Clinical UM Guideline

This document addresses viscocanalostomy which is a form of non-penetrating glaucoma surgery.

Viscocanalostomy is proposed as an alternative to trabeculectomy, the traditional surgical treatment of primary open-angle glaucoma (POAG).

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

• CG-SURG-125 Canaloplasty

Not Medically Necessary:

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

The following codes for treatments and procedures applicable to this guideline 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 Not Medically Necessary:
For the procedure codes listed below when specified as viscocanalostomy or when the code describes a procedure indicated in the Clinical Indications section as not medically necessary.

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. A trabeculectomy 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.

Chai and Loon (2010) performed a meta-analysis comparing the safety and efficacy of viscocanalostomy with the gold standard of trabeculectomy. A total of 10 randomized controlled trials comprised of 458 eyes from 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, 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 to trabeculectomy: hypotony (RR=0.29), hyphema (RR=0.50), shallow anterior chamber (RR=0.19), and cataract formation (RR=0.31). 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.

A Cochrane review (Edaly, 2014) compared the effectiveness of non-penetrating trabecular surgery with conventional trabeculectomy in persons with glaucoma and reached similar conclusions. Five studies (Cillino, 2005; El Sayyad, 2000; Kobayashi, 2003; Russo, 2008; Yalvac, 2004) were included in the review for a total of 311 eyes (247 participants). A total of 160 eyes in the trabeculectomy group were compared to 151 eyes that had non-penetrating glaucoma surgery. The odds of success in viscocanalostomy participants was lower than in trabeculectomy participants (odds ratio [OR], 0.33; 95% confidence interval [CI], 0.13 to 0.81). The authors reported that some limited evidence was provided that control of IOP is better with trabeculectomy than viscocanalostomy.

In a retrospective multicenter study, Grieshaber and colleagues (2015) assessed the safety and efficacy of viscocanalostomy performed for OAG in subjects in Europe and South Africa. A total of 726 eyes of 726 subjects with primary OAG (POAG) and pseudoexfoliative glaucoma (PXFG) were included. The mean IOP before surgery was 42.6 ± 14.2 mm Hg for all cases, 29.6 ± 6.6 mm Hg for Europeans and 48.1 ± 12.9 mm Hg for South Africans. The follow-up time was 86.2 ± 43.1 months. Mean IOP was 15.4 ± 3.6 mm Hg at 5 years, 15.5 ± 4.4 mm Hg at 10 years and 16.8 ± 4.2 mm Hg at 15 years. The qualified success rate for an IOP of 21, 18 or 16 mm Hg or less after 5 years was 92% (95% CI, 0.88-0.96), 70% (95% CI, 0.63-0.77) and 43% (95% CI, 0.36-0.51) in Europeans, and 90% (95% CI, 0.87-0.93), 77% (95% CI, 0.74-0.81) and 67% (95% CI, 0.63-0.72) in South Africans, respectively. No difference was reported in the POAG and PXFG success rates with an IOP of 21, 18 or 16 mm Hg or below at 5 years (p=0.64, p=0.20, p=0.22, respectively). Postoperatively, laser goniopuncture was performed on 127 eyes (17.7%), lowering the pressure from 23.1 ± 1.9 mm Hg to 15.0 ± 2.2 mm Hg. No significant complications were noted. The authors concluded that viscocanalostomy is “a procedure to consider in patients in whom trabeculectomy is not advisable.” This study contained numerous limitations including a potential for “patient selection bias due to data availability and follow-up losses.”

The American Academy of Ophthalmology (AAO) Preferred Practice Pattern for POAG (2020) states:

The goals of managing patients with POAG are as follows:

• Control of IOP in the target range
• Stable optic nerve/RNFL status
• Stable visual fields

The effects of treatment, as well as, the patient’s quality of life, comorbidities, and life expectancy are to be considered in the decision-making process about therapy.

The rationale for nonpenetrating glaucoma surgery is that by avoiding a continuous passageway from the anterior chamber to the subconjunctival space, the incidence of complications such as bleb-related problems and hypotony can be reduced. The nonpenetrating procedures have a higher degree of surgical difficulty compared with trabeculectomy and they require special instrumentation.

