We read the editorial by Katz and associates with great interest and appreciate their perspective. So that readers may better judge the perils of glaucoma surgical outcome analysis, we offer some clarifications and corrections regarding our data.
Katz and associates state that “the larger proportion of patients that do not require any glaucoma medication in the trabeculectomy group may be an important long-term advantage for this procedure.” The Tube Versus Trabeculectomy Study did find greater use of supplemental medical therapy in the tube group compared with the trabeculectomy group after 1 year of follow-up, and the trabeculectomy group had a higher rate of complete success (i.e., no adjunctive medical therapy) at 1 year. However, a progressive increase in the use of medical therapy was observed in the trabeculectomy group with subsequent follow-up, whereas the number of medications remained stable in the tube group. The mean number of medications was similar between the tube group and the trabeculectomy group at 3 years, and the rate of complete success was not statistically different between treatment groups after 3 years of follow-up. Although a lesser requirement for medical therapy may be a short-term advantage of trabeculectomy over tube shunt surgery, this benefit does not seem to persist with longer follow-up.
The editorial quotes a 10% rate of diplopia after tube shunt surgery in the Tube Versus Trabeculectomy Study. The actual incidence of diplopia was 5% during the first 3 years of follow-up. New motility disturbances were detected in 9.9% of patients in the tube group at 1 year, but only a subset of these patients experienced diplopia. We agree that diplopia is an important complication after tube shunt surgery.
Postoperative complications occurred more frequently after trabeculectomy with mitomycin C than after tube shunt surgery. However, all complications are not equal in severity. We had considered weighting complications, as suggested by Katz and associates. However, there are difficulties in using this approach because individual complications have a broad range of severity. For example, suprachoroidal hemorrhage and diplopia were listed in the editorial as complications producing greater concern. However, diplopia may represent an infrequent symptom elicited only in extreme gaze or a disabling problem that is constantly present, and a suprachoroidal hemorrhage may be visually devastating or self-limited and without sequelae. We instead chose to define serious complications as those that were associated with a reoperation to manage the complication, loss of 2 lines or more of Snellen visual acuity, or both. The rate of serious complications was similar between the tube group and the trabeculectomy group. It is unclear why the authors of the editorial conclude that “although overall complication rates favor the tube group, when the more serious sequelae are separately examined there may be more concerns in the tube shunt group.”
We appreciate the insightful comments on the Tube Versus Trabeculectomy Study from Katz and associates. The study offers a wealth of data comparing 2 commonly performed glaucoma procedures. These data should be analyzed and interpreted critically, as was done in the editorial. Additional follow-up is needed to evaluate fully the relative merits of trabeculectomy with mitomycin C and tube shunt surgery in patients who have undergone previous cataract extraction, for whom filtering surgery has failed, or both.