OBJECTIVE: To study the learning risk of a new surgical technique, the deep sclerectomy (DS), which may be complicated with a perforation of the trabeculodescemetic membrane. To do so, we compared the results and the complications of patients who underwent DS transformed in trabeculectomy (DSt) and those of patients who underwent trabeculectomy (TE). MATERIALS AND METHODS: Between june 1994 and june 1996, we performed 234 DS, 19 of them had to be transformed into a TE, because of a perforation of the trabeculodescemetic membrane during the deep sclerocorneal dissection. Two matched groups of patients were prospectively followed, one group including 19 DSt and a control group including 19 TE. RESULTS: The IOP decrease on the first postoperative day was greater in the DSt-group compared to the TE-group (2.32 +/- 3.89 vs 6.73 +/- 4.31, p = 0.004). Scleral perforations occurred mainly during the learning phase of this new surgical technique. Postoperative complications were similar in both groups, except for hypotony and hyphema which were more frequent in the DSt-group (hypotony: 90% vs 37%, p = 0.0019; hyphema: 68% vs 16%, p = 0.017). The long term success rate with or without medication were comparable in both groups. CONCLUSION: This study shows that, when a DS is complicated with a perforation of the trabeculodescemetic membrane, the long term success rate of the surgery is similar to that of trabeculectomy. However, immediate postoperative complications such as hypotony and hyphema are increased. These results should encourage surgeons to learn this new non perforating filtration surgery.