Access to Schlemm's canal for canaloplasty: an intra-individual comparison of two dissection techniques

Purpose: To compare a modified incision technique with classic scleral flap dissection for canaloplasty with canal expander regarding efficacy and safety. Methods: In a prospective randomized pilot study of 32 eyes of 16 patients with primary open-angle glaucoma, access to Schlemm's canal was created by deep lamellar dissection (scleral flap excision, group 1) or by vertical cut-down incision (group 2). Following canal opening and viscodilation with microcannula and sodium hyaluronate, two Stegmann Canal Expanders were implanted, and the scleral flap or vertical incision, respectively, was closed watertight. Results: Mean preoperative intraocular pressure (IOP) was 34.9 mmHg ± 6.7 [standard deviation (SD)] in group 1 and 33.8 mmHg ± 7.7 (SD) in group 2 (p = 0.66); mean postoperative IOP without medications was 14.3 mmHg ± 2.9 (SD) in group 1 and 14.8 mmHg ± 5.2 (SD) in group 2 at 1 month (p = 0.76), and 14.4 mmHg ± 1.9 (SD) in group 1 and 16.8 mmHg ± 3.1 (SD) in group 2 at 12 months (p = 0.01). Overall, there was a significant preoperative–postoperative IOP difference between groups (19.4 mmHg ± 10.1, group 1; 16.6 mmHg ± 8.9, group 2; p = 0.02). Surgery type had a significant effect when adjusted for preoperative IOP, cup–disc ratio, eye side, follow-up number and surgery type (p < 0.01, anova). No filtering bleb was observed in either group. Intra- and postoperative complications were rare and included peripheral Descemet's membrane detachment (3), microhyphema (2) and cannulation into the anterior chamber (1). Conclusions: In this intra-individual comparative study of ab externo canaloplasty with the canal expander, IOP reduction was substantial in both groups and slightly greater in the group with deep scleral flap excision. Additional IOP reduction by transscleral drainage through the Descemet's membrane window and intrascleral lake is suggested.