Viscocanalostomy and canaloplasty, forms of nonpenetrating glaucoma surgery, have been proposed as alternatives to trabeculectomy, the traditional surgical treatment of primary open-angle glaucoma (POAG). This document addresses viscocanalostomy and canaloplasty.

Note: Please see the following related document for additional information:

• SURG.00087 Transciliary Fistulization for the Treatment of Glaucoma

Investigational and Not Medically Necessary:

Viscocanalostomy is considered investigational and not medically necessary for all indications, including but not limited to the treatment of primary open-angle glaucoma (POAG).

Canaloplasty is considered investigational and not medically necessary for all indications, including but not limited to the treatment of primary open-angle glaucoma (POAG).

Surgical intervention is indicated in the management of glaucoma when medication therapies have failed to adequately reduce intraocular pressure (IOP). The established surgical procedure to which alternatives have been compared is trabeculectomy. This procedure creates a conjunctival reservoir or "filtering bleb" which reduces IOP by allowing aqueous humor to enter the subconjunctival space. Alternative surgical methods under evaluation include viscocanalostomy and canaloplasty. Viscocanalostomy unroofs and dilates a portion of Schlemm's canal, and a high viscosity (viscoelastic) solution is used to open the canal and create a passage from Schlemm's canal to a scleral reservoir. A related procedure, canaloplasty, requires the dilation of the entire length of Schlemm's canal with a suture loop between the canal and the trabecular meshwork using a specialized microcatheter (iTrack^™) device. 

Viscocanalostomy

Chai and Loon (2010) performed a meta-analysis comparing the safety and efficacy of viscocanalostomy with the gold standard of trabeculectomy. Ten randomized controlled trials comprised of a total of 458 eyes of 397 subjects with medically uncontrolled glaucoma were included in the analysis. The number of eyes in each study ranged from 20 to 60, with follow-up ranging from 6 months to 4 years. The majority of eyes (81%) had POAG, while 16.4% had secondary open angle glaucoma (OAG), and 1.7% had primary angle closure glaucoma. Meta-analysis found that trabeculectomy had a significantly better pressure-lowering outcome. The difference in intraocular pressure (IOP) between the treatments was 2.25 mm Hg at 6 months, 3.64 mm Hg at 12 months, and 3.42 mm Hg at 24 months. Viscocanalostomy had a significantly higher relative risk (RR) of perforation of Descemet membrane (RR = 7.72). In contrast, viscocanalostomy had significantly fewer postoperative events compared with trabeculectomy (hypotony RR = 0.29, hyphema RR = 0.50, shallow anterior chamber RR = 0.19, and cataract formation RR = 0.31). Trabeculectomy had a greater pressure lowering effect. Although viscocanalostomy had a better risk profile, most of the adverse events associated with trabeculectomy were considered to be mild and reversible.

A study by Gilmour and colleagues (2009), included in the previously noted meta-analysis, consisted of 50 eyes of 43 individuals with open angle glaucoma randomized to have either a viscocanalostomy (25 eyes) or trabeculectomy (25 eyes) and prospectively followed at regular intervals for up to 60 months. A successful outcome was defined as IOP less than 18 mm Hg with no medications; a qualified success was defined as IOP less than 18 mm Hg with or without topical treatment. One person from each group was lost to follow-up. At baseline, subjects had a mean IOP of 25 mm Hg and were using an average of 1.4 medications. At mean follow-up of 40 months (range, 6 to 60 months), 10 subjects (42%) in the trabeculectomy group had achieved success compared to 5 (21%) in the viscocanalostomy group. Although 19 individuals (79%) in both groups achieved qualified success, fewer from the trabeculectomy group required additional topical treatment (50% vs. 83%) to achieve qualified success. There were more early postoperative complications in the trabeculectomy group (e.g., hypotony, wound leak, choroidal detachment), but these had no long-term effect on IOP control or cataract formation. The authors concluded that trabeculectomy was more effective than viscocanalostomy at lowering IOP and maintaining long term control of IOP in those with POAG.

