Canaloplasty: new contender in glaucoma surgery arena

Key Points

Canaloplasty is a nonpenetrating procedure indicated for the treatment of primary open-angle glaucoma (POAG). It is performed under a scleral flap and involves uses of a flexible, 200-µm microcatheter with a lighted tip (iTrack 250 A, iScience Interventional) and Healon GV (Advanced Medical Optics) to viscodilate the canal. A tensioning suture (10-0 Prolene) is passed through the circumference of Schlemm's canal to maintain patency of the canal.

At the end of March 2008, 150 U.S. surgeons were trained in the procedure along with 70 international surgeons, and more than 1,500 procedures had been performed worldwide.

Dr. Lewis explained, "By obviating the need for a bleb in the early and late postoperative period, this procedure has many advantages over filtering surgery. Now it has reached the stage where surgeons have begun to innovate beyond the initial technique, and looking ahead, we can expect additional surgical tools will expand microcatheter clinical indications and treatment options for glaucoma surgery.

"The power of microcatheter-based drug delivery to the canal, trabecular meshwork, suprachoroidal space, and posterior segment makes it a particularly exciting and promising technique for all of ophthalmology," he added.

The goal of canaloplasty is to restore circumferential flow from Schlemm's canal to the collector channels via a nonpenetrating approach in order to achieve physiological control of IOP without bleb-related complications.

Dr. Lewis outlined four lines of proof of its function:

"There has been demonstration of viscodilation of the canal and outflow system, stretching of the trabecular meshwork, and increased aqueous flow into the outflow system. However, the greatest evidence is derived from the prospective clinical trial," he said.

The clinical study enrolled 168 patients with POAG and IOP >21 mm Hg. Patients with more than two laser trabeculoplasties or secondary glaucoma were excluded.

Recently published clinical results show that at baseline, mean IOP was 23.9 mm Hg and patients were using a mean of 1.9 medications. At 24 months, the mean IOP was reduced by 36% to 15.2 mm Hg with patients taking an average of 0.6 medications.

The safety profile was favorable, but complications occurred. There was evidence of microscopic blood in the canal or a small amount in the anterior chamber. However, the incidence of gross hyphema was only 2%. Other complications included detachment of Descemet's membrane in 3% of eyes and a 5% incidence of elevated IOP.

"Importantly, only 6% of eyes had an inadvertent bleb at 18 months and in only 4% was it necessary to convert to trabeculectomy or placement of a drainage device. In contrast to trabeculectomy, there were no cases of flat or shallow anterior chamber, infection, wound leak, or choroidal effusion," Dr. Lewis said.

Patients who would be considered particularly good candidates for canaloplasty with tensioning suture placement are those at high risk for trabeculectomy failure or in whom there is increased concern about further loss of vision. Examples include individuals with significant ocular surface disease or a failed trabeculectomy in the fellow eye as well as those with high myopia who are at risk for maculopathy, patients with existing advanced glaucoma damage, and individuals taking immunosuppressant treatment or anticoagulants, or who have diabetes.