Ab externo canaloplasty for primary open-angle glaucoma

Evidence-based recommendations on ab externo canaloplasty for primary open-angle glaucoma in adults. This involves widening the eyes main draining canal by inserting a tiny tube, then removing the tube and stitching the canal to keep it open.

# Recommendations
Current evidence on the safety and efficacy of ab externo canaloplasty for primary open-angle glaucoma is adequate to support the use of this procedure provided that standard arrangements are in place for clinical governance, consent and audit.
Ab externo canaloplasty for primary open-angle glaucoma should only be done by clinicians with specific training in the procedure.# Indications and current treatments
Primary open-angle glaucoma is a chronic condition associated with elevated intraocular pressure. It leads to progressive damage to the optic nerve. Early stages are usually asymptomatic but as the condition progresses it causes visual impairment and, if untreated, blindness.
Treatment is usually eye drops containing drugs that either reduce the production of aqueous humor or increase its drainage. Surgical procedures such as trabeculectomy, drainage tubes, deep sclerectomy, viscocanalostomy or laser trabeculoplasty may also be used.# The procedure
Ab externo canaloplasty is a surgical technique that aims to reduce intraocular pressure by improving drainage of aqueous fluid from the eye. It is done under local or general anaesthetic. A superficial hinged flap of sclera is made and a deeper flap excised, exposing the Schlemm's canal. An ultrasound imaging system is used to identify the canal and to visualise the surgical instruments when they are in the canal. A microcatheter with an illuminated tip is introduced into the canal and advanced around its entire circumference. As the catheter tip advances, viscoelastic fluid is injected into the canal to dilate it. When catheterisation of the entire canal is complete a suture is tied to the tip of the microcatheter and it is withdrawn, pulling the suture into the canal. The suture is cut, tied in a loop encircling the inner wall of the canal and tightened. This widens the canal. The superficial flap is sutured.# Efficacy
This section describes efficacy outcomes from the published literature that the committee considered as part of the evidence about this procedure. For more detailed information on the evidence, see the interventional procedure overview.
In a systematic review and meta-analysis of 1,498 eyes, comparing canaloplasty with trabeculectomy, there was no statistically significant difference between groups for complete success rates (maximum postoperative intraocular pressure  of 18 mmHg without medication) and qualified success rates (maximum IOP of 18 mmHg with or without medication) after the procedure. In a case series of 224 patients who had canaloplasty, the complete success rates at 1-, 2- and 3year followup were 44% (64/144), 38% (30/80) and 31% (9/29) respectively, and the qualified success rates were 75% (108/44), 74% (59/80) and 59% (17/29) respectively.
In the systematic review and meta-analysis of 1,498 eyes, the mean IOP reduction was 9.94 mmHg (95% confidence interval  8.42 to 11.45) and was statistically significantly lower in the canaloplasty group (mean difference between groups 3.61, 95% CI 5.53 to 1.69 mmHg) at 1year followup. In a review of 914 eyes treated by canaloplasty alone (n=777 eyes) or with phacoemulsification (n=137 eyes), the mean IOP reduction (after a maximum of 36 months' followup) ranged from 29% to 66% with canaloplasty alone and from 42% to 46% with canaloplasty plus phacoemulsification. In the case series of 224 patients, there was a statistically significant decrease in mean IOP (standard deviation ) from 29.47.9 mmHg before surgery to 16.84.2 mmHg at 1 year, 17.14.7 mmHg at 2 years and 16.93.1 mmHg at 42 months (p<0.0001).
In the systematic review and meta-analysis of 1,498 eyes, the mean reduction in antiglaucoma medication use was 2.11 (95% CI 1.80 to 2.42) 1 year after canaloplasty, and there was no statistically significant difference in medication reduction between groups (mean difference 0.37, 95% CI 0.83 to 0.08). In the review of 914 eyes, mean medication use reduction (after a maximum of 36 months' followup) ranged from 25% to 100% with canaloplasty alone and from 66% to 86% with canaloplasty plus phacoemulsification. In a randomised controlled trial of 59 patients comparing phaco-canaloplasty (n=29) with phaco-non-penetrating deep sclerectomy (n=30), there was a statistically significant decrease in the mean (SD) number of medications used in both groups, from 2.640.68 before surgery to 0.270.67 at 1 year in the phaco-canaloplasty group and from 2.890.94 to 0.550.94 in the phaco-non-penetrating deep sclerectomy group (p<0.05 for the difference within groups, no statistically significant difference between groups).
In a retrospective comparative study of 327 patients who had canaloplasty (n=175) or trabeculectomy (n=152), which collected self-reported questionnaire data 2 years after surgery, the mean score (SD) for satisfaction with results of surgery (ranging from 0, totally discontented, to 10, totally contented) was statistically significantly higher in the canaloplasty group (8.092.71) compared with the trabeculectomy group (7.462.61, p=0.034). In the same study, there were statistically significantly fewer revision surgeries reported in the canaloplasty group (mean number of revision surgeries per patient 0.120.43) compared with the trabeculectomy group (0.671.14, p<0.001). Also, patients were statistically significantly more likely to have a positive mood after canaloplasty (2.300.83) compared with trabeculectomy (1.960.87, p=0.009), stress caused by surgery or followups and treatments was statistically significantly lower with canaloplasty (4.180.86 and 4.360.80 respectively) compared with trabeculectomy (3.591.12 and 3.401.20 respectively; p<0.001), and nonvisual and visual ocular symptoms were statistically significantly lower in the canaloplasty group (p<0.05).