Canaloplasty 

Lewis and colleagues (2007) reported on a nonrandomized, uncontrolled study of 94 individuals who underwent a canaloplasty for POAG with an IOP of at least 16 mm Hg or higher. Seventy-four individuals had successful tension suture placement with a resulting mean IOP of 15.3 +/– 3.8 mm Hg at one year postop compared to a mean IOP of 24.7 +/- 4.8 mm Hg at baseline. There was a high loss to follow-up; at one year, only 48 of the 74 individuals had follow-up. There were many uncontrolled variables such as suture placement versus nonsuture placement, and cataract surgery with canaloplasty versus canaloplasty only, which could influence the results. It is unclear how the uncontrolled variables and those lost to follow up affected the reported results. In addition to the uncontrolled variables, this study was limited by lack of randomization.

In an international multicenter prospective study, Shingleton and colleagues (2008) evaluated the safety and efficacy of canaloplasty to treat open-angle glaucoma combined with clear corneal phacoemulsification and posterior chamber intraocular lens implantation. Data from 54 eyes that had combined glaucoma and cataract surgery performed by 11 surgeons at 9 study sites were examined. The Schlemm canal and anterior segment angle morphology were assessed by intraoperative and postoperative high resolution ultrasound imaging. Upon comparison of baseline with postoperative data it was found that postoperatively the mean baseline IOP had decreased at 1 month, 3 months, 6 months, and 12 months. Medication usage had also decreased at 12 months postoperatively. Surgical complications occurred in five eyes and included hyphema, Descemet tear, and iris prolapse. Limitations of this study include lack of randomization and lack of a control group present. The authors noted that "additional studies to evaluate this new technique in relation to existing treatments as well as other types of glaucoma are recommended."

In an ongoing international multicenter prospective open-label study, Lewis and colleagues (2009) evaluated the two year post surgical safety and efficacy of canaloplasty performed for the treatment of OAG. The study group consisted of 127 individuals (127 eyes) of which 97 eyes (76%) had canaloplasty alone and 30 eyes (24%) with significant cataracts had a combined glaucoma-cataract surgery (phacocanaloplasty). Primary outcome measures included IOP and glaucoma medication use. The authors reported at 24 months, all 127 eyes had a mean IOP of 16.0 mm Hg +/- 4.2 (SD) and mean glaucoma medication use of 0.5 +/- 0.8 (baseline values 23.6 +/- 4.8 mm Hg and 1.9 +/- 0.8 medications). Eyes with canaloplasty alone had a mean IOP of 16.3 +/- 3.7 mm Hg and 0.6 +/- 0.8 medications (baseline values 23.2 +/- 4.0 mm Hg and 2.0 +/- 0.8 medications). Eyes with a combined glaucoma-cataract surgery had a mean IOP of 13.4 +/- 4.0 mm Hg and 0.2 +/- 0.4 medications (baseline values 23.1 +/- 5.5 mm Hg and 1.7 +/- 1.0 medication). Also at 24 months, three eyes (3%) had lost visual acuity. Of these eyes, one had posterior capsule opacification, one had a dense cataract, and the reason for the visual acuity decrease in the remaining eye was not specified. A total of 20 (15.7%) of 127 individuals did not meet study analysis criteria due to missed visits. There were 13 post surgical complications reported in 10 eyes and also three complications noted during surgery. Complications reported included suture extrusion, hyphema, and IOP elevation. Limitations of this study included lack of randomization. There was flexibility in individual selection and treatment according to each investigator's current practice. The authors noted "the study design includes additional follow-up and reporting with more extensive subgroup analysis anticipated during the continuing study."

Mosaed and colleagues (2009) performed a literature review comparing traditional (trabeculectomy) and novel glaucoma surgical techniques which included canaloplasty. The authors concluded that trabeculectomy remains the most effective IOP lowering procedure to date; however, it has the highest risk of severe complications. In addition, the authors indicated that canaloplasty may not be able to regularly achieve the lower IOP required in advanced glaucoma.

