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Trabeculectomy versus viscocanalostomy for primary open-angle glaucoma

Ahmed, Ike K. MD, FRCSC

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Journal of Cataract & Refractive Surgery: October 2005 - Volume 31 - Issue 10 - p 1852
doi: 10.1016/j.jcrs.2005.10.006
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In their comparison of trabeculectomy and viscocanalostomy for primary open-angle glaucoma, Yalvac et al.1 conclude that “trabeculectomy lowered IOP [intraocular pressure] more than viscocanalostomy,”1 although their data and statistics do not support such a statement.

Despite apparent differences between trabeculectomy and viscocanalostomy patients in complete success rate (66.2% versus 52.9% at 6 months and 55.1% versus 35.3% at 3 years), the Kaplan-Meier survival analysis of complete success (P = .2281 [Figure 2]), qualified success (P = .5954 [Figure 3]), and Table 2 show clear lack of statistical significance. Whether this reflects an underpowered study or a truly nonsignificant result, we fail to see how Yalvac and coauthors were able to make a definitive statement about superiority without supportive data in their study. Because 1 group had a higher absolute success rate than the other is not enough to claim a difference; thus, the reason for appropriate sample-size calculation and statistical analysis of significance. The authors fail to describe rationale and details of their sample-size calculation.

The only statistically significant difference between the groups was a higher incidence of hypotony and cataract formation after surgery in the trabeculectomy group.

Although the authors claim this to be a “3-year” study of 50 patients, the mean follow-up was only 18 months. It is not clear how many patients were analyzed at 6 months, 1 year, 2 years, or 3 years, further bringing any long-term analysis into question. In fact, the complete success rate was exactly the same in the trabeculectomy group (55.1%) and the viscocanalostomy group (35.3%) for the 1-, 2-, and 3-year time points. Does this imply there were no more failures after 1 year in both groups?

We also know that goniopuncture in viscocanalostomy, as suture lysis in trabeculectomy, is an important adjunct that can improve postoperative outcomes. Unfortunately, despite the potential benefit and rarity of complications, laser goniopuncture was not performed in the viscocanalostomy group. This would likely have improved the success rate of viscocanalostomy.

I do not think this comparative study demonstrates a superiority of 1 procedure over the other, aside from a reduction of postoperative complications in the viscocanalostomy group versus the trabeculectomy group. A larger sample size is needed to further assess differences.

Ike K. Ahmed MD, FRCSC

Mississiauga, Ontario, Canada


1. Yalvac IS, Sahin M, Eksioglu U, et al. Primary viscocanalostomy versus trabeculectomy for primary open-angle glaucoma; 3-year prospective randomized clinical trial. J Cataract Refract Surg 2004; 30:2050-2057
© 2005 by Lippincott Williams & Wilkins, Inc.