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Trabeculectomy versus viscocanalostomy for primary open-angle glaucoma
LETTERS
REFERENCES 1. Atchison DA. Pseudoaccommodation with forward movement of IOLs [letter]. J Cataract Refract Surg 2005; 31:11 2. Huber C. Myopic astigmatism as a substitute for accommodation in pseudophakia. Doc Ophthalmol 1981; 52:123–178 3. Donders FC. On the anomalies of accommodation and refraction of the eye; translated from the author’s manuscript by WD Moore. London, New Sydenham Society, 1864 4. Johnson L. A new theory of accommodation. Arch Ophthalmol (old series) 1924; 53:426–430 5. Coleman DL. Unified model for accommodative mechanism. Am J Ophthalmol 1970; 69:1063–1079 6. Coleman DJ. On the hydraulic suspension theory of accommodation. Trans Am Soc Ophthalmol 1986; 84:846–868 7. Thornton SP. Lens implantation with restored accommodation. Curr Canadian Ophthalmic Pract 1986; 4:60, 62, 82 8. Thornton SP, inventor; Eye Technology, Inc., assignee. Intraocular lens for capsular bag implantation. US patent 4 718 904. January 12, 1998 9. Thornton SP. Anterior ciliary sclerotomy with tissue barriers; the scleral approach to presbyopia treatment. Highlights Ophthalmol 2005; 33 (1): 19–20 10. Nawa Y, Ueda T, Nakatsuka M, et al. Accommodation obtained per 1.0 mm forward movement of a posterior chamber intraocular lens. J Cataract Refract Surg 2003; 29:2069–2072 11. Rana A, Milller D, Magnante P. Understanding the accommodating intraocular lens. J Cataract Refract Surg 2003; 29:2284–2287
Trabeculectomy versus viscocanalostomy for primary open-angle glaucoma 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 Z .2281 [Figure 2]), qualified success (P Z.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?
1852
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 REFERENCE 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
Reply: I appreciate the comments by Ahmed; however, I would like to clarify some points. First, we concluded that ‘‘[p]rimary trabeculectomy lowered IOP more than viscocanalostomy in primary open angle glaucoma patients.’’ From Table 2, which shows the mean postoperative IOP values, it is clear that the mean IOP was lower in the trabeculectomy group than in the viscocanalostomy group: P Z .03 at 1 day, P Z.002 at 1 week, P Z .005 at 3 months, and P Z .027 at 1 year. We all agree that the groups did not show a statistically significant difference in terms of surgical success criteria, and we did not conclude that the trabeculectomy group achieved a statistically significant surgical success rate compared with the rate in the viscocanalostomy group in the Discussion. We stated that it is difficult to compare intermediate and long-term follow-up studies because the success criteria are not uniform and also that the mean number of antiglaucoma medications was significantly lower in the trabeculectomy group (P Z .004). Table 1 shows the detailed number of follow-ups in our study group. The question of why we did not perform laser goniopuncture in the viscocanalostomy group is explained in the Discussion. The study was to compare the IOP-lowering effect and safety profile of viscocanalostomy procedure without external manipulations. I think the comparative study demonstrates the Table 1. The number of patients in each group in the 3-year follow-up.
Number of Patients (%) Follow-up
Trabeculectomy Group (n Z 25)
Viscocanalostomy Group (n Z 25)
6 months 1 year 2 years 3 years
5 (20) 8 (32) 8 (32) 4 (16)
4 (16) 10 (40) 6 (24) 5 (20)
J CATARACT REFRACT SURG - VOL 31, OCTOBER 2005
REFERENCES 1. Atchison DA. Pseudoaccommodation with forward movement of IOLs [letter]. J Cataract Refract Surg 2005; 31:11 2. Huber C. Myopic astigmatism as a substitute for accommodation in pseudophakia. Doc Ophthalmol 1981; 52:123–178 3. Donders FC. On the anomalies of accommodation and refraction of the eye; translated from the author’s manuscript by WD Moore. London, New Sydenham Society, 1864 4. Johnson L. A new theory of accommodation. Arch Ophthalmol (old series) 1924; 53:426–430 5. Coleman DL. Unified model for accommodative mechanism. Am J Ophthalmol 1970; 69:1063–1079 6. Coleman DJ. On the hydraulic suspension theory of accommodation. Trans Am Soc Ophthalmol 1986; 84:846–868 7. Thornton SP. Lens implantation with restored accommodation. Curr Canadian Ophthalmic Pract 1986; 4:60, 62, 82 8. Thornton SP, inventor; Eye Technology, Inc., assignee. Intraocular lens for capsular bag implantation. US patent 4 718 904. January 12, 1998 9. Thornton SP. Anterior ciliary sclerotomy with tissue barriers; the scleral approach to presbyopia treatment. Highlights Ophthalmol 2005; 33 (1): 19–20 10. Nawa Y, Ueda T, Nakatsuka M, et al. Accommodation obtained per 1.0 mm forward movement of a posterior chamber intraocular lens. J Cataract Refract Surg 2003; 29:2069–2072 11. Rana A, Milller D, Magnante P. Understanding the accommodating intraocular lens. J Cataract Refract Surg 2003; 29:2284–2287
Trabeculectomy versus viscocanalostomy for primary open-angle glaucoma 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 Z .2281 [Figure 2]), qualified success (P Z.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?
1852
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 REFERENCE 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
Reply: I appreciate the comments by Ahmed; however, I would like to clarify some points. First, we concluded that ‘‘[p]rimary trabeculectomy lowered IOP more than viscocanalostomy in primary open angle glaucoma patients.’’ From Table 2, which shows the mean postoperative IOP values, it is clear that the mean IOP was lower in the trabeculectomy group than in the viscocanalostomy group: P Z .03 at 1 day, P Z.002 at 1 week, P Z .005 at 3 months, and P Z .027 at 1 year. We all agree that the groups did not show a statistically significant difference in terms of surgical success criteria, and we did not conclude that the trabeculectomy group achieved a statistically significant surgical success rate compared with the rate in the viscocanalostomy group in the Discussion. We stated that it is difficult to compare intermediate and long-term follow-up studies because the success criteria are not uniform and also that the mean number of antiglaucoma medications was significantly lower in the trabeculectomy group (P Z .004). Table 1 shows the detailed number of follow-ups in our study group. The question of why we did not perform laser goniopuncture in the viscocanalostomy group is explained in the Discussion. The study was to compare the IOP-lowering effect and safety profile of viscocanalostomy procedure without external manipulations. I think the comparative study demonstrates the Table 1. The number of patients in each group in the 3-year follow-up.
Number of Patients (%) Follow-up
Trabeculectomy Group (n Z 25)
Viscocanalostomy Group (n Z 25)
6 months 1 year 2 years 3 years
5 (20) 8 (32) 8 (32) 4 (16)
4 (16) 10 (40) 6 (24) 5 (20)
J CATARACT REFRACT SURG - VOL 31, OCTOBER 2005