Canaloplasty a viable option after mini shunt failure

The anterior chamber angle must be open for continued egress of aqueous humor from the anterior chamber to the collector channels.

Thomas John

Surgical management of glaucoma can be challenging to the practicing ophthalmologist. While trabeculectomy has been the gold standard for glaucoma management, nonpenetrating procedures are continuing to gain popularity among those who surgically treat glaucoma. One such nonpenetrating procedure, canaloplasty, usually eliminates the problems associated with a bleb and hypotony-related issues such as maculopathy.

Another surgical procedure that is also gaining in popularity is the Ex-PRESS mini glaucoma shunt (Alcon). When an Ex-PRESS shunt fails over time, the choices include repeat Ex-PRESS shunt, use of another commercially available shunt or a trabeculectomy. An alternative procedure that may be considered in such a case is canaloplasty, as long as the anterior chamber angle is open for continued egress of aqueous humor from the anterior chamber to the collector channels. A failed Ex-PRESS shunt is usually not a contraindication for subsequent canaloplasty.

In this column, I describe the surgical steps of performing a canaloplasty after a failed Ex-PRESS shunt in patients with open-angle glaucoma.

Surgical technique

The type of anesthesia is based on surgeon preference and may vary from subconjunctival anesthesia with monitored anesthesia care to general anesthesia. A corneal 6-0 Vicryl suture is used to rotate the globe inferiorly and to tuck the dissected superficial scleral flap to provide optimal surgical exposure. The sclera is exposed by blunt and sharp dissection, and hemostasis is achieved using a disposable cautery. No mitomycin C is used in this procedure.

A Mastel Precision parabolic marker is used to mark the sclera (Figure 1). The superficial flap incision is made with the Mastel canaloplasty diamond blade set at a depth of 350 µm, and the scleral mark is used as a guide to make the incision. The superficial scleral flap is dissected with the diamond blade fully extended (Figure 2). The scleral flap incision is then extended to at least 1 mm onto the peripheral clear cornea (Figure 3). This corneal extension allows for fashioning the trabeculo-Descemet’s membrane window subsequently during the procedure.

The superficial scleral flap is dissected onto the clear cornea using the Mastel canaloplasty diamond blade (Figure 4). The deep flap is created using the diamond blade set at 200 µm (Figure 5), which is usually just above the choroid. It is important to maintain the surgical plane of tissue dissection.

Figure 1. A Mastel parabolic marker is used to mark the sclera and helps guide in creating the superficial scleral flap. This superficial flap incision is made with the Mastel canaloplasty diamond blade set at a depth of 350 µm.

Figure 2. The superficial scleral flap is dissected with the diamond blade fully extended. Images: John T

Figure 3. The scleral flap incision is extended onto the peripheral clear cornea.

Figure 4. The superficial scleral flap is dissected onto the clear cornea using the Mastel canaloplasty diamond blade.

Figure 5. The deep flap is created using the diamond blade set at 200 µm.

Figure 6. Extension of the deep flap at 200-µm depth unroofs Schlemm’s canal, and egress of the aqueous humor from the anterior chamber is clearly visible.

Figure 7. The lateral extension of the flap is made using the diamond blade.

Figure 8. Catheterizing Schlemm’s canal.

Figure 9. The fiber optic catheter is held concentric to Schlemm’s canal during the catheterization, and progression of the catheter is clearly visible with the blinking red light at the tip. The catheter is passed 360° to exit the wound.

Figure 10. A 9-0 Prolene suture is tied to the tip of the iTrack catheter.

Prior to catheterization, viscoelastic is used to prime the catheter to ascertain patency. The fiber optic catheter is held concentric to Schlemm’s canal during the catheterization, and progression of the catheter is clearly visible with the blinking red light at its tip. The catheter is passed 360° to exit the superior surgical wound (Figure 9). The catheter usually passes beyond the region of the failed Ex-PRESS shunt.

