EyeWorld Asia-Pacific September 2017 Issue

Clarifying the optimal surgical care process for glaucoma W hen the tube versus trabeculectomy (TVT) study reported its ini- tial findings a decade ago, we learned that tube shunt surgery provided comparable reduc- tions in mean intraocular pressure (IOP) to trabeculectomy but higher success rates than trabeculectomy and fewer complications. Long- term follow-up of the TVT cohort confirmed these findings through 5 years of postoperative observa- tion. These findings came as the popularity of tube shunt surgery was already climbing and the number of trabeculectomy surgeries was falling. It seemed a paradigm shift was in the making, in which tubes could be the preferred first-line surgery for glaucoma, replacing trabeculectomy. The TVT study was not designed to evaluate primary glaucoma surgery. Its participants had all previously undergone intraocular surgery, either cataract extraction with intraocular lens implantation or trabeculectomy. As a result, TVT was unable to answer a fundamen- tally important clinical question: Given that most glaucoma patients who advance to surgical interven- tion will only need one incisional procedure in their lives, what is the best first glaucoma operation for these patients? To close this gap, the TVT inves- tigators designed and conducted the primary tube versus trabeculectomy (PTVT) study. This was discussed at the 2017 American Glaucoma Soci- ety meeting. Primary tube versus trabeculectomy study by Tony Realini, MD, MPH Efficacy in the PTVT study According to Steven Gedde, MD , Miami, “PTVT was designed to compare the efficacy of tube shunt surgery versus trabeculectomy in eyes with medically uncontrolled glaucoma and no prior incisional ocular surgery.” Eligible subjects had IOP between 18 and 40 mmHg on maximally tolerated medical therapy, he added. Subjects were randomly assigned to undergo either tube shunt surgery with a 350-mm 2 Baerveldt glaucoma implant (Johnson & Johnson Vision, Santa Ana, California) or superior trabeculectomy with mitomycin-C 0.4 mg/mL applied for 2 minutes. The key outcome measures included IOP reduction, the need for IOP-low- ering medicines, and the cumulative probability of failure of the surgical procedure. In the TVT and PTVT studies, surgical failure was defined as any of the following: IOP > 21 mmHg or reduced less than 20%, IOP < 5 mmHg, reoperation for glau- coma, or loss of light perception. Overall, 242 subjects were ran- domized in the study. Their average age was 61.4 years, two-thirds were male, half were African American, 90% had primary open-angle glau- coma (POAG), and the visual field mean deviation averaged –14.6 dB. Of this cohort, 225 subjects com- pleted the 1-year follow-up period. “Greater IOP reduction was achieved with fewer IOP-lowering medications in the trabeculectomy group,” said Dr. Gedde, the principal investigator of both the TVT and PTVT studies. Mean IOP in the tra- beculectomy group was 12.4 mmHg versus 13.8 mmHg in the tube group ( p =0.012), using an average of 0.9 versus 2.1 IOP-lowering medica- tions, respectively ( p <0.001). “Also, trabeculectomy with mitomycin-C had a higher success rate than tube surgery at 1 year,” he said. Failure occurred in 17.3% of tube shunt eyes versus 7.7% of trab- eculectomy eyes ( p =0.012). The most common failure criterion met was inadequate IOP reduction. Recogniz- ing that a target of 21 mmHg or less might not be clinically adequate for many patients, the research team also determined failure rates for lower target pressures. For IOP > 17 mmHg, failure rates in the tube and trabeculectomy groups were still significantly different at 20.6% and 9.6%, respectively ( p =0.012), while for IOP > 14, failure rates were in- significantly different at 28.1% and 20%, respectively ( p =0.15). Interestingly, low IOP was a sig- nificant risk factor for failure in the tube group. “Patients with a lower IOP at baseline were the ones who benefited more from trabeculectomy than tube shunt surgery,” Dr. Gedde said. Safety in the PTVT study “Postoperative complications oc- curred in 25 (20%) patients in the tube group and 39 (33%) patients in the trabeculectomy group,” said Ike Ahmed, MD, Toronto. Com- mon postoperative complications included choroidal effusions, anterior chamber shallowing, and wound leaks, he said. Reoperation was necessary in seven eyes with trabeculectomy (6%) versus only one eye with a tube shunt (0.8%; p =0.024). Short of reoperation, “the most common intervention in the tube shunt group was rip cord removal, and in the trabeculectomy group was laser suture lysis,” Dr. Ahmed said. There were no significant between-group differences in visual acuity changes, he added. Practical applications “The results of this study at 1 year preliminarily suggest that trab- eculectomy is a more effective procedure, but safety may favor tube surgery,” Dr. Gedde said. Greater IOP reduction and surgical success were achieved with fewer medications in patients randomized to trabeculec- tomy with mitomycin-C. However, early postoperative complications (i.e., complications developing in the first month after surgery) and serious complications (i.e., compli- cations producing vision loss and/or requiring a reoperation to manage the complication) occurred more frequently after trabeculectomy compared with tube shunt surgery. “The most interesting find- ing, in my opinion, came from an analysis of the risk factors for failure,” Dr. Gedde said. “Patients with low preoperative IOP do poorly with tube shunt surgery as a primary procedure.” He added that a post hoc analysis of the original TVT data set showed a similar effect. “Practice patterns are shifting in the surgical management of glaucoma,” Dr. Gedde said. “The PTVT study provides valuable information to guide selection of a primary inci- sional glaucoma procedure.” EWAP Editors’ note: Dr. Ahmed has finan- cial interests with Johnson & Johnson Vision. Dr. Gedde has no financial interests related to this article. Contact information Ahmed: ikeahmed@mac.com Gedde: sgedde@med.miami.edu September 2017 54 EWAP GLAUCOMA