Canaloplasty: A Thorough Overview

This innovative procedure advances glaucoma treatment.

BY RICHARD A. LEWIS, M.D.

Canaloplasty is a recent advancement in non-penetrating glaucoma surgery that enhances aqueous outflow without forming a bleb. The major difference between a standard viscocanalostomy and canaloplasty is that the canaloplasty allows for a full circumferential opening of Schlemm's canal, not just a section of it. In this article I will provide a complete overview of this innovative procedure.

I have described canaloplasty as a minimally invasive, site-specific interventional ophthalmology treatment that is made possible by the development of the iTrack microcatheter (iScience Interventional, Menlo Park, Calif.). This illuminated beacon-tipped microcatheter facilitates a 360° viscodilation of the Schlemm's canal and is used to place an intracanalicular suture that cinches the trabecular meshwork inwards while permanently opening Schlemm's canal.

The microcatheter has a diameter of 200 μm and an atraumatic tip. An LED light source shone through an optical fiber illuminates the tip, providing a visible flashing light as a reference point during interventional ophthalmic procedures. This also contains a lumen for the injection of high-viscosity sodium hyaluronate. The surgeon can visualize the pulsed red flash at the catheter's tip and thus has visual contact with that tip at all times.

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

The Technique: Step by Step

Canaloplasty begins very similarly to viscocanalostomy, where parabolic superficial and deep scleral flaps are produced. The superficial flap should be between 200 μm to 250 μm. The deep flap is dissected down between 300 μm and 400 μm to a level that is just superficial to the choroids. This creates a scleral lake. After the deep flap is formed, dissect forward to reveal the Schlemm's canal and create a Descemet's window.

Next, gently insufflate the surgically created ostia with a high-viscosity viscoelastic. This will serve as a lubricant to allow the safe insertion of the microcatheter. Once the microcatheter is passed the full 360° through Schlemm's canal and emerges at the operative site, attach two 10/0 prolene sutures to the catheter, which can be drawn back through the canal. After withdrawing the catheter, tie off the ends of the sutures with a special slipknot to create a mild amount of tension. Such tension from this "purse string" will pull the trabecular meshwork away from the outer wall and open the canal.

Canaloplasty provides a full opening of Schlemm's canal.

A double-suture technique, adopted by Robert Stegmann, M.D., and John Kearney, M.D., 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. It is imperative to ensure tight closure to prevent bleb formation. High-viscosity sodium hyaluronate is then infected into the subscleral lake to act as a physical barrier to fibrinogen migration postoperatively.

In developing the superficial and deep scleral flaps, the importance of the parabolic shape is that it leaves no sharp corners as in a rectangle or triangle flap where the corners may leak. Such edges are desirable in trabeculectomies. For canaloplasty a curved edge is more facile to close tightly and prevent leakage.

This is desirable in both the viscocanalostomy and canaloplasty procedures as you want the flow of aqueous into Schlemm's canal and through the eye via the collector channels. This is an example of internal filtration as opposed to external filtration.

Results Being Achieved

The value of canaloplasty is the combination of efficacy and lack of side effects as compared with other glaucoma procedures, especially trabeculectomy. The 2-year analysis revealed IOP reduction from 23.9 mm Hg (and 1.9 meds) to 15.5 mm Hg (and 0.5 meds). Equally important, there were no cases of flat chambers, endophthalmitis or wound leaks. These results make canaloplasty a desirable option for any glaucoma surgeon because it saves us time in postop follow up and we find that we have happier patients. In addition to being good for your practice, this procedure saves patients time because there are few complications to treat. It also saves them money by reducing the amount of medication they take.

Canaloplasty is indicated in open-angle glaucoma. I have found it an especially valuable procedure for contact lens wearers, eyes with significant ocular surface disease and those individuals with a failed trabeculectomy in the other eye. It is also a very useful procedure in patients with high myopia, immuno-supression therapy and ocular hypotony in whom the fellow eye developed hypotony. Some of my colleagues also view it as the ideal procedure for glaucoma patients with corneal implants, as it causes the least disruption to the cornea, reducing the risk of rejection. Based on my experience with the procedure, canaloplasty has an important place in a glaucoma practice because it is safe and effective for some difficult patient cases. Unfortunately, many surgeons shy away from adopting canaloplasty because of its rumored learning curve.

Catheter tip in Schlemm's canal, being monitored by beacon of light.

I contend that the accusations that canaloplasty is "too difficult and too time consuming" is not true. After the initial didactic course and lab, an iScience clinical specialist is with you in your OR throughout the initial learning curve (approximately 5 to 10 cases). I would compare canaloplasty's learning curve as being roughly similar to the time and experience needed to become proficient in performing phacoemulsification. With experience, canaloplasty becomes a 30 to 40 minute procedure. The additional time as compared to a trabeculectomy is offset by the simplified postop management process. I believe that when more surgeons come to believe that the value of becoming proficient in performing canaloplasty is much greater than the effort it takes to learn it, the popularity of this procedure will greatly increase.

Canaloplasty With Phaco

Recent experience has broadened the scope of canaloplasty even more, by showing that it is effective in conjunction with phaco. In just 2 short years, this procedure has proven that it has a place in glaucoma management and is beneficial to patients and doctors. Data continues to show that canaloplasty reduces the amount of medication taken and has few postop complications, something that we have been searching for since trabeculectomy became the standard of care for glaucoma patients. I have found great success using this procedure and am confident that once other surgeons get over their fear of the learning curve, they — and their patients — will be quite happy with the results. OM

Richard A. Lewis, M.D., is the former director of glaucoma at the University of California, Davis. In addition to his clinical practice located in Sacramento, Calif., Dr. Lewis is actively involved in clinical research in national and international trials in glaucoma therapy. He is past president of the American Glaucoma Society and served on the steering committee of the Association of International Glaucoma Society. He is co-founder of Sacramento's Capital City Surgery Center. Dr. Lewis has published many articles and book chapters on glaucoma, ophthalmic surgery and ophthalmic pharmacology. He is co-author of the book, Curbsides in Glaucoma. His video and computer productions include Tonometry, a video and CD-ROM published by the American Academy of Ophthalmology. He has received the American Academy of Ophthalmology Honor and Senior Honor Awards for his contributions in teaching and leadership and for initiating the AAO Subspecialty Day meeting. He has been an investigator for, and also receives research support from, IScience.