Dimming the microscope light during catheterization optimizes the view of the catheter tip’s blinking red light. Avoid catheter misdirection into the suprachoroidal space or into the anterior chamber.

A 9-0 Prolene suture is tied to the tip of the iTrack catheter (iScience Interventional) (Figure 10). The iTrack catheter is then withdrawn, resulting in the stent being placed within Schlemm’s canal (Figure 11). At every 2 clock hours during catheter withdrawal, viscoelastic is injected to dilate Schlemm’s canal (Figure 11). The catheter’s location is identified by the red terminal light (Figure 12).

The Khan dissector facilitates the creation of the Descemet’s window after the eye is softened with a paracentesis (Figure 13). The Descemet’s window permits aqueous humor to percolate through and also provides a site through which a Nd:YAG goniopuncture may be performed postoperatively, if needed. Lowering the IOP decreases the risk of accidentally tearing the Descemet’s window. It also helps create a reverse blood reflux into Schlemm’s canal, which usually helps in the identification of the ostia of Schlemm’s canal through which the fiber optic catheter is subsequently passed.

Figure 11. Withdrawing the iTrack catheter results in the stent being placed within Schlemm’s canal. At every 2 clock hours during catheter withdrawal viscoelastic is injected to dilate Schlemm’s canal.

Figure 12. While retracting the catheter, the location of the catheter is identified by the red terminal light.

Figure 13. Creating Descemet’s window using the Khan dissector.

Figure 14. The margins of the deep flap are extended on either side using a Barnebey zip blade.

Figure 15. The deep flap is amputated at the base using Vannas scissors.

Figure 16. The suture stent is then tied to expand Schlemm’s canal.

Figure 17. The scleral lake is filled with Healon.

Figure 18. The superficial flap is closed tightly with 10-0 nylon sutures, and the conjunctiva is approximated and attached with interrupted 10-0 Vicryl sutures. The completed view of the procedure is seen on the right.

The margins of the deep flap are then extended on either side using a Barnebey zip blade (Figure 14). The deep flap is amputated at the base using Vannas scissors (Figure 15). The suture is gently pulled in either direction to “floss” Schlemm’s canal and is then tied (Figure 16) with adequate tension to expand Schlemm’s canal while avoiding excessive tension that may result in suture cheese-wiring through Schlemm’s canal.

The scleral lake is then filled with Healon (sodium hyaluronate, Abbott Medical Optics) (Figure 17). The superficial flap is closed tightly with one to three 10-0 nylon sutures (Figure 18). Tight scleral flap approximation prevents unwanted bleb formation postoperatively. Sterile balanced salt solution is injected into the anterior chamber, and the wound is checked for any leakage. The desired ending IOP is about 20 mm Hg. The conjunctiva is approximated and attached with interrupted 10-0 Vicryl sutures (Figure 18).

References:

• Ayyala RS, Chaudhry AL, Okogbaa CB, Zurakowski D. Comparison of surgical outcomes between canaloplasty and trabeculectomy at 12 months’ follow-up [published online ahead of print Aug. 18, 2011]. Ophthalmology. doi:10.1016/j.ophtha.2011.05.021.
• Grieshaber MC, Fraenkl S, Schoetzau A, Flammer J, Orgül S. Circumferential viscocanalostomy and suture canal distension (canaloplasty) for whites with open-angle glaucoma. J Glaucoma. 2011;20(5):298-302.
• Bull H, von Wolff K, Körber N, Tetz M. Three-year canaloplasty outcomes for the treatment of open-angle glaucoma: European study results. Graefes Arch Clin Exp Ophthalmol. 2011;249(10):1537-45.
• 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.

• Thomas John, MD, is a clinical associate professor at Loyola University at Chicago and is in private practice in Oak Brook, Tinley Park and Oak Lawn, Ill. He can be reached at 708-429-2223; fax: 708-429-2226; email: tjcornea@gmail.com.
• Disclosure: Dr. John has no relevant financial disclosures.