Viscocanalostomy vs. Trabeculectomy: Author reply

Ophthalmology Volume 109, Number 3, March 2002 Viscocanalostomy vs. Trabeculectomy The following two letters address an article that appeared in the February issue of the Journal: Jonescu-Cuypers CP, Jacob PC, Konen W, Krieglstein GK. Primary Viscocanalostomy Versus Trabeculectomy in White Patients with Open-Angle Glaucoma: A Randomized Clinical Trial. (Ophthalmology 2001; 108:254 – 8) Dear Editor: Jonescu-Cuypers et al recently reported the first controlled randomized clinical trial of viscocanalostomy vs. trabeculectomy in medically uncontrolled primary open-angle glaucoma (POAG). We wish to congratulate the authors for proposing a study meant to clarify the role of nonpenetrating surgery, which has rapidly become one of the most debated issues in the field of glaucoma. After comparing the outcome and the complications of the two procedures, the authors concluded that success, defined as an intraoccular pressure (IOP) of ⬍20 mmHg without additional surgery or medication, was 50% in trabeculectomy and 0% in viscocanalostomy only 6 months after surgery. We think that these results should be considered with caution, being so peculiarly different from literature data and may be due to a limited sample size. In fact, according to the review of nonpenetrating glaucoma surgery by the American Academy of Ophthalmology Ophthalmic Technology Assessment,1 all the studies published until now indicate that viscocanalostomy has an IOP-lowering effect, with postoperative IOPs generally in the high-normal range, and with variable, but certainly nonzero, degrees of success. In our experience, at 24 months, the Kaplan-Meier probability of survival between 6 and 21 mmHg was 76%, whereas only 46% of the operated eyes achieved an IOP ⬍16 mmHg (oral presentation at the American Academy of Ophthalmology Glaucoma Subspeciality Day, Dallas, Texas, October 21, 2000). Regardless of any consideration about viscocanalostomy, even trabeculectomy seems to yield an overly unfavorable outcome in Jonescu-Cuypers’ study, considering that the eyes included (POAG; mean age, 62.5 years, with no history of ocular surgery) were typically at low risk of failure of conventional penetrating surgery. For instance, among several others, an article recently published in Ophthalmology2 reports a success rate (Kaplan-Meier, IOP ⱕ21 mmHg on no medication) of 87.1% and 51.3% at 1 and 5 years, respectively, after trabeculectomy with no antimetabolites. Moreover, according to an exhaustive overview of 700 eyes,3 the success of trabeculectomy in the authors’ clinic was 48.6% after a mean follow-up of 16.3 months. The authors themselves state in the Discussion that their personal standard success rate of trabeculectomy is 80% at 6 months. Undoubtedly, viscocanolostomy is a difficult procedure, and a very precise technique is mandatory to achieve success. We certainly believe that the authors, who are highly trained in glaucoma surgery, must have recorded more encouraging results for nonpenetrating surgery in their previous experience to motivate their perseverance in conduct-

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ing more than 120 viscocanalostomies, as reported in the Discussion. ROBERTO G. CARASSA, MD PAOLO BETTIN, MD ROSARIO BRANCATO, MD Milano, Italy Reference 1. Nonpenetrating glaucoma surgery. American Academy of Ophthalmology. Ophthalmology 2001;108:416 –21 2. Rothman RF, Liebmann JM, Ritch R: Low dose 5-Fluoruracile trabeculectomy as initial surgery in uncomplicated glaucoma: long term followup. Ophthalmology 2000;107:1184 –90. 3. Diestelhorst M, Khalili MA, Krieglstein GK: Trabeculectomy: a retrospective follow-up of 700 eyes. Int Ophthalmol 1999;22: 211–20.

Author reply Dear Editor: We agree with Drs. Carassa, Bettin, and Brancato that the study, both with respect to sample size and follow-up time, is not adeqate to describe the therapeutic profile of viscocanalostomy. However, the study was not designed to accomplish that. The goal of the study was to compare the intraocular pressure (IOP)–lowering potency of viscocanalostomy with traditional trabeculectomy using the best possible screening techniques. Inclusion, endpoint, and criteria of complete success were defined in a most stringent way. We tried to substantiate the comparative IOP–lowering potential of both procedures, considering the surgical intervention solely. No IOP-effective medication, no additional surgical adjuncts (i.e., laser goniopuncture, laser suturelysis, digital massage, antimetabolite injection) were allowed in either group. IOP in the operated eye that increased to 21 mmHg or greater on any of the postoperative visits was considered as endpoint and failure. In many of the cases, after analyses of nonperforating glaucoma surgery, “complete success” was defined as IOP less than a certain level without glaucoma medications; however, minisurgical maneuvers of various kinds were used postoperatively in most patients. If the study design of Carassa et al had been narrowed to our criteria, the outcome might have been the same. Carassa et al note that we have performed more than 120 viscocanalostomies, yet published findings on a small series. We made sure to allow adequate time and opportunity to complete the learning curve, and after disappointing clinical experience, we decided on a “hard test” for the procedure: IOP ⬍21 mmHg vs. failure without postoperative medications or any surgical adjuncts, in a randomized, prospective, controlled study design. The inferiority of nonperforating surgery compared with trabeculectomy was so marked that we thought publication, even of such a small study, would be worthwhile. Considering the low success rate of trabeculectomy in our study, the same arguments would be applicable. In an observational study of glaucoma treatment patterns over 2 years comprising nine countries of the industrialized world, 50% of all patients having undergone trabeculectomy were receiving IOP-lowering medication again within 3 months,

Letters to the Editor indicating a 50% complete success rate.1 We believe the discrepancies in the literature relating to nonperforating glaucoma surgery are not as striking if the differences in study designs are taken into account. Most of the comparative studies are in agreement that the IOP-lowering effect of viscocanalostomy is inferior to traditional trabeculectomy, and it still remains to be verified whether this drawback in efficacy is balanced by an advantage in safety on the basis of a conclusive study design.

