Non-penetrating Schlemm's canaloplasty found safe for intraocular pressure control

Stanford, CA-Results of a retrospective chart review study show that non-penetrating Schlemm's canaloplasty (NPSC) can be as effective as trabeculectomy with mitomycin-C (MMC) for providing IOP control in eyes with open-angle glaucoma, but may be a potentially safer option because it avoids a bleb, said Diamond Y. Tam, MD.

NPSC involves non-penetrating dissection to expose Schlemm's canal, circumferential viscodilation of the canal using a flexible microcatheter (iTrack 250A, iScience Interventional), and placement of a Schlemm's canal tensioning suture.

The need for adjunctive procedures to achieve IOP control and overall complication rates also were similar in the two groups. However, sight-threatening complications were more common after trabeculectomy, and NPSC also had an advantage over trabeculectomy in terms of faster return of best-corrected visual acuity (BCVA) and a better BCVA outcome at 1 year.

"Trabeculectomy was first described in 1968 and is still considered by many to be the gold standard in terms of surgical procedures for IOP control," Dr. Tam said. "However, it has a long list of short- and long-term risks-including serious complications such as blebitis, endophthalmitis, and overfiltration hypotony-that has led to the development of alternative surgical techniques.

"Canaloplasty is a relatively new, non-penetrating procedure that aims to restore outflow through the conventional pathway," he added. "It also aims to avoid a subconjunctival bleb, and therefore also potentially may be safer than trabeculectomy, reducing the incidence of bleb-related complications."

The two patient populations were similar with respect to preoperative disease severity based on mean visual field values (mean deviation, pattern standard deviation) and cup-to-disc ratios. Mean IOP also was similar in the NPSC and trabeculectomy groups preoperatively, 26.4 ± 6.5 and 26.8 ± 8.1 mm Hg, respectively, and was significantly reduced in both groups at 1 year, 13.4 ± 2.7 mm Hg (–49%) and 12.3 ± 3.5 mm Hg (–54%), respectively, with no significant difference between groups.

The mean number of IOP-lowering medications used was 3.6 in both groups preoperatively and was reduced to 0.6 and 0.7 in the NPSC and trabeculectomy groups, respectively, at 1 year. The slight difference in 1-year values was not statistically significant, and there were no significant differences between the two groups in mean medication use at earlier timepoints.

Mean BCVA worsened after each procedure but returned to baseline by 3 months postoperatively in each group. However, there was a trend for earlier BCVA recovery after canaloplasty, and at 1 year, mean BCVA was significantly better in eyes that underwent canaloplasty.

Safety review

The safety review showed each procedure had a unique profile of complications, but rates of some potentially serious complications were significantly higher after trabeculectomy compared with NPSC.

Choroidal effusion and transient hypotony (IOP < 6 mm Hg for at least two visits that resolved spontaneously) occurred in 14 (28%) and 13 (26%) eyes, respectively, after trabeculectomy, but each of these complications occurred in only one (2%) eye that had NPSC. A shallow/flat anterior chamber was seen only after trabeculectomy (16%) as were bleb-related complications, including fibrosis (12%), wound leak (10%), and encapsulation (8%), and the rate of loss of more than 2 lines of Snellen visual acuity also was significantly higher in the trabeculectomy versus NPSC group (16% versus 2%).

Localized Descemet's detachment (4%) and angle closure with iris bombe (2%) were unique to NPSC.

Adjunctive postoperative procedures also varied by type of surgery. Laser goniopuncture was performed in 17 (34%) eyes in the NPSC group versus in one (2%) eye after trabeculectomy, and iris sweep also was performed significantly more often after NPSC compared with trabeculectomy (10% versus 2%). However, compared with NPSC, trabeculectomy was associated with significantly higher rates of laser suture lysis (26% versus 2%), bleb needling (12% versus 2%), and anterior chamber reformation with ophthalmic viscosurgical device (16% versus 2%).

FYI

Diamond Y. Tam, MDE-mail: diamondtam@gmail.com

Dr. Tam had no relevant financial interests at the time of the study presentation but is now a consultant for iScience Interventional. Dr. Ahmed also is a consultant for iScience Interventional.