Eligibility Criteria

Inclusion criteria included age 18 to 85 years, previous trabeculectomy and/or cataract extraction with intraocular lens implantation, and intraocular pressure (IOP) ≥18 mm Hg and ≤40 mm Hg on maximum tolerated medical therapy. Exclusion criteria included no light perception vision, pregnant or nursing women, active iris neovascularization or proliferative retinopathy, iridocorneal endothelial syndrome, epithelial or fibrous downgrowth, aphakia, vitreous in the anterior chamber for which a vitrectomy was anticipated, chronic or recurrent uveitis, severe posterior blepharitis, unwillingness to discontinue contact lens use after surgery, previous cyclodestructive procedure, prior scleral buckling procedure, presence of silicone oil, conjunctival scarring precluding a superior trabeculectomy, and need for glaucoma surgery combined with other ocular procedures or anticipated need for additional ocular surgery. Only 1 eye of eligible patients was included in the study.

Randomization and Treatment

The TVT Study was conducted at 17 clinical centers. Eligibility was independently confirmed at the Statistical Coordinating Center. Patients enrolled in the study were randomized to placement of a 350-mm ² Baerveldt glaucoma implant or trabeculectomy with MMC. Randomization was performed using a permuted block design stratified by clinical center and type of previous intraocular surgery. Neither the patient nor the clinician was masked to the randomization assignment during follow-up.

A 350-mm ² Baerveldt glaucoma implant was placed in the superotemporal quadrant in all patients randomized to the tube group. A limbus-based or fornix-based conjunctival flap was dissected, and the implant was sutured to sclera 10 mm posterior to the limbus. The Baerveldt tube was completely occluded to temporarily restrict flow through the device until encapsulation of the plate occurred. The surgeon was given the option of fenestrating the tube for early IOP reduction. The Baerveldt tube was inserted into the anterior chamber through a 23-gauge needle track. A patch graft was used to cover the limbal portion of the tube, and the conjunctiva was closed.

All patients randomized to the trabeculectomy group underwent a trabeculectomy with MMC superiorly. A limbus-based or fornix-based flap was created, and a fluid-retaining sponge soaked in MMC (0.4 mg/mL) was applied to the superior sclera for 4 minutes. A partial-thickness scleral flap was dissected, and a paracentesis was made. A block of limbal tissue was excised underneath the trabeculectomy flap. The scleral flap was reapproximated to the scleral bed with interrupted or releasable 10–0 nylon sutures. The conjunctiva was closed, and Seidel testing was performed at the conclusion of the case.

Patient Visits

Baseline demographic and clinical information were collected for enrolled patients. Follow-up visits were scheduled at 1 day, 1 week, 1 month, 3 months, 6 months, 1 year, 18 months, 2 years, 3 years, 4 years, and 5 years postoperatively. Each examination included measurement of Snellen visual acuity (VA), IOP, slit-lamp biomicroscopy, Seidel testing, and ophthalmoscopy. Humphrey perimetry, Early Treatment Diabetic Retinopathy Study (ETDRS) VA, and quality of life using the National Eye Institute Visual Function Questionnaire (NEI VFQ-25) were assessed at baseline and at the annual follow-up visits. A formal motility evaluation was performed in all patients at baseline and at the 1-year and 5-year follow-up visits, and at any visit after 3 months at which the patient reported diplopia. Investigators provided an explanation for loss of 2 or more lines of Snellen VA at follow-up visits after 3 months. Postoperative interventions and surgical complications were documented at each follow-up visit. Additional information was collected for patients undergoing a reoperation, including the date of surgery, type of procedure, and IOP level and number of glaucoma medications immediately prior to reoperation.

