IIB Uveoscleral Outflow Procedures Traditional glaucoma surgical procedures such as trabeculectomy, although very effective in lowering the intraocular pressure (IOP), may be associated with numerous complications, including bleb leaks, cataracts, blebitis, endophthalmitis, and vision loss. Consequently, many glaucoma specialists seek a safer and less invasive procedure that delivers the same IOP-lowering benefits as trabeculectomy. Canaloplasty is a bleb-free procedure that works by restoring the natural ocular outflow system. Published evidence indicates that canaloplasty may be used across the glaucoma treatment spectrum, as it is both safe and effective, it reduces the need for medical therapy, and it entails minimal postoperative care. Perhaps unsurprisingly, canaloplasty is gradually becoming the go-to treatment for glaucoma specialists seeking a minimally invasive, maximally effective solution for open-angle glaucoma. A 61-year-old African-American woman presented to the glaucoma service after referral from a local optometrist who had been treating her for many years. She had a long-standing diagnosis of primary open-angle glaucoma (POAG) and high myopia, and was recently diagnosed with visually significant cataracts by the referring optometrist. Upon presentation, her best corrected visual acuity was 20/30 in the right eye and 20/50 in the left eye. Her current glasses were –14.25 +1.50 × 171 OD and –11.25 +1.50 × 040 OS. Subjective manifest refraction at our first visit was –14.00 +1.00 × 165 OD and –11.50 +1.50 × 044 OS. This yielded a visual acuity of 20/40 –2 OD and 20/60 OS. Goldman applanation tonometry was 24 mm Hg in both eyes. She was compliant with instilling latanoprost in both eyes at bedtime and dorzolamide/timolol in both eyes b.i.d. Central corneal thickness was 478 µm OD and 492 µm OS. Gonioscopy exhibited an open angle to 40 degrees, and a flat iris approach with 1+ pigmentation to the trabecular meshwork. There were a few iris processes intermittently throughout each angle; 2+ nuclear sclerosis with cortical changes and central vacuoles were also observed. The remaining anterior segment was unremarkable. Posterior examination demonstrated tilted optic nerves with temporal sloping. Cup-to-disk ratios were 0.8 in both eyes. Peripapillary atrophy was noted bilaterally. The maculae were flat without evidence of degeneration. No posterior staphyloma was identified. The remaining posterior segment examination was unremarkable. Ancillary testing included a Humphrey visual field, optical coherence tomography, and intraocular lens (IOL) calculations. The Humphrey visual field was reliable and demonstrated an early superior arcuate defect in the right eye and an early inferior arcuate defect in the left eye with superior nasal step changes. Optical coherence tomography demonstrated retinal nerve fiber layer thinning in both eyes. The superior and inferior nerve fiber layers were significantly thinned compared with age-matched controls. The patient underwent uncomplicated cataract extraction with IOL implantation followed by successful canaloplasty surgery in the right eye. Approximately 6 weeks later, the same procedure was completed successfully in the left eye. No complications were encountered. Postoperatively, the patient has done very well. She is no longer using ocular medication to control her IOP and her vision is 20/20 in both eyes with a minimal need for corrective lenses. Her IOP has remained in the mid-teen range, and she has been off medications since the time of surgery. Until relatively recently, treatment for POAG was restricted to medical therapy or traditional glaucoma surgeries such as aqueous shunts and trabeculectomy. Many physicians still regard trabeculectomy as the gold standard in glaucoma treatment because of its ability to effectively lower IOP and arrest disease progression, but it is also associated with numerous immediate and delayed postoperative complications.1–6 Additionally, although we know that suboptimal ocular outflow is a key factor in the development of glaucoma, trabeculectomy works by circumventing, rather than restoring, natural ocular outflow. In contrast, canaloplasty, a modification of viscocanalostomy, restores the physiological outflow pathways, thus lowering IOP both safely and effectively.7,8 Although canaloplasty is usually indicated for patients with POAG who have not undergone previous filtration surgery, growing evidence suggests it may also be considered in patients for whom other types of surgery have failed.9 As the above case presentation demonstrates and as clinical data from literature indicate, canaloplasty may also be safely combined with cataract surgery.10–12 Canaloplasty is a surgical procedure performed under local anesthesia. It entails circumferential viscodilation and tensioning of Schlemm’s canal to restore natural aqueous outflow. Canaloplasty is performed with the iTrack™ 250 