Canaloplasty: Where Does it Fit in the Glaucoma Treatment Paradigm?

The causes of glaucoma are not completely understood. However, we do know that buildup of aqueous in the anterior chamber causes increased pressure that damages the optic nerve fibers. Once this damage is done, there is no way to repair it or restore lost sight. Canaloplasty is a blebindependent procedure that addresses the natural outflow pathways of the eye and offers a good risk profile and rapid postoperative recovery. The combination of high efficacy and an excellent safety profile makes it a choice treatment for many glaucoma patients.

One of the benefits of canaloplasty is rapid visual recovery. This makes it favorable for combining with cataract surgery, and together the procedures have a synergistic effect that tends to lower intraocular pressure (IOP) even more than canaloplasty alone. In the first month after surgery, there is some residual astigmatism that is likely due to the closure of the flap, but the patient generally returns to preoperative visual acuity fairly quickly.

WHEN TO USE

Canaloplasty evolved from viscocanalostomy, and it addresses failures of that earlier procedure such as recollapse of Schlemm canal and closure of the ostia.^1,2 By dilating the entire Schlemm canal with the iTrack microcatheter (iScience Interventional; Figure 1) and permanently stretching the inner wall with a tensioning suture, canaloplasty addresses atrophy and other pathology in all three sites of the outflow system: the trabecular meshwork, Schlemm canal, and the collector channels. Most patients with open-angle glaucoma and some with narrow-angle glaucoma are good candidates for canaloplasty.

In a recent study,³ at 3 years postoperative, the mean intraocular pressure (IOP) in patients who underwent canaloplasty was 15.5 ±3.5 mm Hg compared with baseline IOP of 23.5 ±4.5 mm Hg.The mean IOP in eyes that underwent combined cataract and canaloplasty was 13.6 ±3.6 mm Hg compared with baseline IOP of 23.5 ±5.2 mm Hg. The nonrandomized multicenter study included 157 eyes with open-angle glaucoma that were operated on by surgeons who had no previous experience with nonpenetrating surgery, although some had performed viscocanalostomy.

Most patients also see a significant reduction in the number of glaucoma medications required. In the same 3-year study, patients were taking a mean of 1.8 ±0.9 medications at baseline but only 0.8 ±0.9 at completion of the study. Among the patients who underwent combined phacoemulsification and canaloplasty, the mean number of medications at baseline also decreased (1.5 ±1.0 vs 0.3 ±0.5, respectively).

Lack of compliance with glaucoma medications is a well-known and documented drawback of medical treatment of glaucoma.⁴ Patients who have declared difficulty or distaste in purchasing or instilling their glaucoma medications may be good candidates for canaloplasty.

SAFETY PROFILE

The low risk profile of canaloplasty makes it an acceptable option for patients with mild to moderate glaucoma who have difficulty with their topical ophthalmic medications. The same 3-year study showed excellent short- and long-term safety profiles, with late postoperative complications including cataract (12.7%), transient IOP elevation (6.4%), and partial suture extrusion through the trabecular meshwork (0.6%). The absence of typical severe complications of glaucoma surgery such as hypotony, choroidal detachment, and blebitis makes for easy postoperative management and expands the range of glaucoma patients for whom canaloplasty is an acceptable option. Most patients are given a postoperative regimen similar to that for cataract surgery, with a topical antibiotic three to four times daily and follow-up exams once a week after surgery. The patient benefits from rapid visual recovery and few side effects after surgery.

TIPS FOR MASTERING A NEW TECHNIQUE

For surgeons who have performed viscocanalostomy, canaloplasty uses the same approach, with dissection of superficial and deep scleral flaps. However, these surgeons will have to learn two new steps: 360° cannulation with viscodilation and placing of the suture stent. As with all new procedures, there is a learning curve. Surgeons should be persistent and not get discouraged. The first cases are always a bit difficult. These five tips can help shorten the curve.

Create a large Descemet window. This helps the surgeon insert the microcatheter during surgery and serves as a back-up to allow laser goniopuncture postoperatively.

Use high magnification. Locating Schlemm canal is the most difficult part of this nonpenetrating surgery, so using high magnification is recommended. This increases familiarity and allows the surgeon to see the fibers of the remaining sclera during deep flap dissection leading to Schlemm canal.

Perform cannulation gently. Additionally, the surgeon must observe the blinking light at the tip of the microcatheter at all times as an indicator of when to dilate and to ensure that the probe is not moving into the suprachoroidal space, the anterior chamber, or a large collector channel.

Get a feel for the amount of tension required. The tensioning suture is placed in the canal, and then both ends of the thread are pulled equally to close the circle (Figure 2). Physicians will get a feel for the tension required with practice, and they should not be afraid of this step.

Close the flap tightly. It is recommended that surgeons close the flap tightly to avoid any bleb filtration (Figure 3). Canaloplasty was conceived as a bleb-independent procedure, and that is what eliminates a lot of the postoperative complications, including hypotony and bleb-related problems. The only case in which I recommend creating some subconjunctival filtration by not suturing the flap tightly is if the eye has undergone previous surgery that prevents the surgeon from passing the microcatheter around Schlemm canal. In this instance, I dilate the canal as much as I can with an ophthalmic viscosurgical device and suture the flap more loosely to allow external filtration.

CONCLUSION

Canaloplasty appears to be a safe and effective procedure with a low risk profile, requiring minimal postoperative management and providing excellent IOP control. It meets all of the patient and physician goals of a glaucoma treatment, in that it is effective at controlling IOP while preserving vision and having a minimal impact on patient lifestyle, and it is my treatment of choice for most of my open-angle glaucoma patients. Additionally, combining canaloplasty with cataract surgery can create a synergistic effect, lowering IOP even more than canaloplasty alone.

Matthias C. Grieshaber, MD, FEBO, FMHOphth, is an Assistant Professor at the University Basel, Switzerland. Dr. Grieshaber states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +41 612658781; e-mail: mgrieshaber@uhbs.ch.

1. Stegmann R, Pienaar A, Grieshaber MC. Schlemm’s canal surgery: restoring physiological aqueous outflow. In: Grieshaber MC, Orgul S, Flammer J, eds. Glaucoma Therapy — State of the Art. Basel: Association for Continuing Education in Ophthalmology; 2009.
2. Grieshaber MC, Pienaar A, Olivier J, Stegmann R. Canaloplasty in primary open-angle glaucoma: long-term outcome. Br J Ophthalmol. 2010;94(11):1478-1482.
3. Lewis RA, von Wolff K, Tetz M, et al. Canaloplasty: three-year results of circumferential viscodilation and tensioning of Schlemm canal using a microcatheter to treat open-angle glaucoma. J Cataract Refract Surg. 2011;37(4):682-690.
4. Nordstrom BL, Friedman DS, Mozaffari E, Quigley HA, Walker AM. Persistence and adherence with topical glaucoma therapy. Am J Ophthalmol. 2005;140(4):598-606.