Outcome Measures

Outcome measures assessed in the TVT Study include IOP, VA, use of supplemental medical therapy, surgical complications, visual fields, quality of life, and failure. Failure was prospectively defined as IOP >21 mm Hg or less than 20% reduction below baseline on 2 consecutive follow-up visits after 3 months, IOP ≤5 mm Hg on 2 consecutive follow-up visits after 3 months, reoperation for glaucoma, or loss of light perception vision. Reoperation for glaucoma was defined as additional glaucoma surgery requiring a return to the operating room, such as placement of a tube shunt. Cyclodestruction was also counted as a reoperation for glaucoma. Interventions performed at the slit lamp, such as needling procedures and laser suture lysis, were not considered glaucoma reoperations. Eyes that had not failed by the above criteria and were not on supplemental medical therapy were considered complete successes. Eyes that had not failed but required supplemental medical therapy were defined as qualified successes. An independent Safety and Data Monitoring Committee (SDMC) met twice a year to monitor the conduct of the study.

Statistical Analysis

Univariate comparisons between treatment groups were performed using the 2-sided Student t test for continuous variables and the χ ² test, Fisher exact test, or exact permutation χ ² test for categorical variables. Snellen VA measurements were converted to logMAR equivalents for the purpose of data analysis, as reported previously. The time to failure was defined as the time from surgical treatment to reoperation for glaucoma, loss of light perception vision, or the first of 2 consecutive study visits after 3 months in which the patient had persistent hypotony (IOP ≤5 mm Hg) or inadequately reduced IOP (IOP >21 mm Hg or not reduced by 20% below baseline). Treatment comparisons of time to failure and time to reoperation for glaucoma were assessed with the stratified Kaplan-Meier survival analysis log-rank test. Risk factors for failure were evaluated with the Kaplan-Meier survival log-rank test. Multivariate analysis was performed using Cox proportional hazard regression analysis with forward stepwise elimination. A P value of .05 or less was considered statistically significant in our analyses.

Recruitment and Retention

The TVT Study enrolled 212 eyes of 212 patients between October 1999 and April 2004. Randomization assigned 107 patients to placement of a 350-mm ² Baerveldt glaucoma implant and 105 patients to a trabeculectomy with MMC. All patients received their assigned treatment.

Figure 1 shows the progress of patients in the study. In the overall study group of 212 patients, 28 patients (13%) died within 5 years of enrollment. An additional 39 patients (18%) missed their 5-year study visit. During the first 5 years, 13.0% of follow-up visits were missed because of deaths and losses to follow-up. The visit completion rate did not significantly differ by treatment group ( P = .22, χ ² test).

Flow chart of patient progress in the Tube Versus Trabeculectomy Study.

Baseline Characteristics

Table 1 presents the baseline characteristics of study patients. No significant differences in any of the demographic or clinical features were observed between treatment groups at enrollment. Additional information on randomized patients was provided in a previous publication. Similar mean IOPs and glaucoma medications were seen among patients who were and were not lost to follow-up in both treatment groups ( Supplemental Table , available at AJO.com ).

Intraocular Pressure Reduction

Table 2 and Figure 2 provide baseline and follow-up IOP measurements for the tube and trabeculectomy groups. Patients who underwent additional glaucoma surgery were censored from analysis after reoperation. Both surgical procedures produced a significant and sustained reduction in IOP. At 5 years, IOP (mean ± SD) was 14.4 ± 6.9 mm Hg in the tube group and 12.6 ± 5.9 mm Hg in the trabeculectomy group ( P = .12, Student t test; 95% confidence interval −0.5 mm Hg to 4.1 mm Hg). Among patients who completed 5-year follow-up visits, IOP reduction from baseline (mean ± SD) was 10.2 ± 7.4 mm Hg (41.4%) in the tube group ( P < .001, paired t test) and 12.4 ± 7.2 mm Hg (49.5%) in the trabeculectomy group ( P < .001, paired t test). The degree of IOP reduction was similar between the 2 treatment groups at 5 years ( P = .097, Student t test). No significant difference in mean IOP was seen between treatment groups after 3 months. The proportion of patients with IOP ≤14 mm Hg was also similar between the tube and trabeculectomy groups. At 5 years, 39 patients (63.9%) in the tube group and 40 patients (63.5%) in the trabeculectomy group had an IOP of 14 mm Hg or less ( P > .99, χ ² test).

Intraocular pressure (IOP) at baseline and follow-up in the Tube Versus Trabeculectomy Study. Data are presented as mean ± standard error of the mean and are censored after a reoperation for glaucoma.

