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In this new feature, the editors of Advanced Ocular Care identify topics of interest to optometrists that are being discussed in the pages of our sister publications. Please visit www.glaucomatoday.com for the full text of the story in this installment.
Glaucoma Today includes a column, “Landmark Studies,” whose section editor is Ronald L. Fellman, MD. In the February issue, Steven R. Sarkisian Jr, MD, reviewed the data from the Tube Versus Trabeculectomy (TVT) Study. Dr. Fellman wrote, “This study has significantly changed how many glaucoma surgeons choose between implanting a tube shunt and performing a trabeculectomy.”
Dr. Fellman asked Dr Sarkisian several key questions about the study. Some of those appear here.
WHAT QUESTION WAS THE TVT STUDY DESIGNED TO ANSWER?
The TVT Study was designed to compare the safety and efficacy of nonvalved tube shunt surgery to trabeculectomy with mitomycin C (MMC) in patients who had previously undergone intraocular surgery.1-5
WHAT IS THE MOST IMPORTANT CLINICAL TAKE-HOME MESSAGE FROM THE TVT STUDY?
It is more efficacious to implant a glaucoma drainage device to control intraocular pressure (IOP) than to perform a repeat trabeculectomy on patients who have previously had surgery, especially those who underwent trabeculectomy.
HOW HAS THE TVT STUDY CHANGED YOUR SURGICAL APPROACH TO CONTROLLING GLAUCOMA?
Most ophthalmologists desire to practice evidencebased medicine. For many of us, however, our surgical approaches are often predicated on biases established during our training, through our surgical experience, and from our patient population. I have routinely implanted primary glaucoma drainage devices in patients with refractory glaucoma and in all patients in whom previous glaucoma filtration surgery failed. The TVT Study affirmed my existing surgical approach to uncontrolled glaucoma, because it is has never been my typical treatment paradigm to perform a second trabeculectomy after the first trabeculectomy has failed.
MANY OPHTHALMOLOGISTS THOUGHT THE IOP WOULD BE HIGHER IN THE TUBE GROUP. WHY DO YOU THINK THIS WAS NOT THE CASE?
It is important to point out that the patients in the TVT Study were not undergoing primary glaucoma surgery. Moreover, all patients with refractory glaucoma were ineligible for the study. Essentially, the participants in the TVT Study were the patients who typically do the best with a glaucoma drainage implant in my practice. These “easier” or less refractory glaucoma patients fall into one of two groups. The first includes individuals who underwent cataract surgery and who had a previous scleral tunnel incision with conjunctival scarring. The second comprises patients in whom previous trabeculectomy failed. None of the patients in the study had congenital, neovascular, traumatic, or uveitic glaucoma. I think this largely explains the slight edge that tube shunts had over trabeculectomy in the TVT Study, and the older age of this patient population might skew the results. One of the great things about the investigation, however, is the primary take-home message that patients in whom previous trabeculectomy failed and who need further surgery to lower their IOP should have a tube shunt rather than another trabeculectomy.
MMC 0.4 mg/mL WAS USED FOR 4 MINUTES IN THE FILTRATION ARM OF THE TVT STUDY. THE HYPOTONY RATE WAS 13% COMPARED WITH 9% IN THE COLLABORATIVE INITIAL GLAUCOMA TREATMENT STUDY. HAS THE USE OF MMC CHANGED, AND WHAT DO YOU CURRENTLY RECOMMEND?
I use MMC 0.4 mg/mL for eyes that have a very thick Tenon capsule. To my knowledge, few surgeons currently use MMC for 4 minutes. This length of application may account for the long-term hypotony rate reported in the TVT Study. I no longer use sponges or cut Weck-Cel spears (Beaver-Visitec International) to apply MMC, and I typically inject the antifibrotic agent before the start of the case. If I am not using an Ologen implant, I inject a mixture of MMC 0.4 mg/mL with 2% lidocaine and epinephrine. First, I make a small snip at the limbus. Next, with a 27-gauge cannula, I inject approximately 0.2 mL of this mixture 10 to 15 mm posterior to the limbus and then massage it forward.
DID THE TVT STUDY PROVIDE INFORMATION ABOUT VISUAL FIELD OUTCOMES OR OPTIC NERVE CHANGES? IF NOT, IS IT FORTHCOMING?
The outcome measures for the TVT Study primarily looked at IOP, vision, the reoperation rate for glaucoma, the use of supplemental medical therapy, surgical complication rates, visual field outcomes, and quality of life. Interestingly, in the published TVT analysis of surgical failure, the primary outcome measurements were IOP and vision. There was no visual field criterion used to define failure. In my careful review of the multiple TVT publications, there has not been any discussion of the visual fields for these patients. The TVT Study team is preparing a manuscript on visual field outcomes as well as quality of life. Other articles related to cost analysis and glaucoma reoperations in the TVT Study are forthcoming (Steven Gedde, MD, personal communication, September 2012).
Section Editor Ronald L. Fellman, MD, is a glaucoma specialist at Glaucoma Associates of Texas in Dallas and clinical associate professor emeritus in the Department of Ophthalmology at UT Southwestern Medical Center in Dallas. Dr. Fellman may be reached at (214) 360-0000; email@example.com.
Steven R. Sarkisian Jr, MD, is the director of the glaucoma fellowship at the Dean A. McGee Eye Institute, and he is a clinical associate professor of ophthalmology at the University of Oklahoma College of Medicine in Oklahoma City, Oklahoma. Dr. Sarkisian may be reached at (405) 271-1093; firstname.lastname@example.org.
- 1. Gedde SJ, Schiffman JC, Feuer WJ, et al. Treatment outcomes in the Tube Versus Trabeculectomy (TVT) Study after five years of follow-up. Am J Ophthalmol. 2012;153(5):789-803.
- 2. Rauscher FM, Gedde SJ, Schiffman JC, et al; Tube Versus Trabeculectomy Study Group. Motility disturbances in the Tube Versus Trabeculectomy Study during the first year of follow up. Am J Ophthalmol. 2009;147(3):458-466.
- 3. Gedde SJ, Schiffman JC, Feuer WJ, et al. Three-year follow-up of the Tube Versus Trabeculectomy Study. Am J Ophthalmol. 2009;148(5):670-684.
- 4. Kanner E, Netland PA, Sarkisian SR, Du H. Ex-Press miniature glaucoma device implanted under a scleral flap alone or in combination with phacoemulsification cataract surgery. J Glaucoma. 2009;18(6):488-491.
- 5. Sarkisian SR. Ologen. Paper presented at: the Annual Meeting of the AGS; March 2, 2011; Dana Point, CA.