Tube Versus Trabeculectomy (TVT) Study

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.

Inclusion Criteria:

- Age 18 to 85 years

- Intraocular pressure greater than or equal to 18 mm Hg and less than or equal to 40
mm Hg

- Previous trabeculectomy, cataract extraction with intraocular lens implantation, or
both

Exclusion Criteria:

- Unwilling or unable to give consent, unwilling to accept randomization, or unable to
return for scheduled protocol visits

- Pregnant or nursing women

- No light perception vision

- Active iris neovascularization or active proliferative retinopathy

- Iridocorneal endothelial syndrome

- Epithelial or fibrous downgrowth

- Aphakia

- Vitreous in the anterior chamber for which a vitrectomy is anticipated

- Chronic or recurrent uveitis

- Severe posterior blepharitis

- Unwilling to discontinue contact lens use after surgery

- Previous cyclodestructive procedure, scleral buckling procedure, or presence of
silicone oil

- Conjunctival scarring precluding a trabeculectomy superiorly

- Need for glaucoma surgery combined with other ocular procedures (eg cataract surgery,
penetrating keratoplasty, or retinal surgery) or anticipated need for additional
ocular surgery