An additional intent-to-treat analysis was performed, which included patients who required further surgery for glaucoma. No significant difference in mean IOP was present between treatment groups taking into account all medical and surgical management during 5 years of follow-up. At 5 years, IOP (mean ± SD) was 14.3 ± 6.8 mm Hg in the tube group and 13.6 ± 6.2 mm Hg in the trabeculectomy group ( P = .54, Student t test; 95% confidence interval −1.4 mm Hg to 2.8 mm Hg).

Medical Therapy

Table 2 shows the number of glaucoma medications in the tube and trabeculectomy groups at baseline and follow-up. Patients who underwent additional glaucoma surgery were censored from analysis after reoperation. A significant reduction in the use of medical therapy was seen in both treatment groups. The number of glaucoma medications (mean ± SD) decreased from baseline by 1.8 ± 1.8 in the tube group ( P < .001, paired t test) and 1.7 ± 2.0 in the trabeculectomy group ( P < .001, paired t test) in patients who completed 5-year follow-up visits. A significantly greater use of supplemental medical therapy was observed in the tube group compared with the trabeculectomy group at all follow-up visits during the first 2 postoperative years. However, the mean number of glaucoma medications was similar between treatment groups at 3 years and at all subsequent study visits.

No significant difference in the mean number of medications was seen between treatment groups after 5 years of follow-up when patients who underwent additional glaucoma surgery were included in the analysis. The mean number of medications was 1.4 ± 1.3 in the tube group and 1.2 ± 1.4 in the trabeculectomy group at 5 years in an intent-to-treat analysis ( P = .25, Student t test).

Treatment Outcomes

Table 3 presents the outcomes of randomized patients, unadjusted for follow-up time. All patients who completed 5-year follow-up visits and/or had a prior failure were included in this analysis. A significantly higher failure rate was seen in the trabeculectomy group than in the tube group after 5 years. Treatment failure had occurred in 24 patients (33%) in the tube group and 42 patients (50%) in the trabeculectomy group at 5 years ( P = .034, χ ² test adjusted for stratum). In the tube group, 18 patients (25%) were classified as complete successes and 31 patients (42%) were qualified successes. In the trabeculectomy group, 24 patients (29%) were complete successes and 18 patients (21%) were qualified successes. While the tube group had a higher overall success rate after 5 years, the rate of complete success was similar between treatment groups ( P = .58, χ ² test adjusted for stratum).

Kaplan-Meier survival analysis was also used to compare failure rates between the 2 treatment groups, and the results are presented in Figure 3 . The cumulative probability of failure was 29.8% in the tube group and 46.9% in the trabeculectomy group at 5 years ( P = .002, log-rank test adjusted for stratum; hazard ratio = 2.15; 95% confidence interval = 1.30 to 3.56). No significant differences in treatment efficacy were found between strata ( P = .143, test of treatment-stratum interaction).

Kaplan-Meier plots of the probability of failure in the Tube Versus Trabeculectomy Study.

Figure 4 presents the failure rates for the 2 treatment groups using alternative outcome criteria. Patients with persistent hypotony, reoperation for glaucoma, or loss of light perception vision were still classified as treatment failures. However, the upper IOP limit distinguishing success from failure was changed. When inadequate IOP reduction was defined as IOP greater than 17 mm Hg or not reduced by 20% from baseline on 2 consecutive follow-up visits after 3 months, the cumulative probability of failure at 5 years was 31.8% in the tube group and 53.6% in the trabeculectomy group ( P = .002, log-rank test adjusted for stratum; hazard ratio = 2.04; 95% confidence interval = 1.29 to 3.24). When inadequate IOP reduction was defined as IOP greater than 14 mm Hg on 2 consecutive visits after 3 months, the cumulative probability of failure was 52.3% in the tube group and 71.5% in the trabeculectomy group at 5 years ( P = .017, log-rank test adjusted for stratum; hazard ratio = 1.57; 95% confidence interval = 1.09 to 2.26). Significantly higher failure rates were observed in the trabeculectomy group compared with the tube group when more stringent IOP criteria were used to define success and failure.