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CHRISTIAN P. JONESCU-CUYPERS, MD PHILIPP C. JACOBI, MD, PHD WALTER KONEN, MD, PHD GUENTER K. KRIEGLSTEIN, MD, PHD Cologne, Germany Reference 1. Hitchings RA. Efficacy of glaucoma treatment—the role of trabeculectomy. In: Jo¨ nsson B, Krieglstein GK, eds. Primary Open-angle Glaucoma: Differences in International Treatment Patterns and Costs. Oxford: Isis Medical Media, 1998; Chap. 18.

Dear Editor: In a small, short-term study comparing primary viscocanalostomy versus trabeculectomy in a low-risk population, Jonescu-Cuypers et al1 conclude that trabeculectomy is more effective than viscocanalostomy. We applaud the authors for their initiative in attempting to answer this important question; however, we believe that this study may be flawed for a number of reasons: ● ●

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With only 10 patients in each group, there is a significant possibility that these results were by chance alone. The authors report subjects ranged in age from 31.2 to 79.2 years old, yet do not break down statistics for each type of surgery. With only 10 patients in each group, was there a difference in the age and range between the viscocanalostomy and trabeculectomy groups? There is no comment as to the number of preoperative antiglaucoma medications and duration of therapy for subjects in each group. Although statistics were not provided, mean intraocular pressures (IOP) and cupto-disc ratios were higher in the viscocanalostomy group, thus implying worse severity of disease. It has been reported that duration of preoperative medical therapy may adversely affect IOP lowering after both penetrating and nonpenetrating glaucoma filtering procedures.2– 4 Almost 30% of patients in the viscocanalostomy group failed within 2 weeks of surgery, with 90% failing by 4 months, thus implying failure caused by surgical technique rather than a fibrotic process. In their description of their viscocanalostomy technique, it seems that the authors dissected a Descemet’s window of “about 1 mm” from Schlemm’s canal. This critical step in the procedure provides the bypass route for aqueous drainage, and based on our experience performing more than 200 nonpenetrating procedures, it is often necessary to dissect a larger “trabeculo-Descemet’s window”— often up to 2 mm beyond Schlemm’s canal—to titrate and permit adequate flow to sufficiently lower IOP. Simply unroofing

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Schlemm’s canal with a smaller and potentially inadequate corneal dissection is likely inadequate and could explain such a high incidence of early failures in the viscocanalostomy group in this study as contradicted by our experience and other studies.5– 8 The authors mention, “hemostasis was maintained by irrigation with balanced salt solution.” There is no comment as to whether cautery, which would be deleterious to the mechanism of action of viscocanalostomy more so than trabeculectomy, or whether topical vasopression or POR-8, which would provide improved hemostasis with better visibility (critical for viscocanalostomy) and reduced fibroblastic activation, were used. Indeed, there was bleeding into the conjunctiva in one case of the viscocanalostomy group. It does not seem that the authors performed goniopuncture in any of the viscocanalostomy failures postoperatively, and in fact, resorted to reoperations in three patients (30%) instead. Postoperative neodymium:yttrium–aluminum– garnet goniopuncture of the trabeculo-Descemet’s window is a relatively easy adjunctive procedure and may be needed in up to 41% of nonpenetrating glaucoma procedures and has been reported to successfully lower postoperative IOP in more than 80% of cases.9 Performed in the controlled postoperative period and akin to suture lysis in trabeculectomy, we do not consider the need for goniopuncture to be a “failure” of nonpenetrating procedures. We certainly believe that this factor alone could account for many of the “failures” in the viscocanalostomy group in this study.

We would like to stress that viscocanalostomy is a highly technique-dependent and patient-dependent procedure, and results need to be taken in consideration of these factors. Just as in trabeculectomy, postoperative management and intervention are critical to the success of surgery. Further controlled studies will hopefully definitively determine the success of this new procedure. IQBAL IKE K. AHMED, MD Toronto, Ontario, Canada ALAN S. CRANDALL, MD Salt Lake City, Utah References 1. Jonescu-Cuypers CP, Jacobi PC, Konen W, Krieglstein G. Primary viscocanalostomy versus trabeculectomy in white patients with open-angle glaucoma: a randomized clinical trial. Ophthalmology 2001;108:254 – 8. 2. Lavin MJ, Wormald RP, Migdal CS, Hitchings RA. The influence of prior therapy on the success of trabeculectomy. Arch Ophthalmol 1990;108:1543– 8. 3. Bylsma S. Nonpenetrating deep sclerectomy: collagen implant and viscocanalostomy procedures. Int Ophthalmol Clin 1999; 39:103–19. 4. Dahan E, Drusedau MUH. Nonpenetrating filtering surgery for glaucoma: Control by surgery only. J Cataract Refract Surg 2000;26:695–701. 5. Stegmann R, Pienaar A, Miller D. Viscocanalostomy for openangle glaucoma in black African patients. J Cataract Refract Surg 1999;25:316 –22.

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