Coverage Policy Manual
Policy #: 2011064
Category: Medicine
Initiated: September 2011
Last Review: April 2024
  Viscocanalostomy and Canaloplasty
Description:
Glaucoma surgery is intended to reduce intraocular pressure (IOP) when the target IOP cannot be reached with medications. Due to complications with established surgical approaches such as trabeculectomy, alternative surgical treatments such as transluminal dilation by viscocanalostomy and canaloplasty are being evaluated for patients with glaucoma.
 
Glaucoma is the leading cause of irreversible blindness worldwide and is characterized by elevated intraocular pressure (IOP). In 2020, glaucoma affected approximately 52.7 million individuals globally, with a projected increase to 79.8 million in 2040 (Allison, 2021). Glaucoma has been reported to be 7 times more likely to cause blindness and 15 times more likely to cause visual impairment in Black individuals as compared to White individuals. In the U.S. in 2010, Black individuals had the highest prevalence rate of primary open angle glaucoma at 3.4% compared to 1.7% among White individuals.
 
In the primary (conventional) outflow pathway from the eye, aqueous humor passes through the trabecular meshwork, enters a space lined with endothelial cells (Schlemm’s canal), drains into collector channels, and then into the aqueous veins. Increases in resistance in the trabecular meshwork and/or the inner wall of Schlemm’s canal can disrupt the balance of aqueous humor inflow and outflow, resulting in an increase in IOP and glaucoma risk.
 
Surgical intervention may be indicated in patients with glaucoma when the target IOP cannot be reached pharmacologically. Trabeculectomy (guarded filtration surgery) is the most established surgical procedure for glaucoma, allowing aqueous humor to directly enter the subconjunctival space. This procedure creates a subconjunctival reservoir with a filtering “bleb” on the eye, which can effectively reduce IOP, but is associated with numerous and sometimes sight-threatening complications (e.g., leaks, hypotony, choroidal effusions and hemorrhages, hyphemas or bleb-related endophthalmitis) and long-term failure. Other surgical procedures (not addressed in this policy) include trabecular laser ablation and deep sclerectomy, which removes the outer wall of Schlemm’s canal and excises deep sclera and peripheral cornea.
 
More recently the Trabectome™, an electrocautery device with irrigation and aspiration, has been used to selectively ablate the trabecular meshwork and inner wall of Schlemm’s canal without external access or creation of a subconjunctival bleb. IOP with this ab interno procedure is typically higher than the pressure achieved with standard filtering trabeculectomy. Aqueous shunts may also be placed to facilitate drainage of aqueous humor (see policy number 2010017). Complications of anterior chamber shunts include corneal endothelial failure and erosion of the overlying conjunctiva.
 
Alternative nonpenetrating methods that are being evaluated for glaucoma are viscocanalostomy and canaloplasty. Viscocanalostomy is a variant of deep sclerectomy and unroofs and dilates Schlemm’s canal without penetrating the trabecular meshwork or anterior chamber. A high-viscosity viscoelastic solution, such as sodium hyaluronate, is used to open the canal and create a passage from the canal to a scleral reservoir. It has been proposed that viscocanalostomy may lower IOP while avoiding bleb-related complications.
 
Canaloplasty was developed from viscocanalostomy and involves dilation and tension of Schlemm’s canal with a suture loop between the inner wall of the canal and the trabecular meshwork. This ab externo procedure uses the iTrack™ illuminated microcatheter (iScience Interventional) to access and dilate the length of Schlemm’s canal and to pass the suture loop through the canal. An important difference between viscocanalostomy and canaloplasty is that canaloplasty attempts to open the entire length of Schlemm’s canal, rather than one section of it.
 
Since aqueous humor outflow is pressure-dependent, the pressure in the reservoir and venous system is critical for reaching the target IOP. Therefore, some procedures may not be able to reduce IOP below the pressure of the distal outflow system used, e.g., below 15 mm Hg, and are not indicated for patients for whom very low IOP is desired (e.g., those with advanced glaucoma).
 
Regulatory Status
In 2004, iTrack (iScience Interventional) was cleared for marketing by the U.S. Food and Drug Administration (FDA) through the 510(k) process as a surgical ophthalmic microcannula that is indicated for the general purpose of “fluid infusion and aspiration, as well as illumination, during surgery.” In 2008, the iTrack was cleared by the FDA for “catheterization and viscodilation of [the] Schlemm’s canal to reduce intraocular pressure in adult patients with open angle glaucoma.” FDA product code: MPA.
 
In 2017, the OMNI® Surgical System (Sight Sciences, Inc.) was cleared for marketing by the FDA through the 510(k) process as a manually operated device for the delivery of small amounts of viscoelastic fluid during ophthalmic surgery. It is also indicated to cut trabecular meshwork tissue during trabeculotomy procedures (K173332). In 2020, the OMNI® Plus Surgical System was cleared for the same indications for use as the predicate OMNI system (K201953). In 2021, the OMNI® Surgical System was cleared for marketing by the FDA through the 510(k) process for canaloplasty (microcatheterization and transluminal viscodilation of Schlemm's canal) followed by trabeculotomy (cutting of trabecular meshwork) to reduce intraocular pressure in adult patients with primary open-angle glaucoma (K202678). FDA product code: MRH.
 