Kaplan-Meier plots of the cumulative probability of failure in the Tube Versus Trabeculectomy Study defining inadequate intraocular (IOP) reduction as IOP >17 mm Hg or not reduced by 20% below baseline (Left) or IOP >14 mm Hg (Right). Inadequate IOP reduction criteria must have been present on 2 consecutive visits after 3 months to qualify as failure. Patients with persistent hypotony, reoperation for glaucoma, and loss of light perception vision are classified as failures.

Table 4 lists the reasons for classification as a treatment failure. The most common cause for failure during 5 years of follow-up in both treatment groups was inadequate IOP reduction (IOP >21 mm Hg or not reduced by 20% below baseline on 2 consecutive follow-up visits after 3 months). There were 6 patients in the trabeculectomy group and 1 patient in the tube group who failed because of inadequate IOP reduction and subsequently underwent reoperation for glaucoma. One patient in the trabeculectomy group who failed because of persistent hypotony subsequently underwent a bleb revision for a bleb leak, and a reoperation for glaucoma was later performed when the bleb failed. Seven patients in the tube group and 11 patients in the trabeculectomy group had a reoperation for glaucoma before meeting the failure criteria for inadequate IOP reduction. Among the patients who failed because of inadequate IOP reduction or glaucoma reoperation, the number of medications (mean ± SD) at the time of failure was 2.2 ± 1.4 in the tube group and 2.4 ± 1.1 in the trabeculectomy group ( P = .54, Student t test). Persistent hypotony was the cause of treatment failure in 3 patients in the tube group and 13 patients in the trabeculectomy group. Loss of VA from baseline was seen in 13 patients in the overall group of 16 hypotony failures (81%). Despite failing because of hypotony, 2 patients in the trabeculectomy group and 1 patient in the tube group retained their preoperative level of vision throughout the 5 years of follow-up. When the 3 patients with hypotony and stable vision were reclassified as successes instead of failures, the cumulative probability of failure using survival analysis was 28.6% in the tube group and 44.4% in the trabeculectomy group at 5 years ( P = .003, log-rank test adjusted for stratum). Loss of light perception vision occurred in 1 patient in each treatment group. No significant difference in the distribution of reasons for failure was present between treatment groups ( P = .43, exact permutation χ ² test).

Baseline demographic and clinical features were evaluated as possible predictors for treatment failure and are shown in Table 5 . Treatment failures were pooled from both treatment groups for this risk factor analysis. Only assigned treatment was significantly associated with treatment outcome in univariate analysis ( P = .002, log-rank test). Stratum, age, sex, race, diabetes mellitus, hypertension, lens status, number of previous intraocular surgeries, time since last intraocular surgery, glaucoma type, preoperative number of medications, preoperative IOP, preoperative Snellen VA, and clinical centers were not associated with treatment failure either univariately or in a multivariate model adjusted for treatment. Separate risk factor analyses were also performed for each treatment group, and none of the baseline factors predicted failure for tube shunt surgery or trabeculectomy with MMC.

Reoperation for Glaucoma

Table 6 presents the reoperations that were performed for glaucoma. A higher rate of reoperation for glaucoma was observed in the trabeculectomy group compared with the tube group. The 5-year cumulative reoperation rate for glaucoma using Kaplan-Meier survival analysis was 9% in the tube group and 29% in the trabeculectomy group ( P = .025, log-rank test adjusted for stratum). A total of 18 patients in the trabeculectomy group underwent additional glaucoma surgery, which involved placement of a tube shunt in 15 patients, a bleb revision with tube shunt placement in 2 patients, and a trabeculectomy with 5-fluorouracil in 1 patient. One of the patients who received a tube shunt subsequently underwent a transscleral cyclophotocoagulation in the study eye as a second reoperation for glaucoma. In the tube group, 8 patients had glaucoma reoperations, including placement of a second tube shunt in 4 patients, transscleral cyclophotocoagulation in 3 patients, and endocyclophotocoagulation performed in conjunction with cataract surgery in 1 patient. Repeat transscleral cyclophotocoagulation was performed in the patient who had endocyclophotocoagulation.

TABLE 6

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