The specialist advisers listed the following key efficacy outcomes: intraocular pressure reduction and reduced use of glaucoma medication.# Safety
This section describes safety outcomes from the published literature that the committee considered as part of the evidence about this procedure. For more detailed information on the evidence, see the interventional procedure overview.
Intraocular pressure (IOP) of more than 30 mmHg after the procedure was reported in 2% to 9% of eyes in a review of 914 eyes treated by canaloplasty alone (n=777 eyes) or by canaloplasty with phacoemulsification (n=137 eyes) at a maximum of 36 months' followup.
Hyphaema (greater than 1 mm layered blood) was statistically significantly more frequent in the canaloplasty group than in the trabeculectomy group at 1year followup, in a systematic review and meta-analysis of 1,498 eyes (odds ratio  9.24, 95% confidence interval  3.09 to 27.60). The incidence of hyphaema in the canaloplasty group was 25% (304/1221). Hyphaema was reported in 23% (7/30) of patients treated by canaloplasty and in 1 patient treated by trabeculectomy within 90 days of the procedure in a randomised controlled trial (RCT) of 62 patients.
Descemet's membrane detachment was only seen in the canaloplasty group, with an incidence of 3% (37/1185) at 1year followup in the systematic review and meta-analysis of 1,498 eyes. Descemet's membrane detachment was reported in 2% to 6% of eyes in the review of 914 eyes at a maximum of 36 months' followup. Microperforation of Descemet's membrane during the procedure was reported in 7% (2/30) of patients treated by canaloplasty in the RCT of 62 patients comparing canaloplasty (n=30) with trabeculectomy (n=32). Trabeculo Descemet's membrane rupture was reported in 1 patient in each group during the procedure in an RCT of 59 patients treated by phaco-canaloplasty (n=29) or phaco-non-penetrating deep sclerectomy (n=30).
Hypotony was statistically significantly less frequent after canaloplasty than after trabeculectomy at 1year followup, in the systematic review and meta-analysis of 1,498 eyes (OR 0.32, 95% CI 0.13 to 0.80). The incidence of hypotony in the canaloplasty group was 9% (94/1091). Flat anterior chamber was reported in 0% to 2% of eyes in the review of 914 eyes, and persistent hypotony was reported in 0% to 1% of eyes.
Central retinal artery occlusion was reported in 1 out of 36 patients in the phaco-canaloplasty group and in none of the patients in the trabeculectomy group in a retrospective comparative study of 77 patients.
Ocular decompression retinopathy was reported in a single case report 1 day after canaloplasty. It was treated with tobramycin and dexamethasone. Three months after canaloplasty, IOP remained in control at 16 mmHg and all retinal haemorrhages had completely resolved.
Choroidal effusion or detachment was statistically significantly less frequent in the canaloplasty group than in the trabeculectomy group, in the systematic review and meta-analysis of 1,498 eyes within 1 year of the procedure (OR 0.25, 95% CI 0.06 to 0.97). Choroidal detachment was reported in 7% (2/29) of patients who had phaco-canaloplasty and in none of the patients who had phaco-non-penetrating deep sclerectomy, in the RCT of 59 patients.
Cataract formation was reported in 0% to 8% of eyes in the review of 914 eyes at a maximum of 36 months' followup.
Anterior synechiae during the procedure was reported in 1 patient treated by canaloplasty in the RCT of 62 patients. It was treated by surgical peripheral iridotomy.
Conjunctival leak incidence was not statistically significantly different between the canaloplasty group and the trabeculectomy group within 1year followup, in the systematic review and meta-analysis of 1,498 eyes (OR 0.72, 95% CI 0.16 to 3.14). Conjunctival leak was reported in 10% (3/30) of patients treated by canaloplasty and in 9% (3/32) of patients treated by trabeculectomy within 90 days of the procedure in the RCT of 62 patients.
Corneal erosion was reported in 1 patient treated by canaloplasty and in 44% (14/32) of patients treated by trabeculectomy within 90 days of the procedure in the RCT of 62 patients.
Detectable conjunctival bleb was reported in 2% (17/899) of patients after canaloplasty, in the systematic review and meta-analysis of 1,498 eyes.
Cells in the anterior chamber after the procedure were reported in 2 patients who had phaco-canaloplasty and in 1 patient who had phaco-non-penetrating deep sclerectomy, in the RCT of 59 patients.
Iris incarceration was reported in 1 patient in each group in the RCT of 59 patients who had phaco-canaloplasty or phaco-non-penetrating deep sclerectomy.
Suture cheese wiring was reported in 0% to 2% of eyes in the review of 914 eyes.
In addition to safety outcomes reported in the literature, specialist advisers are asked about anecdotal adverse events (events which they have heard about) and about theoretical adverse events (events which they think might possibly occur, even if they have never done so). For this procedure, specialist advisers did not list any anecdotal adverse events or theoretical adverse events.# Further information
For related NICE guidance, see the NICE website.
Patient commentary was sought but none was received.

# Information for patients
NICE has produced information on this procedure for patients and carers (information for the public). It explains the nature of the procedure and the guidance issued by NICE, and has been written with patient consent in mind.
ISBN: 978-1-4731-2677-0