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Canaloplasty
Summary
Canaloplasty provides a surgical means of safely lowering intraocular pressure in patients with open angles without depending on the function of a bleb or external drainage device. Working in the canal space provides a means of achieving moderate IOP control while avoiding many of the complications of traditional filtration surgery.
Introduction
The concept of lowering intraocular pressure by enhancing outflow by modifying the canal of Schlemm and collectors has long been a goal in the surgical management of glaucoma. Trabeculectomy was first conceived as a surgical approach to increase flow through the trabecular meshwork and canal. Only later was it realized that pressure was reduced as aqueous was redirected through the excised scleral fistula and into the subconjunctival space with the creation of a bleb. Canal-based nonpenetrating surgery, glaucoma surgery not dependent on a fistula or bleb, remained an elusive goal. The introduction of microinstruments and viscoelastic provided the opportunity for Stegmann et al. to publish a procedure called viscocanalostomy demonstrating that IOP could be successfully lowered in patients with open angle glaucoma. Viscocanalostomy involves up to 4 clock hours of the canal and achieves moderate IOP lowering. Efforts to utilize more of the canal and provide greater IOP reduction required the development of a flexible microcatheter that could be thread the full length of the canal. Thus evolved the procedure, canaloplasty. It uses a similar surgical access site to the canal as viscocanalostomy, but dilates then stents the full 360 degrees of canal to achieve longer-lasting and greater IOP lowering.
Indications and Contraindications
Indications
In general, the value of canaloplasty has to do with the higher degree of short- and long-term safety as compared to incisional glaucoma procedures. The indications for canaloplasty are limited to open angle glaucoma. An open angle is necessary for adequate flow through the trabecular meshwork, into the enhanced canal and collector system. There may be circumstances where a narrow or closed angle is reversed especially when the surgery is combined with cataract removal. However, this is the exception. As compared to other glaucoma procedures, specifically a trabeculectomy or drainage device, canaloplasty is safer. Hypotony is avoided. Bleb and bleb-related complications such as dellen and blebitis are very uncommon. Contact lens wearers may resume their lenses. Patients on blood thinners have very little risk of a choroidal hemorrhage. Thus, patients considered at risk with interventional glaucoma surgery may safely undergo canaloplasty.
Open Angle Glaucoma.
For optimal outcomes, canaloplasty requires open angles. Thus, the open angle glaucomas are the most common indication for canaloplasty. This includes pigmentary dispersion glaucoma, pseudoexfoliation syndrome, steroid-induced glaucoma and juvenile-onset glaucoma. Canaloplasty is not effective in some of the secondary glaucoma such as traumatic angle recession and neovascular. Performing canaloplasty in inflammatory (or uveitic) glaucoma is controversial and has not been studied.
High Myopia.
The use of mitomycin with trabeculectomy in patients with glaucoma, especially those with high myopia, has been associated with the condition, hypotony maculoplasty. Canaloplasty is an effective alternative with high myopes as it successfully lowers IOP without causing hypotony.
Ocular Surface Disease.
Creation of a bleb requires healthy conjunctiva. Eyes with ocular surface disease may present more challenges during surgery due to thinning and engorged vessels. Postoperatively chronic inflammation predisposes to bleb scarring. Various ocular surface conditions are associated with a higher risk of bleb failure including chronic topical drug allergies, recurrent conjunctival inflammation, infections (such as blepharitis and conjunctivitis), and prior conjunctival surgery. Canaloplasty, since it is not dependent on a bleb or the health of the conjunctiva for function, is a good alternative.
Immunocompromised Patients.
The presence of a bleb is a potential site for infection or wound leak. The ubiquitous use of antifibrotic agents such as mitomycin or 5-fluorouracil in trabeculectomy surgery induces thinner, more avascular blebs that present even greater risk for infection and conjunctival thinning. This is particularly true for the immunocompromised patient at early and late stages following trabeculectomy. Since blebs are uncommon after canaloplasty and not necessary for function, the patient who is immunocompromised is at less risk for infection and erosion.
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