Glaucoma surgery is performed when further intraocular pressure (IOP) reduction is needed despite the use of maximum tolerated medical therapy and appropriate laser treatment. Trabeculectomy is generally used as the initial incisional surgical procedure in managing glaucoma. However, eyes in which trabeculectomy has failed are at greater risk of failure with subsequent filtering surgery. Wound modulation with antifibrotic agents, like mitomycin C (MMC) and 5-fluorouracil (5-FU), has been shown to increase the success rate of trabeculectomy in eyes that have undergone previous ocular surgery. Although antifibrotic agents have increased the likelihood of IOP control following filtering surgery, they have also increased the risk of complications. The prevalence of bleb leaks, bleb-related infections, and bleb dysesthesia associated with a perilimbal filtering bleb suggests the need to consider alternatives. Tube shunts (or glaucoma drainage implants) offer an alternative to trabeculectomy in the surgical management of glaucoma, and these devices have been growing in popularity in recent years.
Practice patterns vary in the surgical management of glaucoma in eyes with previous ocular surgery. In 1996, Chen and colleagues conducted an anonymous survey of members of the American Glaucoma Society (AGS) and Japanese Glaucoma Society (JGS) to evaluate use of antifibrotic agents and tube shunts. The survey presented ten clinical situations requiring glaucoma surgical intervention. The majority of respondents (59-83%) preferred trabeculectomy with MMC for the clinical scenarios involving prior ocular surgery, although many of those surveyed elected to use a tube shunt, trabeculectomy with 5-FU, or trabeculectomy without an antifibrotic agent. In 2002, Joshi and associates re-administered the same survey to members of the AGS. Respondents still favored trabeculectomy with MMC, but the percentage usage of tube shunts had significantly increased. The greatest practice pattern shift was observed in patients with previous cataract and glaucoma surgery. In particular, selection of tube shunts as the preferred surgical approach increased from 7% to 22% in eyes with prior trabeculectomy, and increased from 8% to 22% in eyes with prior extracapsular or intracapsular cataract extraction.
The lack of consensus among glaucoma surgeons regarding the use of tube shunts or trabeculectomy with an antifibrotic agent in eyes that have had prior cataract or glaucoma surgery likely relates to the fact that available clinical data has not shown one surgical procedure to be superior to the other. Similar surgical results have been reported with both glaucoma procedures in eyes with aphakia/pseudophakia and failed filters when studied separately. Success rates have ranged from 50% to 88% for tube shunts, and 48% to 86% for filtering surgery with an antifibrotic agent in case series studying aphakic/pseudophakic eyes. Success rates have ranged from 44% to 88% for tube shunts, and 61% to 100% for 5-FU and MMC trabeculectomy in eyes with failed filters. Comparable rates of severe complications have also been reported with tube shunt surgery and trabeculectomy with an adjunctive antifibrotic agent.
The Tube Versus Trabeculectomy (TVT) Study was designed to prospectively compare the safety and efficacy of nonvalved tube shunt surgery and trabeculectomy with MMC. Patients with uncontrolled glaucoma who had prior cataract extraction with intraocular lens implantation and/or failed filtering surgery were enrolled in this multicenter clinical trial and randomized to placement of a 350 Baerveldt glaucoma implant (Advanced Medical Optics, Irvine, CA) or trabeculectomy with MMC (0.4 mg/ml for 4 minutes). The goal of this investigator initiated trial is to provide information that will assist in surgical decision-making in similar patient groups.