Coding
The CPT codes for these procedures were changed in 2011. The current codes are as follows:
 
66174 - Transluminal dilation of aqueous outflow canal; without retention of device or stent
66175 - Transluminal dilation of aqueous outflow canal; with retention of device or stent
Policy/
Coverage:
Effective March 2017
 
Meets Primary Coverage Criteria Or Is Covered For Contracts Without Primary Coverage Criteria
 
Canaloplasty meets primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes as a method to reduce intraocular pressure in patients with open-angle glaucoma under the following conditions:
 
    • Medical therapy has failed to adequately control intraocular pressure, AND
    • The patient is not a candidate for any other intraocular pressure lowering procedure (e.g. trabeculectomy or glaucoma drainage implant) due to a high risk for complications.
 
Does Not Meet Primary Coverage Criteria Or Is Investigational For Contracts Without Primary Coverage Criteria
 
Viscocanalostomy does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For members with contracts without primary coverage criteria, viscocanalostomy is considered investigational.  Investigational services are specific contract exclusions in most member benefit certificates of coverage.
 
Canaloplasty as a method to reduce intraocular pressure in all other conditions, including but not limited to, angle-closure glaucoma does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.  
  
For members with contracts without primary coverage criteria, canaloplasty as a method to reduce intraocular pressure in all other conditions, including but not limited to, angle-closure glaucoma is considered investigational. Investigational services are exclusions in most member benefit certificates of coverage.
 
Effective September 2013- February 2017
 
Meets Primary Coverage Criteria Or Is Covered For Contracts Without Primary Coverage Criteria
 
Canaloplasty meets primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes as a method to reduce intraocular pressure in patients with chronic primary open-angle glaucoma under the following conditions:
 
    • Medical therapy has failed to adequately control intraocular pressure, AND The patient is not a candidate for any other intraocular pressure lowering procedure (e.g. trabeculectomy or glaucoma drainage implant) due to a high risk for complications.
    • Canaloplasty as a method to reduce intraocular pressure in all other conditions, including but not limited to, angle-closure glaucoma does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
  
For members with contracts without primary coverage criteria, canaloplasty as a method to reduce intraocular pressure in all other conditions, including but not limited to, angle-closure glaucoma is considered investigational. Investigational services are exclusions in most member benefit certificates of coverage.
 
Does Not Meet Primary Coverage Criteria Or Is Investigational For Contracts Without Primary Coverage Criteria
 
Viscocanalostomy does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For members with contracts without primary coverage criteria, viscocanalostomy is considered investigational.  Investigational services are specific contract exclusions in most member benefit certificates of coverage.
 
Viscocanalostomy does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For members with contracts without primary coverage criteria, viscocanalostomy is considered investigational.  Investigational services are specific contract exclusions in most member benefit certificates of coverage.
 
Rationale:
This policy was originally developed in September 2011. It is being updated with a search of the MEDLINE database through August 2013. The rationale is being replaced and information is added addressing the use of canaloplasty.
 
Viscocanalostomy
A 2010 meta-analysis by Chai and Loon compared the safety and efficacy of viscocanalostomy with the gold standard of trabeculectomy (Chai, 2010). Ten randomized controlled trials with a total of 458 eyes (397 patients) 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 primary open angle glaucoma, while 16.4% had secondary open angle glaucoma, 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 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’s 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). Although viscocanalostomy had a better risk profile, most of the adverse events associated with trabeculectomy were considered to be mild and reversible.
 
One of the studies included in the systematic review was a randomized trial with 4-year follow-up by Gilmour et al. from 2009 (Gilmour, 2009). Patients (n=43) with open angle glaucoma were randomized to viscocanalostomy (25 eyes) or trabeculectomy (25 eyes) and prospectively followed at regular intervals for up to 60 months. A successful outcome was defined as intraocular pressure (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 patient in each group was lost to follow-up. At baseline, patients 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 patients (42%) in the trabeculectomy group had achieved success compared to 5 patients (21%) in the viscocanalostomy group. Although 19 patients (79%) in both groups achieved qualified success, fewer trabeculectomy patients required additional topical treatment (50% vs. 83%, respectively) to achieve qualified success. There were more early postoperative complications in the trabeculectomy group (e.g., hypotony, wound leak, choroidal detachment), but these did not affect the outcome. At 1 month, conjunctival blebs were observed in 19 (79%) of the trabeculectomy group and 16 (64%) of the viscocanalostomy group. At 12 months, blebs were observed in 19 (79%) of the trabeculectomy group and 14 (56%) of the viscocanalostomy group. The proportion of patients with conjunctival blebs at final follow-up and the statistical significance of these differences were not reported. It was reported that more bleb manipulations (7 vs. 1) and antimetabolites (5 vs. 1) were needed in the trabeculectomy group. The 3 patients who required cataract surgery were all in the viscocanalostomy group.
 
