TREATMENT OUTCOMES IN THE TUBE VERSUS TRABECULECTOMY (TVT) STUDY AFTER FIVE YEARS OF FOLLOW-UP

Gedde SJ, Schiffman JC, Feuer WJ, et al1

Summary

TVT Study enrolled 212 patients who were 18 to 85 years of age between October 1999 and April 2004. The multicenter clinical trial included individuals with uncontrolled glaucoma who had prior cataract surgery with IOL implantation and/or failed trabeculectomy and an IOP between 18 and 40 mm Hg. Patients were randomized to receive a 350-mm2 Baerveldt glaucoma implant (Abbott Medical Optics Inc.; n = 107) or to undergo trabeculectomy (n = 105) with mitomycin C 0.4 mg/mL for 4 minutes.

Five years postoperatively, the IOP was 14.4 ±6.9 mm Hg in the tube group and 12.6 ±5.9 mm Hg in the trabeculectomy group (P = .12). Both groups achieved a similar decrease in IOP from baseline (P = .097) and experienced a significant reduction in the number of supplemental glaucoma medications they required. No significant difference was found in the complete success rate (IOP controlled without medication) between the two groups (tube, 25%; trabeculectomy, 29%). The qualified success rate (IOP controlled with additional medical therapy), however, was significantly higher in the tube group (42%) compared with the trabeculectomy group (21%). A significantly higher treatment failure rate was noted in the trabeculectomy group (50% vs 33%; P = .034). The 5-year cumulative reoperation rate for glaucoma was 9% in the tube group and 29% in the trabeculectomy group (P < .025). Significant decreases in visual acuity by Snellen and Early Treatment Diabetic Retinopathy Study (ETDRS) charts were observed in both treatment arms, but no significant difference was found between the two groups. Glaucoma was the most frequent cause of vision loss.

Discussion

How do the results of the TVT Study compare with previous observations?

In recent years, the number of glaucoma drainage devices implanted has increased, whereas the number of trabeculectomies performed has decreased in the United States.2-5 In the TVT Study, the investigators have attempted to determine if the two procedures are equally effective and safe. Previous observations suggested that tube shunt surgery achieved worse IOP control compared with trabeculectomy.6 Because tube shunts were traditionally reserved as a late treatment option or a last resort before cycloablation for refractory glaucoma, the rate of treatment failure could be overestimated.7

What is the relationship between the patient population and the study's outcomes?

The TVT Study compared the effectiveness of tube shunts versus the gold standard (trabeculectomy) in eyes with similar conditions. Albeit a heterogeneous group, these eyes represented a commonly seen glaucoma population that carries moderate surgical risks. The study excluded eyes that were conventionally poor candidates for trabeculectomy such as those with neovascular glaucoma. Contrary to previous thought, the overall success rate was higher in the tube group than in the trabeculectomy group. Nearly two-thirds of patients in either the tube or the trabeculectomy group had an IOP of 14 mm Hg or less at the 5-year follow-up (P = 1.00). Both groups needed fewer additional glaucoma medications postoperatively, even after 5 years. The difference in the number of additional glaucoma medications between the two groups in the early postoperative period no longer existed 2 years postoperatively,8,9 suggesting that, in terms of IOP control, a tube shunt was comparable to trabeculectomy. The authors also noted that the cumulative probability of failure was lower in the tube group (29.8%) compared with the trabeculectomy group (46.9%; P = .002). The leading reasons for treatment failure included inadequate IOP control, reoperation for glaucoma, and persistent hypotony.

It is noteworthy to mention that, since the TVT Study was designed, trabeculectomy has evolved, with lower dosages of MMC's being used,10 which could decrease the risks of wound and bleb leaks and hypotony. On the other hand, the incidence of treatment failure due to inadequate IOP control could be higher for the same reasons.