Grieshaber and colleagues (2010) reported on a prospective single center study evaluating canaloplasty in 60 randomly selected eyes of 60 consecutive African individuals with POAG. The mean preoperative IOP was 45.0 ±12.1 mm Hg. The mean follow-up time was 30.6 ± 8.4 months. The mean IOP at 12 months was 15.4 ± 5.2 mm Hg (n=54), at 24 months 16.3 ± 4.2 mm Hg (n = 51) and at 36 months 13.3 ± 1.7 mm Hg (n=49). For IOP ≤ 21 mm Hg. the complete success rate (without medications) was 77.5% and qualified success rate (with or without medications) was 81.6% at 36 months.

Grieshaber and colleagues (2011) reported on an additional prospective single center study which aimed to assess the safety and efficacy of canaloplasty. This procedure was performed in 32 eyes of 32 consecutive individuals with medically uncontrolled OAG and a follow-up time of over one year. The mean preoperative IOP dropped from 27.3+/-5.6 mm Hg to 12.8+/-1.5 mm Hg at 12 months and was 13.1+/-1.2 mm Hg at 18 months (P<0.001). The complete success rate of an IOP </=21, 18, and 16 mm Hg was 93.8% [95% confidence interval (CI) 0.86-1.0], 84.4% (95% CI 0.73-0.98), and 74.9% (95% CI 0.61-0.92), respectively, at 12 months. The authors concluded that canaloplasty was an efficient method in lowering IOP in OAG in this series, but the procedure had its own distinct risk profile and comparative, randomized long-term studies are awaited to draw final conclusions.

Lewis and colleagues (2011) followed up on their 2007 and 2009 non randomized multicentre studies and reported three year results addressing the safety and efficacy of canaloplasty. The study cohort consisted of adults with OAG having had canaloplasty or combined cataract-canaloplasty surgery. Three years after surgery, all eyes studied (n = 157) had a mean IOP of 15.2 mm Hg ± 3.5 (SD) and mean glaucoma medication use of 0.8 ± 0.9 compared with a baseline IOP of 23.8 ± 5.0 mm Hg on 1.8 ± 0.9 medications. Eyes having undergone combined cataract-canaloplasty surgery had a mean IOP of 13.6 ± 3.6 mm Hg while on 0.3 ± 0.5 medications compared with a baseline IOP of 23.5 ± 5.2 mm Hg on 1.5 ± 1.0 medications. IOP and medication use results in all eyes were decreased from baseline at every time point (P<.001). Late postoperative complications included cataract (12.7%), transient IOP elevation (6.4%), and partial suture extrusion through the trabecular meshwork (0.6%).

In their Preferred Practice Pattern for POAG, the American Academy of Ophthalmology (AAO) (2010) states: "Nonpenetrating glaucoma surgery is an alternative to trabeculectomy." However, they further note: "The precise role of non penetrating surgery in the management of glaucoma remains to be determined." The AAO also indicates that canaloplasty with a tensioning suture is currently under evaluation. A report issued by the AAO in 2011 assessed novel glaucoma procedures including canaloplasty. The advantages of canaloplasty were stated to include: "the circumferential treatment of Schlemm's canal, the use of fiberoptics to confirm placement, the use of ultrasound biomicroscopy to confirm suture tension, and the ability to convert to trabeculectomy intraoperatively if needed." Possible disadvantages reported were: "external dissection, which is more difficult and time-consuming than other angle-based procedures, and the conjunctival scarring that may increase the risk of failure of a subsequent trabeculectomy." The authors noted that randomized trials are needed.

