Canaloplasty providing durable IOP control at 18 months

January 15, 2008
Cheryl Guttman

Canaloplasty is being evaluated in a prospective study that enrolled 94 patients who were candidates for glaucoma surgery. The procedure was performed successfully in 74 patients (79%). Mean follow-up for the group is about 12 months, and more than half of the patients have been followed to 18 months. The results show well-controlled IOP and minimal complications.

Key Points

At the annual meeting of the American Academy of Ophthalmology, Dr. Lewis reported on an ongoing international, multicenter study evaluating the nonpenetrating approach to glaucoma surgery that was first introduced in 2005. Canaloplasty aims to restore physiologic IOP without dependence on a bleb by re-establishing circumferential flow from Schlemm's canal to the collector outflow channels. It involves a standard nonpenetrating dissection to expose Schlemm's canal and circumferential viscodilation of the canal, using a flexible, 200-µm microcatheter with a lighted tip (iTrack 250A, iScience Interventional) to inject an ophthalmic viscoelastic device (Healon GV, Advanced Medical Optics). Then, a trabecular tensioning suture of 10-0 polypropylene is placed to maintain patency of the canal.

The inclusion criteria for the canaloplasty study required patients to have an IOP of 21 mm Hg or higher recorded within 60 days prior to surgery and a diagnosis of OAG. Patients with any previous angle surgery, patients who had undergone more than two laser trabeculoplasty procedures, or those with closed or secondary OAG were ineligible.

Ninety-four patients were enrolled, and at baseline, they had a mean IOP of 24.7 mm Hg and were using an average of 1.9 medications. Complete circumferential catheterization of the canal and successful suture placement were accomplished in 74 eyes, and outcomes analyses were performed using data from this cohort.

All 74 eyes were seen at 3 months, and mean IOP was reduced to 16.5 mm Hg while patients were using on average only 0.4 glaucoma medications. Among 59 patients seen at 12 months, mean IOP was 15.3 mm Hg and mean number of medications used was 0.6. At 18 months, 38 evaluated patients had a mean IOP of 14.8 mm Hg with use of an average of 0.6 medications per patient.

Among the 94 eyes enrolled, 20 underwent canaloplasty combined with phacoemulsification. IOP control was even more favorable after combined surgery in this subset. Among 16 eyes seen at 3 months after combined surgery, mean IOP was 14.4 mm Hg, and the average number of medications used per patient was 0.1. Eight eyes were seen at 18 months, and they had a mean IOP of 14.0 mm Hg while using an average of 0.2 medications.

"The greater IOP lowering in patients undergoing cataract surgery also occurs with filtering surgery. As in trabeculectomy, it may be that providing greater anterior chamber depth and perhaps the effect of cataract surgery on the trabecular meshwork enhance the effect of the canaloplasty," Dr. Lewis said.

The anterior angle and Schlemm's canal were imaged with high-resolution ultrasound biomicroscopy, and those studies were used to grade the degree of trabecular distention achieved with placement of the tensioning suture. Distention was graded on a scale of 0 (no distention) to 3 (maximum distention) using reference images. IOP results were analyzed for eyes undergoing canaloplasty only if they had successful suture placement, and they were divided into two groups, one composed of eyes with minimal or no trabecular distention (n = 23) and another with measurable trabecular distention (n = 22). Both groups had a mean baseline IOP of 24.2 mm Hg.