In 2003, Kobayashi et al. reported a within-subject safety and efficacy comparison of trabeculectomy (with mitomycin C) and viscocanalostomy in 25 patients with bilateral primary open-angle glaucoma who had IOP greater than 22 mm Hg under medical therapy (Kobayashi, 2003). Patients were randomly assigned to receive trabeculectomy in one eye and viscocanalostomy (with removal of the internal wall of Schlemm’s canal) in the other eye. Follow-up was performed at 1 and 3 days, 1 and 2 weeks, and 1, 2, 3, 4, 5, 6, 9, and 12 months after surgery. Throughout follow-up, the mean IOP decreased significantly more in trabeculectomy-treated eyes (e.g., from 24.8 to 12.6 mm Hg at 12 months) than in viscocanalostomy-treated eyes (from 25.0 to 17.1 mm Hg). At 12 months, significantly more trabeculectomy-treated eyes achieved an intraocular pressure less than 20 mm Hg without medication (88% vs. 64%, respectively). The mean IOP reduction was 48.9% in trabeculectomy-treated eyes and 30.5% in viscocanalostomy-treated eyes. Overall success, defined as IOP less than 20 mm Hg and IOP reduction greater than 30% with or without glaucoma medication, was not significantly different between the 2 groups (96% for trabeculectomy and 92% for viscocanalostomy). Although trabeculectomy had a greater IOP-lowering effect, there were fewer complications with viscocanalostomy (1 microperforation of Descemet’s membrane compared with 4 cases of shallow anterior chamber and 5 cases of hypotony with IOP <4 mm Hg).
 
Stangos et al. reported the effect of the learning curve on the surgical outcome of viscocanalostomy from a retrospective series of 180 consecutive cases performed by 2 surgeons at a single center in Europe (Stangos, 2012). Overall success, defined as no visual field deterioration with an IOP of 20 mm Hg or less and IOP reduction of 30% or greater compared to baseline values, improved from 64% to 91% when comparing the first 45 to the last 45 cases of the series. Complete success, defined as no medications required, improved from 38% to 73%. Surgical complications were not significantly different between the first and last 45 cases (16 vs. 10, respectively).
 
Canaloplasty
In 2007, Lewis et al. reported interim data analysis from a company-sponsored multicenter (15 centers) safety/efficacy study on canaloplasty using the iTrack microcatheter (Lewis, 2007). Catheterization of the canal was achieved in 83 of 94 patients enrolled (88%); tension sutures were successfully placed in 74 patients (79%) with a mean IOP of 24 mm Hg. At 3-month follow-up, 57 patients (77% of 74 implanted) had an IOP of 16 mm Hg, and at 12 months, 48 patients (65%) had a mean IOP of 15 mm Hg. Ten ocular adverse events (11%) were reported, including hyphema (3%), elevated IOP (3%), Descemet’s membrane detachment, hypotony, choroidal effusion, and exposed closure suture (1% each). Eleven patients (12%) had a subconjunctival bleb, 6 of which resolved by 3 months. The study design included 5-year follow-up. These results were limited by the lack of randomization and high loss to follow-up.
 
Lewis et al. reported 2-year and 3-year results from the multicenter study in 2009 and 2011, respectively (Lewis, 2009; Lewis, 2011). Enrolled in the follow-up study were 157 patients with a diagnosis of primary open-angle glaucoma, pigmentary glaucoma, exfoliative glaucoma, and a baseline IOP of 16 mm Hg or higher before surgery, with a historical IOP of 21 mm Hg or higher. Exclusion criteria were neovascular disease, uveitis, peripheral anterior synechiae, angle recession, and developmental or secondary glaucoma (except for pigmentary and exfoliative glaucoma). At baseline, the mean IOP was 23.8, and patients were on an average 1.8 medications; 21% of eyes were on 3 or more antiglaucoma medications, and 12 eyes (7.6%) were on no medications. Twenty-five eyes (15.9%) were pseudophakic. Canaloplasty (with or without cataract surgery) was successful in 133 eyes (85%). Eyes that did not have placement of a tensioning suture were viscodilated to the extent possible by catheterizing the canal from both ostia. At 3 years postoperatively, 134 study eyes (85% follow-up) had a mean IOP of 15.2 mm Hg and mean glaucoma medication use of 0.8 medications; 4 eyes (3%) were on 3 or more antiglaucoma medications, and 66 eyes (49.3%) were on no medications. Another 7 patients (4.4%) had additional glaucoma surgery. Six eyes lost 2 or more lines of corrected visual acuity related to glaucoma progression. With qualified success defined as achieving IOP of 18 mm Hg or lower (with 0 to 2 medications), success was achieved in 69 of the 89 eyes (77.5%) that had successful suture implantation alone and 24 of the 27 eyes (89%) with successful suture placement combined with phacoemulsification. Early surgical/postoperative complications included microhyphema (12%), hyphema (10%), elevated intraocular pressure (6%), Descemet’s membrane detachment (3%), suture extrusion (1%), and hypotony (1%). Late postoperative complications included cataract (12.7%), transient IOP elevation (6.4%), and partial suture extrusion through the trabecular meshwork (0.6%).
 
Interim 1-year results from a company-sponsored multicenter study were reported in 2008 for 40 patients who had combined canaloplasty and cataract surgery (potential overlap in patients from the study described above) (Shingleton, 2008). Inclusion criteria included: a glaucoma diagnosis of primary open-angle glaucoma (POAG), pigmentary glaucoma, exfoliation glaucoma, or POAG with narrow but not occludable angles after laser iridectomy; a treated IOP of 16 mm Hg or higher at baseline; and a historical untreated IOP of 21 mm Hg or higher. Of the 54 eyes enrolled, successful circumferential catheterization was achieved in 44 eyes (81%), and sutures were successfully placed in 40 eyes (74%). The 14 eyes (26%) that did not have sutures placed were due to the microcatheter entering a collector channel or meeting other resistance during catheterization; successful suture placement was reported to increase with surgeon experience. Two eyes were considered failures, with 1 conversion to trabeculectomy. Clinical results were reported for 25 patients (46% of 54) who were both due for and reported for 12-month follow-up. Of these, 3 eyes (12%) had low subconjunctival blebs at 12 months. No case of suture erosion through the trabecular meshwork or sclera was noted during follow-up. IOP was reduced from a mean of 24 mm Hg to 13 mm Hg at 6 months (reported for 42 eyes; 40 were reported to be successfully treated) and remained under 14 mm Hg in the 25 patients who were evaluated at 12 months. The number of antiglaucoma medications decreased from a mean of 1.5 medications to a mean of 0.1 at 1 month and 0.2 at 12 months. This trial is ongoing, and longer follow-up on a larger number of patients is needed.
 
