Spotlight on Technology & Technique

Canaloplasy; an advancement in non-penetrating glaucoma surgery

spotlight on technology & technique
Canaloplasty:A Promising New Extensionto Non-Penetrating Surgery
By Leslie Goldberg, Assistant Editor

Canaloplasty, a recent advancement in non-penetrating glaucoma surgery, is designed to improve the aqueous circulation through the trabecular outflow process, according to John R. Kearney, M.D., founder and director of The Cataract Care Center, N.Y. The canaloplasty procedure attempts to enhance aqueous outflow without creating a bleb. Pilot studies and early multisite studies have achieved promising results, says Dr. Kearney.  

Dr. Kearney, an early investigator of the viscocanalostomy procedure that he learned from its originator, Robert Stegmann, M.D., of Pretoria, South Africa, was also one of the first surgeons to dilate 360° of Schlemm's canal using a flexible microcannula. In this dilation study, a significant reduction in postoperative IOP was obtained by circumferential dilation. During this study, Dr. Kearney introduced the dilation procedure to Dr. Stegmann, who in turn added the placement of an intracanalicular tension suture, creating the canaloplasty procedure.

Figure 1. Introduction of the microcatheter into Schlemm's canal.

What is a Canaloplasty?

A canaloplasty is a 360° viscodilation of the Schlemm's canal with an illuminated beacon-tipped microcatheter. The microcatheter is used to place an intracanalicular suture that cinches and stretches the trabecular meshwork inwards while permanently opening Schlemm's canal, explains Dr. Kearney. The difference between a viscocanalostomy and a canaloplasty is that the canaloplasty aims at opening the entire length of the canal, not just one section of it. The procedure restores the natural drainage of fluid from the eye, thus reducing IOP.

"Nearly 90% of patients do not require glaucoma drops after the surgery," says Dr. Kearney. "It has been evaluated on primary open-angle glaucoma, pseudoexfoliative glaucoma and pigmentary glaucoma. Theoretically, it should work on most types of glaucoma, as does viscocanalostomy, even after drops, pills, laser and other types of glaucoma surgery have failed." Complications are far less frequent and less severe than in most other types of glaucoma surgery, says Dr. Kearney.

The canaloplasty begins similar to a viscocanalostomy. As in viscocanalostomy, parabolic superficial and deep scleral flaps are produced. (The superficial flap should be between 200-250 microns thick). The deep flap is dissected to the plane of Schlemm's canal and the sides of the deep flap are then dissected forward into the cornea. Reflection of the inner flap unroofs Schlemm's canal, creating a trough leading to two entrances into Schlemm's canal (surgical ostia). Further reflection of the flap creates an intact window in Descemet's membrane, and gentle pressure at the level of Schwalbe's line, using a cellulose sponge, extends the window. Aqueous humor diffuses through this window into a subscleral space (lake). 

The microcannula is introduced into the entrance of Schlemm's canal, and advanced 360° while high-viscosity sodium hyaluronate is gently injected into the canal to force open the entire length
(Figure 1). A 10-0 suture is tied to the microcannula and withdrawn through the canal. The suture is tied together as a pursestring to apply tension on the trabecular meshwork and open the canal (Figure 2). A double-suture technique, adopted by Drs. Stegmann and Kearney in 2005, further reduces the likelihood of closure through scar formation and pressure rise, especially if one suture loosens.

The deeper scleral flap is excised (deep sclerectomy) and the superficial flap is sutured securely. Tight closure is mandatory to prevent bleb formation. High-viscosity sodium hyaluronate is then injected into the subscleral lake to act as a physical barrier to fibrinogen migration postoperatively.

"Making a parabolic superficial flap leaves no sharp corners as in a rectangle, square or triangle flap," says Dr. Kearney. "These corners tend to leak, which is essential in trabeculectomies. A curved edge is easier to close tightly and prevent leakage. This is desirable in viscocanalostomy and canaloplasty, as you want the flow of aqueous to channel into Schlemm's canal and exit the eye via the collector channels, i.e., internal filtration as opposed to external filtration."

Figure 2. A 10-0 polypropylene suture being tied around the end of the microcatheter.

iScience Surgical's Microcannula

The iScience Surgical (Menlo Park, Calif.) Ophthalmic Microcannula (OM) has become an important piece of equipment used in performing this procedure. iScience Surgical's OM is used to insufflate Schlemm's canal with viscoelastic as part of the canaloplasty technique and serves as a means for placing the drawstring suture to open Schlemm's canal, said Dr. Stegmann in an interview with Eurotimes.

The microcannula has a diameter of 200 microns and an atraumatic tip. An LED light source shone through an optical fiber illuminates the catheter tip, which also contains a lumen for the injection of high-viscosity sodium hyaluronate. The surgeon can see the pulsed red flash at the catheter's tip and knows where the catheter is at all times.

Additionally, a new high-resolution ultrasound system, also produced by iScience Surgical, provides accurate localization of Schlemm's canal and can also provide confirmation of the success of the procedure.

"iScience Surgical's microcannula allows surgeons to dilate Schlemm's canal 360°. Previously, surgeons were only able to dilate 120° of the canal. This added dilation allows the surgeon to potentially allow flow of aqueous to pass through the entire trabecular meshwork, where the greatest resistance to outflow is believed to be located." notes Dr. Kearney.

Criteria for Success

"I believe that the procedure is a success if the IOP is lowered sufficiently to prevent further optic nerve damage without the use of pressure-lowering medications," says Dr. Kearney. "I don't believe in just a percentage drop in IOP, but rather to a target range. We are now seeing pressure drops to the low-to-mid teens, lower in some cases, but the actual statistical results are being compiled for an evidence-based, peer-reviewed article."