Primary Tube Versus Trabeculectomy Study

Glaucoma surgery is indicated when further intraocular pressure (IOP) lowering is needed
despite the use of maximum tolerated medical therapy and appropriate laser treatment.
Trabeculectomy (or guarded filtration procedure) is the most frequently performed glaucoma
opertion. Eyes with previous ocular surgery and certain secondary glaucomas (e.g. neovascular
glaucoma and uveitic glaucoma) are at greater risk of trabeculectomy failure. Wound healing
modulation with antifibrotic agents, like mitomycin C (MMC) and 5-fluorouracil (5-FU), has
been shown to increase the success of glaucoma filtering surgery in high risk eyes. The use
of MMC and 5-FU has become widespread in clinical practice. The improved efficacy of
trabeculectomy with an adjunctive antifibrotic agent in high risk eyes has prompted their use
in eyes considered to be at low risk for failure. A randomized clinical trial found similar
IOP reduction and surgical complications with the intraoperative application of MMC and 5-FU
in eyes undergoing primary trabeculectomy.

Although antifibrotic agents have increased the likelihood of IOP control following glaucoma
filtering surgery, they have also increased the risk of complications. The prevalence of
bleb-related infections, bleb leaks, and bleb dysesthesia associated with a perilimbal
filtering bleb suggests the need to consider alternative surgical approaches. Favorable
results have been reported with tube shunts (or glaucoma drainage implants), and these
devices have been growing in popularity. In particular, the large surface area of the
Baerveldt glaucoma implant combined with its ease of insertion in a single quadrant offers an
advantage over other tube shunts. Similar surgical results have been reported with tube
shunts and trabeculectomy with MMC or 5-FU when studied separately in similar patient groups.
A comparable rate of serious complications has also been reported for the Baerveldt implant
and trabeculectomy with an antifibrotic agent in a retrospective study.

The Tube Versus Trabeculectomy (TVT) Study is a multicenter randomized clinical trial
comparing the safety and efficacy of tube shunt surgery using the Baerveldt glaucoma implant
and trabeculectomy with MMC in 212 patients with previous ocular surgery. Tube shunt surgery
was more likely to maintain IOP control and avoid persistent hypotony or reoperation for
glaucoma than trabeculectomy with MMC during the first year of follow-up in the TVT Study.
Tube shunt surgery and trabeculectomy with MMC produced similar IOP reduction at 1 year, but
there was less need for supplemental medical therapy following trabeculectomy. There were a
large number of surgical complications during the first year of follow-up in the TVT Study,
but most were transient and self-limited. The incidence of postoperative complications was
higher following trabeculectomy with MMC than tube shunt surgery. However, severe
complications resulting in reoperation and/or vision loss occurred with similar frequency
with both surgical procedures. Vision loss occurred at a similar rate following tube shunt
surgery and trabeculectomy with MMC. Patients who experienced surgical complications had
greater vision loss than patients without complications.

The results of the TVT Study suggest the need to compare the safety and efficacy of tube
shunt surgery and trabeculectomy with MMC in patients at low risk of surgical failure,
including eyes without previous ocular surgery. The Primary Tube Versus Trabeculectomy (PTVT)
Study is a multicenter randomized clinical trial that is similar in design to the TVT Study.
Enrolled patients are randomized to undergo placement of a 350mm2 Baerveldt glaucoma implant
or trabeculectomy with MMC. Baseline characteristics of the study population will be
tabulated for each treatment group. Outcome discrimination between the two treatment groups
will include IOP, surgical complications, visual acuity, visual fields, glaucoma reoperation,
and need for supplemental medical therapy. Data will be collected at the normal postoperative
visits at 1 day, 1 week, 1 month, 3 months, 6 months, 1 year, 18 months, 2 years, 3 years, 4
years, and 5 years after surgery.

Inclusion Criteria:

- Age 18-85 years

- Glaucoma that is inadequately controlled on tolerated medical therapy with IOP greater
than or equal to 18 mm Hg and less than or equal to 40 mm Hg

- No previous incisional ocular surgery

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 ingrowth

- Chronic or recurrent uveitis

- Steroid-induced glaucoma

- Severe posterior blepharitis

- Unwilling to discontinue contact lens use after surgery

- Previous cyclodestructive procedure

- Conjunctival scarring from prior ocular trauma or cicatrizing disease precluding a
superior trabeculectomy

- Functionally significant cataract

- Need for glaucoma surgery combined with other ocular procedures or anticipated need
for additional ocular surgery