The National Institute for Health and Clinical Excellence (NICE) (2008) issued guidance on canaloplasty and stated: "Current evidence on the safety and efficacy of canaloplasty for primary open-angle glaucoma is inadequate in both quality and quantity. Therefore, this procedure should only be used in the context of research or formal prospective data collection." Theoretical safety concerns raised by NICE included anterior chamber perforation, tearing of Descemet's membrane resulting in corneal opacification or retinal damage, intraocular inflammation caused by suture, cataract formation, sustained increases in IOP, hypotony, and bleb formation or suture exposure with endophpthalmitis.

Although initial study results may show potential promise, there is a need for results from well designed randomized controlled comparative trials to clearly determine the safety and efficacy of viscocanalostomy and canaloplasty.

According to the AAO (2010), glaucoma is the second leading cause of blindness worldwide, with a total of approximately 8.4 million people blind as a result of glaucoma. In the United States, it is estimated that 2% of people over 40 have POAG. Glaucoma is a group of diseases, which can damage the eye's optic nerve and result in vision loss and blindness. POAG, the most common type of glaucoma, is associated with a build up of aqueous fluid pressure within the eye, which can lead to visual field loss and optic nerve damage usually without any associated pain or discomfort. There is no visible abnormality in the anterior chamber angle; however, the aqueous fluid is unable to flow correctly.

In the management of POAG, the goal is to reduce the IOP to slow the development of optic nerve damage. The IOP can be reduced by medical treatment or surgery (alone or in combination). Surgical procedures may be indicated in individuals with glaucoma when the target IOP cannot be reached pharmacologically. Laser trabeculoplasty is a procedure that leads to tissue remodeling and improved aqueous humor outflow to reduce IOP. The traditional surgery is a trabeculectomy, a filtering surgery in which a surgical excision of a small portion of the trabecular tissue, sclera and, in some cases cornea, is made in order to facilitate drainage of aqueous humor.

Viscocanalostomy and canaloplasty have been proposed as nonpenetrating surgical alternatives to trabeculectomy. The viscocanalostomy procedure involves deroofing the Schlemm's canal and injecting viscoelastic sodium hyaluronate into the canal. The canaloplasty has been described as an extension of viscocanalostomy with the addition of a flexible microcatheter to dilate the full circumference of Schlemm's canal, the placement of a permanent suture under tension in the canal, and the creation of an intrascleral reservoir. A significant difference between viscocanalostomy and canaloplasty is that canaloplasty attempts to open the entire length of the Schlemm's canal rather than one section of it.

The iTrack^™ (iScience Interventional Corp., Menlo Park, CA) received 510(k) marketing clearance from the FDA in 2004 as a surgical ophthalmic microcannula indicated for the general purpose of "fluid infusion and aspiration, as well as illumination, during surgery." In 2008, the iTrack canaloplasty microcatheter received FDA-clearance for the indication of "catheterization and viscodilation of Schlemm's canal to reduce intraocular pressure in adult patients with open angle glaucoma."

Hyphema: Bleeding in the eye.

Schlemm's canal: A circular canal in the eye that drains aqueous humor from the anterior chamber of the eye into the anterior ciliary veins.

Trabecular tissue: A mesh-like structure inside the eye at the iris-scleral junction of the anterior chamber angle; filters aqueous fluid and controls its flow into the canal of Schlemm, prior to its leaving the anterior chamber.

The following codes for treatments and procedures applicable to this document are included below for informational purposes.  Inclusion or exclusion of a procedure, diagnosis or device code(s) does not constitute or imply member coverage or provider reimbursement policy.  Please refer to the member's contract benefits in effect at the time of service to determine coverage or non-coverage of these services as it applies to an individual member.

When services are Investigational and Not Medically Necessary:
For the procedure codes listed below for all diagnoses; or when the code describes a procedure indicated in the Position Statement section as investigational and not medically necessary.