Koerber et al. reported on 15 of the patients who participated in the multicenter trial described above who had bilateral POAG and received canaloplasty in one eye and viscocanalostomy in the contralateral eye (Koerber, 2012). Qualifying preoperative IOPs were 18 mm Hg or greater with historical IOPs of at least 21 mm Hg. For the canaloplasty eye, the baseline IOP averaged 26.5 mm Hg on 2.1 medications. All patients had successful suture placement. Follow-up at 18 months showed IOP of 14.5 on 0.3 medications. For the viscocanalostomy eye, the baseline eye averaged 24.3 mm Hg on 1.9 medications; follow-up at 18 months showed an average IOP of 16.1 on 0.4 medications. The reduction in IOP from baseline was significantly greater with canaloplasty (12.0 mm Hg) than with viscocanalostomy (8.2 mm Hg). There was no loss in visual acuity and no adverse events from either procedure. The authors noted that this study effectively compares the additional effects of the 2 major additional maneuvers associated with canaloplasty: first, 360 degrees viscodilation of Schlemm’s canal, as opposed to partial dilation achieved with viscocanalostomy, and second, prolonged opening and tensioning of Schlemm’s canal with suture placement.
 
Bull et al. reported an industry-sponsored 3-year prospective, multicenter study of 109 open-angle glaucoma patients (109 eyes) who underwent canaloplasty or combined cataract-canaloplasty surgery (Bull, 2011).  All patients had documented visual field loss and met criteria for the diagnosis of glaucoma and failure of prior medical or laser therapy. A tensioning suture was successfully placed in 98 eyes (89.9%) and 96 eyes (88.1%) completed the 3-year follow-up. Of the 13 patients who did not complete follow-up, 4 (3.7%) had undergone additional glaucoma surgery; these patients were not included in the analysis. In eyes treated with canaloplasty with a successful tensioning suture, IOP decreased from 23 mm Hg on 1.9 medications to 15.1 mm Hg on 0.9 medications. In eyes treated with combined cataract-canaloplasty surgery with a successful tensioning suture, IOP decreased from 24.3 mm Hg on 1.5 medications to 13.8 mm Hg on 0.5 medications. For the 11 eyes that had canaloplasty without suture placement, IOP decreased from 24.4 on 1.9 medications to 15.6 on 1.2 medications. Late postoperative complications included cataracts (19.1%) and transient IOP elevation (1.8%). Patients who received additional glaucoma surgery were excluded from further analysis (instead of being counted as treatment failures), limiting interpretation of these findings.
 
Grieshaber et al. reported a prospective series of 60 consecutive black South African patients with POAG who underwent canaloplasty (Grieshaber, 2010). The mean preoperative IOP was 45 mm Hg. At 12-month follow-up, the IOP was 15 mm Hg (n=54), and at 36 months, the IOP was 13.3 mm Hg (n=49). Eleven patients (18%) were lost to follow-up at 3 years. With qualified success defined as achieving IOP of 21 mm Hg or lower (with or without medications), success was achieved in 40 of 49 patients (82%). When defined as an IOP of 16 mm Hg or less without medications, 47% of eyes met criteria for complete success. There were no severe complications in this series.
 
Mosaed and colleagues published a comparative effectiveness review of newer (Trabectome and canaloplasty) and older (trabeculectomy and Baerveldt shunt) surgeries for glaucoma in 2009 (Mosaed, 2009). Twelve-month outcomes (intracocular pressure adjunctive medications and complications) were compared after glaucoma-only and combined glaucoma-phacoemulsification surgeries. The review found that Trabectome and canaloplasty provided modest IOP reduction (to about 16 mm Hg) with minimal intraoperative or postoperative complications. Results of Baerveldt glaucoma implant IOP reduction were comparable to trabeculectomy (about 12 mm Hg), but typically this shunt required more postoperative IOP-lowering medication (average of 1.3 vs. 0.5 medications, respectively) to achieve a success rate comparable to trabeculectomy. Patients treated with Trabectome required more medications (average of 1.5) to control IOP than patients treated with canaloplasty (average of 0.6). The authors concluded that Trabectome and canaloplasty are reasonable surgical therapy choices for patients in which IOPs in the mid-teens seem adequate; although trabeculectomy remains the most effective IOP-lowering procedure, it also has the highest serious complication rates.
 
Ongoing Clinical Trials
A search of the online site: Clinicaltrials.gov in July 2013 found 2 randomized trials comparing canaloplasty to trabeculectomy. NCT01228799 enrolled 60 patients and was completed December 2012. No publications have been submitted to date. NCT00854256 has an expected enrollment of 60 patients with completion in 2014. NCT01726543 will compare canaloplasty with non-penetrating deep sclerectomy. This study has an estimated enrollment of 80 patients with completion in 2014.
 