Canaloplasty Microcatheter System (Ellex Medical Lasers, Adelaide, Australia), a patented microcatheter with an inner lumen that is used to inject high viscosity sodium hyaluronate for safe and effective 360-degree dilation of Schlemm’s canal, the trabecular meshwork, and the outflow collector channels, enabling aqueous humor to exit as normal. Canaloplasty often includes a tensioning device such as a suture/stent to assist in longer term canal patency. By addressing all aspects of the “traditional” or trabeculocanalicular outflow pathway including distal outflow system, canaloplasty helps to significantly lower the IOP. Fig. 32.2 Fornix-based conjunctival peritomy down to bare sclera following application of light cautery. Canaloplasty is accomplished by exposing Schlemm’s canal via nonpenetrating dissection and using the iTrack 250 microcatheter (Fig. 32.1) to circumferentially viscodilate and intubate Schlemm’s canal with a tensioning suture. The microcatheter system is engineered specifically for safe and effective 360-degree viscodilation of Schlemm’s canal. It has a 250-µm atraumatic bulbous tip that helps to bypass collector channel ostia as well as to minimize tissue trauma; the diameter of the working length is 200 µm. The iTrack also contains a fiber optic that enables illumination of the tip so that its passage through the canal can be monitored continuously, and it includes a support wire to enhance “push-ability” during catheterization. Additionally, the working length of the iTrack has the same lubricious coating as cardiac catheters, which facilitates circumferential passage throughout Schlemm’s canal. Typically, anesthesia and akinesia are achieved with a retrobulbar block. A corneal traction suture is placed superiorly next to the limbus. Next, a fornix-based conjunctival incision is created followed by careful dissection of the conjunctiva and Tenon’s capsule down to bare sclera (Fig. 32.2). We prefer a superonasal approach during this step, as it leaves the superior and superotemporal conjunctiva undisturbed in case future incisional surgeries are necessary. Hemostasis is achieved with wet-field cautery. Antifibrotics, such as mitomycin C, are unnecessary. Once the bare sclera is exposed, a superficial one-third to one-half thickness scleral flap is created at the limbus. A 3.5 mm × 3.5 mm parabolic shape may be used; however, individual surgeon preference dictates the shape of the scleral flap. Within the base of the superficial scleral flap a 3 mm × 3 mm deep scleral flap is created with a dissection plane just superficial to the choroid. The choroid may be slightly visible beneath the deep scleral flap. The deep scleral flap is dissected anteriorly to unroof Schlemm’s canal (Fig. 32.3). While dissecting forward, the surgeon pays close attention to identifying the cross-striations of the scleral spur. This verifies that the surgeon has reached the correct depth and plane while fashioning the deep flap. Identifying the cross-striations of the scleral spur also anatomically orients the surgeon to the location of Schlemm’s canal, which is immediately anterior. At this point, a paracentesis is performed to lower the IOP to the middle to high single digits. This serves to decompress the eye and decrease the risk of perforating into the anterior chamber while isolating Schlemm’s canal and creating Descemet’s window. Once the canal is identified, the deep flap is carefully dissected further anteriorly to detach Schwalbe’s line and to create an appropriately sized Descemet’s window, which should at minimum be 500 µm (Fig. 32.4). Aqueous humor usually, but not always, percolates through the Descemet’s window. The iTrack microcatheter is then inserted through one of the canal ostia. The lights on the microscope are dimmed to enable visualization of the lighted tip of the microcatheter as it is advanced through Schlemm’s canal (Fig. 32.5). If an obstruction is encountered during cannulation, the microcatheter may be retracted, inserted into the opposite ostia, and cannulated in the other direction to achieve successful passage. Once circumferential cannulation is completed, a 10-0 or 9-0 polypropylene (Prolene, Ethicon, Switzerland) suture is tied to the distal end of the catheter, which is retracted, introducing the suture into Schlemm’s canal. As the suture is pulled through, ophthalmic viscosurgical device (OVD) is injected at a rate of 0.5 µL for each arc segment of two clock positions, that is, a 1/8th turn of the OVD injector for every two clock positions. The suture is tied, placing appropriate tension on the canal without inadvertently performing a trabeculotomy. Suture tensioning is important, as it enables tension to be transmitted 360 degrees on Schlemm’s canal and keeping its long-term patency.
32 Canaloplasty
Case Presentation
The Procedure
Rationale Behind the Procedure
Surgical Technique
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