The TVT Study provides high-level data that support the use of tube shunts—based on both success and failure rates—as an early option for surgical intervention in eyes with previous ocular operations. The benefit of tube shunt surgery as a primary operation for a surgically naïve eye is still unclear. The TVT Study group is recruiting patients for the Primary Tube Versus Trabeculectomy Study. It will be interesting to learn the results of this new study in the future.

POSTOPERATIVE COMPLICATIONS IN THE TUBE VERSUS TRABECULECTOMY (TVT) STUDY DURING FIVE YEARS OF FOLLOW-UP

Gedde SJ, Schiffman JC, Feuer WJ, et al11

Abstract Summary

Gedde et al summarized the postoperative complications and interventions in both the tube and trabeculectomy groups during the 5-year follow-up period. Early postoperative complications were documented in 21% of patients in the tube group and 37% of patients in the trabeculectomy group (P = .012). The most common early postoperative complications included choroidal effusion and shallow or flat anterior chambers. Late postoperative complications occurred in 34% of the patients in the tube group and 36% of the patients in the trabeculectomy group. The most frequently observed late complications in both groups were persistent corneal edema followed by persistent diplopia in the tube group and dysesthesia, bleb leak, or an encapsulated bleb in the trabeculectomy group.

Overall, 43% of the patients in the tube group and 63% of the patients in the trabeculectomy group experienced one or more surgical complications postoperatively (P = .006). The most common serious complication associated with reoperation and/or a loss of 2 or more lines of visual acuity (Snellen) was persistent corneal edema. The rate of reoperation from complications was 22% in the tube group and 18% in the trabeculectomy group (P = .29). The leading reoperations performed included penetrating keratoplasty, pars plana vitrectomy, and shunt revision with a patch graft in the tube group and bleb revision in the trabeculectomy group. Cataract progression was noted in 80% of phakic patients in the tube group and 79% of phakic patients in the trabeculectomy group.

Discussion

What safety profile did the investigators evaluate?

In this companion article to the TVT Study, the authors sought to determine if tube shunts and trabeculectomy are equally safe. The study evaluated the safety profile using four major categories: (1) postoperative interventions, (2) early and late complications (including serious complications and the reoperation rate), (3) visual acuities, and (4) cataract progression. The early intervention numbers were much higher in the trabeculectomy group than the tube shunt group (74 vs 27). If the suture lysis, the injection of 5-fluorouracil, and the removal of the ripcord are considered standard postoperative care instead of postoperative intervention,12 however, the rate of postoperative intervention would be much less frequent, especially in the trabeculectomy group (58 suture lysis). The complication rate was much higher in the trabeculectomy group during the early postoperative phase (< 1 month) but was similar in the late phase. Due to the nature of the individual procedures, each surgery has its own spectrum of complications. Bleb leak and dysesthesia were significantly higher in the trabeculectomy group. Although persistent corneal edema occurred in similar proportions in both groups, only six patients in the tube group underwent Descemet stripping endothelial keratoplasty. The TVT safety study revealed a favorable profile in the tube group during the early postoperative period, but the complication rate was similar to that in the trabeculectomy group over the long term.

The TVT Study found that both the Baerveldt tube shunt and trabeculectomy are reasonable surgical options for eyes that previously underwent surgery. Additionally, the TVT Study did not attempt to provide a one-size-fits-all approach for surgical management. Rather, surgeons must consider multiple factors for each patient to achieve the best possible surgical outcome.

Section Editor James C. Tsai, MD, is the Robert R. Young professor of ophthalmology and visual science and the chair of the Department of Ophthalmology & Visual Science at Yale School of Medicine in New Haven, Connecticut. Dr. Tsai may be reached at (203) 785-2020; james.tsai@yale.edu.

Ji Liu, MD, is a clinical glaucoma fellow and clinical instructor in the Department of Ophthalmology & Visual Science at Yale School of Medicine in New Haven, Connecticut. He acknowledged no financial interest in the products or companies mentioned herein. Dr. Liu may be reached at jiliuw@gmail.com.

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