Summary
A number of small randomized trials have been conducted that compare viscocanalostomy with trabeculectomy. Meta-analysis of these trials indicates that trabeculectomy has a greater intraocular pressure-lowering effect than viscocanalostomy. Although trabeculectomy is associated with greater postoperative risk, most of the adverse events are mild and reversible. Reduction in intraocular pressure (IOP) has also been shown to be greater with canaloplasty than viscocanalostomy in a small within-subject comparison. The clinical input obtained for viscocanalostomy in 2011 was mixed. Overall, the evidence is insufficient to evaluate health outcomes with this procedure in comparison with currently accepted alternatives.
 
Positive 2- to 3-year outcomes have been reported for canaloplasty, along with a systematic review that found that Trabectome and canaloplasty provided modest IOP reduction (to about 16 mm Hg) with minimal intraoperative or postoperative complications. When combined with expert opinion, the evidence is sufficient  to consider canaloplasty in the subset of patients for whom medical therapy has failed to adequately control intraocular pressure and in whom other surgical procedures (e.g. trabeculectomy or a glaucoma drainage implant) are contraindicated.
 
Practice Guidelines and Position Statements
The 2010 Preferred Practice Patterns on primary open-angle glaucoma from the American Academy of Ophthalmology (AAO) states that glaucoma surgical procedures currently under evaluation are canaloplasty with a tensioning suture (Prolene [Ethicon Inc., Somerville, NJ]), ab interno trabeculotomy using the Trabectome (NeoMedix, Tustin, CA), trabecular meshwork bypass stent, and the Ex-PRESS mini glaucoma shunt (Alcon Laboratories, Inc., Ft. Worth, TX) (AAO, 2010). The AAO considers laser trabeculoplasty as initial therapy in selected patients or as an alternative for patients who cannot or will not use medications reliably due to cost, memory problems, difficulty with instillation, or intolerance to the medication. The AAO considers nonpenetrating glaucoma surgery to be an alternative to trabeculectomy, although the precise role of nonpenetrating surgery in the surgical management of glaucoma remains to be determined. Nonpenetrating glaucoma surgery avoids a continuous passageway from the anterior chamber to the subconjunctival space, reducing the incidence of complications such as bleb-related problems and hypotony. The nonpenetrating procedures have a higher degree of surgical difficulty compared with trabeculectomy and require special instrumentation. The two main types of nonpenetrating glaucoma surgery are viscocanalostomy and nonpenetrating deep sclerectomy.
A 2011 Technology Assessment from the AAO included canaloplasty in its review of novel glaucoma procedures (Francis, 2011). The AAO concluded that all of the techniques and devices reviewed were still in the initial stage (<5 years) of clinical experience and lacking widespread use, with only level III evidence (cohort studies) in support of the procedures. In addition to describing potential advantages and disadvantages of the procedure, it was noted that the long-term effects of a foreign body in Schlemm’s canal are not known.
The 2008 guidance from the United Kingdom’s National Institute for Health and Clinical Excellence (NICE) stated that the current evidence on the safety and efficacy of canaloplasty for primary open-angle glaucoma is inadequate in both quality and quantity and that this procedure should only be used in the context of research or formal prospective data collection (NICE, 2008).
NICE and the National Collaborating Centre for Acute Care published guidance on the diagnosis and management of chronic open angle glaucoma and ocular hypertension in 2009 (NICE, 2009). When comparing penetrating surgery (trabeculectomy) with non-penetrating surgery (deep sclerectomy and viscocanalostomy), the evidence review found moderate quality evidence that trabeculectomy is more effective than non-penetrating surgery in reducing the number of eyes with an unacceptable IOP but was more likely to cause cataract formation and persistent hypotony at 12 to 36 months’ follow-up. There was very low-quality evidence that trabeculectomy is more effective than non-penetrating surgery in reducing IOP from baseline at 6 and 12 months’ follow-up, but the effect size may be too small to be clinically significant. The guidance recommended offering information on the risks and benefits associated with surgery and offering surgery (type not specified) with pharmacological augmentation to people with chronic open angle glaucoma who are at risk of progressing to sight loss despite treatment.
 
2014 Update
A literature search conducted through July 2014 did not reveal any new information that would prompt a change in the coverage statement. The key identified literature is summarized below.
 
The primary literature on canaloplasty consists mainly of case series that compare post-treatment IOP with pretreatment IOP. One retrospective comparative study evaluated outcomes from 33 eyes (33 patients) that underwent canaloplasty and 46 eyes (46 patients) that underwent trabeculectomy during a
2 year period and had a minimum of 12 months’ of follow-up (Ayyala, 2011). This study group was drawn from a larger group of 243 patients who underwent surgery during the same 2 year period (87 canaloplasty procedures and 156 trabeculectomy procedures). The specific procedure was determined by the ability to obtain insurance coverage for canaloplasty, and the groups were comparable in demographics, previous surgery, and visual acuity at baseline. At 12 months after surgery, the mean reduction in IOP from preoperative values was 32% for canaloplasty and 43% for trabeculectomy (p=.072). IOP was slightly lower in the trabeculectomy group (11.6 vs 13.8 mm Hg; p=.03) and fewer patients needed postoperative glaucoma medications. There was no significant difference in surgical reoperation rates between the 2 procedures (15% canaloplasty and 11% trabeculectomy). This study is limited by the potential for bias in the selection of patients for the study. A minority of all surgical patients had 12-month follow-up data and were included in the study; selection into treatment groups was dependent on insurance status.
 
