BCBSMT may consider canaloplasty medically necessary as a method to reduce intraocular pressure in patients with chronic primary open-angle glaucoma under the following conditions:
analoplasty experimental, investigational and unproven under all other conditions, including angle-closure glaucoma.
- 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.
Viscocanalostomy is considered experimental, investigational and unproven.
A 2010 meta-analysis by Chai and Loon compared the safety and efficacy of viscocanalostomy with the gold standard of trabeculectomy. 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 six months to four 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 six 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.
One of the studies included in the systematic review was a randomized trial with four-year follow-up by Gilmour et al. from 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 five 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 one 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 three 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. 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 one and three days, one and two 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 two groups (96% for trabeculectomy and 92% for viscocanalostomy). Although trabeculectomy had a greater IOP-lowering effect, there were fewer complications with viscocanalostomy (one microperforation of Descemet’s membrane compared with four cases of shallow anterior chamber and five cases of hypotony with IOP < 4 mm Hg).
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. 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 three-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, six of which resolved by three months. The study design included five-year follow-up. These results were limited by the lack of randomization and high loss to follow-up.
Lewis et al. reported two-year and three-year results from the multicenter study in 2009 and 2011, respectively. 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 three 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 three 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; four eyes (3%) were on three or more antiglaucoma medications, and 66 eyes (49.3%) were on no medications. Another seven patients (4.4%) had additional glaucoma surgery. Six eyes lost two 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 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 one-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). 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 one 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, three 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 six 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 one 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. 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 two 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.
Grieshaber et al. reported a prospective series of 60 consecutive black South African patients with POAG who underwent canaloplasty. 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 three 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. 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 August 2011 found two randomized trials comparing canaloplasty to trabeculectomy. Both studies (NCT01228799 and NCT00854256) are expected to enroll 60 subjects with completion in 2012.
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). 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.
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 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. 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 six 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.
Recently, positive two- to three-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 clinical input, evidence is sufficient for canaloplasty to be considered medically necessary 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.
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 pressure-lowering effect than viscocanalostomy. Although trabeculectomy is associated with greater postoperative risk, most of the adverse events are mild and reversible. Reduction in IOP has also been shown to be greater with canaloplasty than viscocanalostomy in a small within-subject comparison. The clinical input for viscocanalostomy was mixed. Overall, evidence is insufficient to evaluate health outcomes with this procedure in comparison with currently accepted alternatives. Therefore, viscocanalostomy is considered experimental, investigational and unproven.
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