. The antimicrobial properties of elemental silver are well known, and the antifibrotic property of silver may be channeled to improve surgical outcomes of trabeculectomy. A 2013 study published in Investigative Ophthalmology & Visual Science showed that topical adminis- tration of silver nanoparticles result- ed in improved bleb function when compared to MMC in a rabbit model of glaucoma filtration surgery. "This is the first time [silver nanoparticle application] has been reported for use in a glaucoma sur- gery," Dr. Chang said. "It has the po- tential to promote bleb survival by decreasing fibrosis or scar formation without the cytotoxicity that occurs with mitomycin." Although these results are pre- liminary, the study authors conclud- ed that silver nanoparticles could become a reasonable alternative to MMC in filtration surgery and could represent a means for long-term sur- gical IOP reduction in the future. EW Reference Butler MR, Prospero Ponce CM, Weinstock YE, Orengo-Nania S, Chevez-Barrios P, Frankfort BJ. Topical silver nanoparticles result in improved bleb function by increasing filtration and reducing fibrosis in a rabbit model of filtration surgery. Invest Ophthalmol Vis Sci. 2013 Jul 24;54(7):4982–90. Editors' note: Dr. Chang has no finan- cial interests related to this article. Contact information Chang: ptchang@bcm.edu Mitomycin-C continued from page 60 Cross-sectional view of the iStent in Schlemm's canal connected to the anterior chamber Source: Glaukos iStent in meshwork

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