A three year follow-up from an independent series of 214 patients treated with canaloplasty in Europe was reported by Brusini in 2014 (Brusini, 2014).  Mean IOP was reduced from 29.4 mm Hg at baseline to 17.0 mm Hg, after excluding 17 patients (7.9%) who later underwent trabeculectomy,. IOP was 21 mm Hg or lower in 86.2% of patients, 18 mm Hg or lower in 58.6%, and 16 mm Hg or lower in 37.9% of patients. There was a decrease in mean medication use, from 3.3 at baseline to 1.3 at follow-up. Complications, which included hyphema, descement membrane detachment, IOP spikes, and hypotony, were fewer than is typically seen with trabeculectomy. Several disadvantages of the procedure were noted, including the inability to complete the procedure in 16.4% of eyes.
  
2015 Update
A literature search conducted through May 2015 did not reveal any new information that would prompt a change in the coverage statement.  The key identified literature is summarized below.
 
Grieshaber and colleagues reported long-term results of viscocanalostomy in a series of 726 patients. (Grieshaber, 2015). The mean IOP before surgery was 42.6 mm Hg. Mean IOP was 15.4 at 5 years, 15.5 at 10 years, and 16.8 at 15 years. Qualified success (with or without medications) at 10 years of 18 mm Hg or less was 40% in the European population and 59% in the African population. Laser goniopuncture was performed postoperatively on 127 eyes (17.7%). A total of 53 eyes (7.3%) were considered failures and required reoperation. There were no significant complications.
 
In 2015, Matlach and colleagues reported an RCT with 62 patients that compared canaloplasty with trabeculectomy for the treatment of open-angle glaucoma (Matlach, 2015). Patients were included who had medically uncontrolled or not sufficiently lowered IOP and progression of visual field defects or structural changes to the optic disc over time. The primary end point was an IOP of 18 mm or less or an IOP reduction of at least 20% and less than 21 mm Hg without medication. Complete success at 2 years was achieved in 74.2% of patients after trabeculectomy and 39.1% of patients after canaloplasty (p=0.01). The qualified success rate (with medication) did not differ significantly for the 2 groups, although more patients in the canaloplasty group needed IOP-lowering medication (52.2% vs 25.8%). The mean absolute IOP reduction was similar for the 2 interventions. There was a trend (p=0.08) for visual acuity to be lower in the canaloplasty group during follow-up. Trabeculectomy was associated with more frequent postoperative complications, including hypotony (37.5%), choroidal detachment (12.5%) and corneal erosion (43.8%). Scarring of the filtering bleb was a late complication in 25% of trabeculectomy patients. One limitation of this study is the unequal rate of dropouts, with 7 of 30 (23.3%) canaloplasty patients and 1 of 32 (3.1%) trabeculectomy patients lost to follow-up over the 2 years of the study. Another study by this group found higher quality of life (QOL) at 24 months following canaloplasty compared with trabeculectomy in a questionnaire survey of 327 patients.9 Canaloplasty patients had a higher positive postoperative mood, satisfaction with results of surgery, and lower rates of visual and nonvisual symptoms and stress caused by surgery or postsurgical treatment. Difficulties with activities of daily living, such as reading, and complaints like eye burning were significantly lower in the canaloplasty group. Some, but not all, of the questions were from validated QOL questionnaires.
 
2016 Update
A literature search conducted through June 2016 did not reveal any new information that would prompt a change in the coverage statement. The key identified literature is summarized below.
 
In 2015, Voykov and colleagues reported a 5-year follow-up on patients (20 eyes) with open-angle glaucoma who underwent canaloplasty at a single center in Germany (Voykov, 2015). Mean IOP decreased from 25.7 mm Hg at baseline (n=33) to 15.5 mm Hg (n=19) at 1 year, 15.1 mm Hg (n=18) at 3 years, and 14.2 mm Hg (n=18) at 5 years. At each time point, reductions in mean IOP were statistically significant versus baseline (p<0.001). Mean number of medications used was 3.4 at baseline, 1.5 at 1 year, 1.6 at 3 years, and 1.7 at 5 years. At each time point, medication use was significantly lower than baseline (p<0.001). Thirteen (65%) of 20 eyes underwent another surgical procedure due to inadequate IOP control. Median length of time before additional surgery was 24 months (95% CI, 1 to 51 months). The complication rate was low, the most common being hyphema (7/20 [35%] eyes). No sight-threatening complications were reported.
 
Ongoing and Unpublished Clinical Trials
A search of ClinicalTrials.gov in June 2016 did not identify any ongoing or unpublished trials that would likely influence this review.
 
2018 Update
A literature search conducted using the MEDLINE database through February 2018 did not reveal any new information that would prompt a change in the coverage statement.
 
In 2017, the National Institute for Health and Care Excellence (NICE) updated its 2008 guidance on canaloplasty for primary open-angle glaucoma (NICE, 2008; NICE, 2017). The current recommendation is that the “evidence on the safety and efficacy of ab externo canaloplasty for primary open-angle glaucoma is adequate is support the use of this procedure.…”
 
Similarly, in 2017, NICE updated its 2009 guidance on the diagnosis and management of chronic open-angle glaucoma (NICE, 2009; NICE, 2017). When comparing penetrating surgery (trabeculectomy) with nonpenetrating surgery (deep sclerectomy and viscocanalostomy), NICE found moderate-quality evidence that trabeculectomy is more effective than nonpenetrating surgery in reducing the number of eyes with an unacceptable intraocular pressure, but was more likely to cause cataract formation and persistent hypotony at 12- to 36-month follow-up. There was very low quality evidence that trabeculectomy is more effective than nonpenetrating surgery in reducing intraocular pressure from baseline to 6- and 12-month follow-up, but the effect size might have been too small to be clinically significant. The guidance recommended offering information on the risks and benefits associated with surgery and offering surgery (type not specified) with pharmacologic augmentation to people with chronic open-angle glaucoma at risk of progressing to sight loss, despite treatment.
 