Future ICD-10 coding (effective 10/01/2013)
A draft of ICD-10 Coding related to this document, as it might look today, is available for reference and comments at: Appendix 1: Future ICD-10 coding

Peer Reviewed Publications:

1. Chai C, Loon SC. Meta-analysis of viscocanalostomy versus trabeculectomy in uncontrolled glaucoma. J Glaucoma. 2010; 19(8):519-527.
2. Gilmour DF, Manners TD, Devonport H, et al. Viscocanalostomy versus trabeculectomy for primary open angle glaucoma: 4-year prospective randomized clinical trial. Eye (Lond). 2009; 23(9):1802-1807.
3. Godfrey DG, Fellman RL, Neelakantan A. Canal surgery in adult glaucomas. Curr Opin Ophthalmol. 2009; 20(2):116-121.
4. Grieshaber MC, Fraenkl S, Schoetzau A, et al. Circumferential Viscocanalostomy and Suture Canal Distension (Canaloplasty) for Whites With Open-angle Glaucoma. J Glaucoma. 2011; 20(5):298-302.
5. Grieshaber MC, Pienaar A, Olivier J, Stegmann R. Canaloplasty for primary open-angle glaucoma: long-term outcome. Br J Ophthalmol. 2010; 94(11):1478-1482.
6. Lewis RA, von Wolff K, Tetz M, et al. Canaloplasty: circumferential viscodilation and tensioning of Schlemm's canal using a flexible microcatheter for the treatment of open-angle glaucoma in adults: interim clinical study analysis. J Cataract Refract Surg. 2007; 33(7):1217-1226.
7. Lewis RA, von Wolff K, Tetz M, et al. Canaloplasty: circumferential viscodilation and tensioning of Schlemm canal using a flexible microcatheter for the treatment of open-angle glaucoma in adults: two-year interim clinical study results. J Cataract Refract Surg. 2009; 35(5):814-824.
8. 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):682-90.
9. Mosaed S, Dustin L, Minckler DS. Comparative outcomes between newer and older surgeries for glaucoma. Trans Am Ophthalmol Soc. 2009; 107:127-133.
10. Shingleton B, Tetz M, Korber N. Circumferential viscodilation and tensioning of Schlemm canal (canaloplasty) with temporal clear corneal phacoemulsification cataract surgery for open-angle glaucoma and visually significant cataract: one-year results. J Cataract Refract Surg. 2008; 34(3):433-440.

Government Agency, Medical Society, and Other Authoritative Publications:

1. American Academy of Ophthalmology (AAO). Primary Open angle glaucoma. Preferred Practice Pattern. Revised October 2010. For additional information visit the AAO website: http://one.aao.org/CE/PracticeGuidelines/PPP.aspx?sid=ca9ec1b5-2567-4e85-96f6-b6540e5ac5a1. Accessed on September 27, 2011.
2. Francis BA, Singh K, Lin SC, et al. Novel glaucoma procedures: a report by the American Academy of Ophthalmology. Ophthalmology. 2011; 118(7):1466-1480.
3. National Institute for Health and Clinical Excellence (NICE). Canaloplasty for open-angle glaucoma. Interventional Procedure Guidance 260. London, UK: NICE; May 2008. Available at: http://www.nice.org.uk/nicemedia/pdf/IPG260Guidance.pdf. Accessed on September 27, 2011.
4. U.S. Food and Drug Administration 510(k) Premarket Notification Database. Summary of Safety and Effectiveness. iScience Interventional Ophthalmic Microcatheter. No. K080067. Rockville, MD: FDA. July 18, 2008. Available at: http://www.accessdata.fda.gov/cdrh_docs/pdf8/K080067.pdf. Accessed on September 27, 2011.

1. National Institutes of Health, the National Eye Institute. Facts about Glaucoma. Last reviewed September 2009. Available at: http://www.nei.nih.gov/health/glaucoma/glaucoma_facts.asp. Accessed on October 8, 2011.
2. The Glaucoma Foundation. Available at: http://www.glaucomafoundation.org/. Accessed on October 8, 2011.

Canaloplasty
iTrack^™ Microcatheter
Viscocanalostomy

The use of specific product names is illustrative only.  It is not intended to be a recommendation of one product over another, and is not intended to represent a complete listing of all products available.