Viscocanalostomy: Viscocanalostomy includes deep sclerectomy along with expansion of Schlemm’s canal using an ophthalmic viscoelastic device. The procedure is intended to allow passage of aqueous humor through the trabeculodescemetic membrane window and into the physiologic outflow pathway through Schlemm’s canal. Randomized clinical trials comparing viscocanalostomy with trabeculectomy suggest greater IOP reduction with trabeculectomy but fewer complications with viscocanalostomy. A 2014 Cochrane Systematic Review found some limited evidence that control of IOP was better with trabeculectomy than with viscocanaloplasty, but conclusions could not be drawn for deep sclerectomy, and quality of life outcomes may be needed to differentiate among procedures. Thus, the selection of viscocanalostomy and deep sclerectomy over trabeculectomy should be left to the discretion of the treating ophthalmologist, in consultation with the individual patient. (I-, Insufficient Quality, Strong Recommendation)

Canaloplasty: In canaloplasty, circumferential viscodilation of Schlemm’s canal using a flexible microcatheter is performed in combination with deep sclerectomy. Dilating the entire canal aims to give aqueous humor access to a greater number of collector channels. A 10-0 polypropylene (Prolene) suture is placed with appropriate tension within Schlemm’s canal when possible to apply inward directed tension on the trabecular meshwork. The safety and efficacy of canaloplasty alone and combined with phacoemulsification was described in a nonrandomized, multicenter clinical trial through 3 years of follow-up. A retrospective case series found lower postoperative IOP with trabeculectomy compared with canaloplasty. In a randomized clinical trial comparing trabeculectomy and canaloplasty, patients in the trabeculectomy group achieved higher success rates and required fewer medications than those in the canaloplasty group, but they also experienced a higher rate of late hypotony.

The severity of glaucoma damage can be estimated according to the following categories:

• Mild: Definite optic disc, RNFL, or macular imaging abnormalities consistent with glaucoma as detailed above and a normal visual field as tested with standard automated perimetry (SAP)
• Moderate: Definite optic disc, RNFL, or macular imaging abnormalities consistent with glaucoma as detailed above, and visual field abnormalities in one hemifield that are not within 5 degrees of fixation
• Severe: Definite optic disc, RNFL, or macular imaging abnormalities consistent with glaucoma as detailed above, and visual field abnormalities in both hemifields and/or loss within 5 degrees of fixation in at least one hemifield as tested with SAP
• Indeterminate: Definite optic disc, RNFL, or macular imaging abnormalities consistent with glaucoma as detailed above, inability of patient to perform visual field testing, unreliable/uninterpretable visual field test results, or visual fields not yet performed

In summary, evidence indicated that trabeculectomy is more effective at lowering intraocular pressure (IOP) compared to viscocanalostomy, which is not widely recommended.

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.

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. Cillino S, Di Pace F, Casuccio A, Lodato G. Deep sclerectomy versus punch trabeculectomy: effect of low-dosage mitomycin C. Ophthalmologica. 2005; 219(5):281-286.
3. El Sayyad F, Helal M, El-Kholify H, et al. Nonpenetrating deep sclerectomy versus trabeculectomy in bilateral primary open-angle glaucoma. Ophthalmology. 2000; 107(9):1671-1674.
4. 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.
5. Godfrey DG, Fellman RL, Neelakantan A. Canal surgery in adult glaucomas. Curr Opin Ophthalmol. 2009; 20(2):116-121.
6. Kobayashi H, Kobayashi K, Okinami S. A comparison of the intraocular pressure-lowering effect and safety of viscocanalostomy and trabeculectomy with mitomycin C in bilateral open-angle glaucoma. Graefes Arch Clin Exp Ophthalmol. 2003; 241(5):359-366.
7. Russo V, Scott IU, Stella A, et al. Nonpenetrating deep sclerectomy with reticulated hyaluronic acid implant versus punch trabeculectomy: a prospective clinical trial. Eur J Ophthalmol. 2008; 18(5):751-757.
8. Wagdy FM. Canaloplasty versus viscocanalostomy in primary open angle glaucoma. Electron Physician. 2017 Jan 25; 9(1):3665-3671.
9. Yalvac IS, Sahin M, Eksioglu U, et al. Primary viscocanalostomy versus trabeculectomy for primary open-angle glaucoma: three-year prospective randomized clinical trial. J Cataract Refract Surg. 2004; 30(10):2050-2057.

Government Agency, Medical Society, and Other Authoritative Publications:

1. American Academy of Ophthalmology (AAO). Primary Open angle glaucoma. Preferred Practice Pattern. Revised September 12, 2020. For additional information visit the AAO website: http://one.aao.org. Accessed on April 8, 2024.
2. Eldaly MA, Bunce C, Elsheikha OZ, Wormald R. Non-penetrating filtration surgery versus trabeculectomy for open-angle glaucoma. Cochrane Database Syst Rev. 2014;(2):CD007059.
3. 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.
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 October 18, 2024.

1. National Institutes of Health, the National Eye Institute. Facts about Glaucoma. Available at: https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/glaucoma. Accessed on October 18, 2024.

iTrack^™ Microcatheter
Viscocanalostomy

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