2019 Update
Annual policy review completed with a literature search using the MEDLINE database through February 2019. No new literature was identified that would prompt a change in the coverage statement.
 
2020 Update
A literature search was conducted through February 2020.  There was no new information identified that would prompt a change in the coverage statement.   
 
2021 Update
Annual policy review completed with a literature search using the MEDLINE database through February 2021. No new literature was identified that would prompt a change in the coverage statement.
 
2022 Update
Annual policy review completed with a literature search using the MEDLINE database through February 2022. No new literature was identified that would prompt a change in the coverage statement.
 
2023 Update
Annual policy review completed with a literature search using the MEDLINE database through February 2023. No new literature was identified that would prompt a change in the coverage statement. The key identified literature is summarized below.
 
Other case series have evaluated ab interno canaloplasty via the use of the iTrack or OMNI surgical systems in patients with mild-to-moderate primary open-angle glaucoma as a standalone procedure or in combination with cataract surgery (Gallardo, 2022; Koerber, 2022; Murphy, 2022; Ondrejka, 2022; Gallardo, 2022; Gallardo, 2022). Two studies of the OMNI system evaluating a total of 267 eyes with uncontrolled baseline intraocular pressure (IOP) reported mean reductions in IOP and medication use ranging between 5.5 to 6.4 mmHg and 0.6 to 1.1 medications, respectively, over 12-36 months of follow-up (Murphy, 2022; Ondrejka, 2022). Results from the smaller GEMINI study of 120 patients treated with the OMNI system reported an IOP reduction of 8.2 mmHg and a mean decrease of 1.4 medications over 12 months, with 75% of participants achieving a mean IOP ≤18 mmHg; however, analysis was based on mean diurnal ocular pressure following medication washout at baseline, and itis unclear what proportion of patients initially had uncontrolled IOP on medication (Gallardo, 2022). A subgroup analysis of 39 Hispanic participants in the GEMINI study, a demographic disproportionally affected by primary open-angle glaucoma in the U.S., showed comparable results, with a mean IOP decrease of 7.9 and no need for continued medication use in 87% (Gallardo, 2022). One small study utilizing the OMNI system in 27 patients previously treated with the iStent trabecular microbypass stent reported a mean IOP reduction of 5.1 mmHg and a mean decrease of 0.4 medications (Terveen, 2022). Two studies of the iTrack system evaluated a total of 71 eyes treated with canaloplasty alone or in combination with cataract surgery and reported 36 to 48 month outcomes (Gallardo, 2022; Koerber, 2022). Mean IOP reductions ranged from 5.2 to 7.2 mmHg and medication use decreased between 1 to 1.5 medications. Overall, 68.2% to77.2% of participants were using ≤1 medication at final follow-up. No serious complications were reported across studies utilizing the iTrack or OMNI systems.
 
In 2022, NICE published an interventional procedures guidance on ab interno canaloplasty for open-angle glaucoma (NICE, 2022). The current recommendation states that "evidence on the safety of ab interno canaloplasty for open-angle glaucoma shows no major safety concerns. Evidence on the efficacy is limited in quality and quantity, particularly in the long term. Therefore, this procedure should only be used with special arrangements for clinical governance, consent, and audit or research."
 
2024 Update
Annual policy review completed with a literature search using the MEDLINE database through February  2024. No new literature was identified that would prompt a change in the coverage statement. The key identified literature is summarized below.
 
Other case series have evaluated ab interno canaloplasty via the use of the iTrack (Gallardo, 2022 & Koerber, 2022) or OMNI surgical systems (Murphy, 2022, Ondrejka, 2022 & Gallardo 2022) inpatients with mild-to-moderate primary open-angle glaucoma as a standalone procedure or in combination with cataract surgery. Two studies of the OMNI system evaluating a total of 267 eyes with uncontrolled baseline intraocular pressure (IOP) reported mean reductions in IOP and medication use ranging between 5.5 to 6.4 mmHg and 0.6 to 1.1 medications, respectively, over 12-36 months of follow-up (Ondrejka, 2022 & Murphy, 2022). Results from the smaller GEMINI study of 120 patients treated with the OMNI system reported an IOP reduction of 8.2 mmHg and a mean decrease of 1.4 medications over 12 months, with 75% of participants achieving a mean IOP ≤18 mmHg; however, analysis was based on mean diurnal ocular pressure following medication washout at baseline, and itis unclear what proportion of patients initially had uncontrolled IOP on medication (Gallardo, 202). A subgroup analysis of 39 Hispanic participants in the GEMINI study, a demographic disproportionally affected by primary open-angle glaucoma in the U.S., showed comparable results, with a mean IOP decrease of 7.9 and no need for continued medication use in 87% (Gallardo, 2022). One small study utilizing the OMNI system in 27 patients previously treated with the iStent trabecular micro bypass stent reported a mean IOP reduction of 5.1 mmHg and a mean decrease of 0.4 medications (Terveen, 2022). Two studies of the iTrack system evaluated a total of 71 eyes treated with canaloplasty alone or in combination with cataract surgery and reported 36 to 48 month outcomes (Gallardo, 2022 & Koerber, 2022). Mean IOP reductions ranged from 5.2 to 7.2 mmHg and medication use decreased between 1 to 1.5 medications. Overall, 68.2%% to77.2% of participants were using ≤1 medication at final follow-up. No serious complications were reported across studies utilizing the iTrack or OMNI systems.
 
In 2022, an interventional procedures guidance was published on ab interno canaloplasty for open-angle glaucoma (NICE, 2023). The current recommendation states that "evidence on the safety of ab interno canaloplasty for open-angle glaucoma shows no major safety concerns. Evidence on the efficacy is limited in quality and quantity, particularly in the long term. Therefore, this procedure should only be used with special arrangements for clinical governance, consent, and audit or research."
 
2024 Update
Annual policy review completed with a literature search using the MEDLINE database through March  2024. No new literature was identified that would prompt a change in the coverage statement. The key identified literature is summarized below.
 
A prospective, non-randomized study was reported on that compared the safety and efficacy of iStent bypass implantation (n=69) versus ab externo canaloplasty (n=69) in patients with primary open-angle glaucoma (Golaszewska, 2023). Both procedures were combined with phacoemulsification. All patients were indicated for surgery despite receiving the maximum tolerated pharmacological treatment and in whom glaucoma progression was detected on multiple examinations within the same year. Demographic and clinical characteristics were generally balanced between iStent and canaloplasty groups, including age(mean ± SD, 71.5±9.4 vs. 70.2±6.9 years) and preoperative IOP (18.4±3.9 vs 17.2±4.0 mm Hg). The mean number of antiglaucoma drugs before surgery was significantly higher in the canaloplasty group (2.4±1) than in the iStent group (1.9±0.9;p=.036). No significant differences in IOP (15.5 ± 2.5 vs. 15.0 ± 2.4; p=.48) or the proportion of patients with >20% reduction in IOP (37% in both groups; p>.999) were observed between the iStent and canaloplasty groups. The mean number of antiglaucoma drugs (0.2 ± 0.6 vs. 0.6 ± 1.2) and the rate of medication discontinuation (86% vs. 71.4%) did not vary at 1 year between the iStent and canaloplasty groups. Complications of microhyphema (2.9% vs. 42.3%; p<.001) and elevated IOP (21.7% vs. 50.0%; p=.015) were significantly less common in the iStent group intra-operatively through 14 days post-operatively, but no differences were observed in the rate of late complications.
 
In a GEMINI extension study, 66 participants demonstrated a mean diurnal ocular pressure reduction of6.9 mm Hg from baseline, with 71% maintaining an IOP between 6 and 16 mm Hg and a reduction in mean number of IOP-lowering medications from 1.7 to 0.3 over three years of follow-up (Greenwood, 2023).
 
Yin et al. (2023) reported on an RCT with ab interno canaloplasty (n=38) versus gonioscopy-assisted transluminal trabeculectomy (n=39) in open-angle glaucoma (Yin, 2023). Participants had medically uncontrolled or not sufficiently lowered intraocular pressure but no prior history of incisional ocular surgery. Demographic and clinical characteristics were balanced between canaloplasty and tabeculotomy groups, including age (mean ± standard deviation [SD], 41±3 vs. 41±15 years), % severe glaucoma (35.1% vs. 50%), mean preoperative IOP (24.9±10 vs 25.6±10.1 mm Hg), and mean number of IOP lowering medications (3.2±0.9; vs 3.3±0.9). The primary endpoint was the difference in mean IOP and the number of medications used with a secondary outcome of complete surgical success, defined as no additional glaucoma surgery, IOP between 6 and 21mmHg, and no IOP lowering medication usage at 12 months follow-up. Outcome data at the 12-month follow-up was available for 71 participants (92.2%). The study met its primary efficacy endpoint, which showed a superior IOP in the trabeculectomy group (16.0±3.1 mm Hg) over canaloplasty (19.0±5.2; p=.003). No significant between-group differences were observed in threat of freedom from IOP-lowering medications (57.2% in the canaloplasty group vs. 77.8% in the trabeculectomy group; p=.06)or mean glaucoma medication usage (0.9±1.3 in the canaloplasty group vs. 0.6±1.2 in the trabeculectomy group; p=.27) at 1-year follow-up. The 12-month rate of complete surgical success was 56% in the canaloplasty group, and 75% in the trabeculectomy group (p=.09). Three eyes in the canaloplasty group and 1 eye in the trabeculectomy group required additional glaucoma surgeries. Hyphema (87% vs. 47%) and supraciliary effusion (92% vs. 71%) were noted more often in the trabeculectomy group than in the canaloplasty group. No intention-to-treat analysis was performed, and the number of recruited participants was lower than the power calculations recommended. A follow-up of one year limits the assessment of the durability of the treatment effect, and the study took place at a single center in China, which may limit the generalizability of these findings.
CPT/HCPCS:
66174Transluminal dilation of aqueous outflow canal (eg, canaloplasty); without retention of device or stent
66175Transluminal dilation of aqueous outflow canal (eg, canaloplasty); with retention of device or stent
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Klink T, Sauer J, Korber NJ, et al.(2015) Quality of life following glaucoma surgery: canaloplasty versus trabeculectomy. Clin Ophthalmol. 2015;9:7-16. PMID 25565763

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