Saudi Journal of Ophthalmology
Volume 25, Issue 4 , Pages 329-336, October 2011

A review of canaloplasty

  • Ben J. Harvey, MD
    • ,
  • Mahmoud A. Khaimi, MD

      Affiliations

    • Corresponding Author InformationCorresponding author. Address: Department of Ophthalmology, University of Oklahoma, 608 Stanton L. Young Blvd., Oklahoma City, OK 73104, USA. Tel.: +1 405 271 1093; fax: +1 405 271 6088.

Department of Ophthalmology, Dean McGee Eye Institute, University of Oklahoma, USA

Received 9 July 2011; received in revised form 5 August 2011; accepted 6 August 2011.

Article Outline

Abstract 

Canaloplasty is a method of lowering intraocular pressure (IOP) by which a flexible, beacon-tipped microcatheter equipped with an ophthalmic viscosurgical device (OVD) delivery system is used to catheterize and introduce a suture into Schlemm’s canal. Ligation of this suture provides tension on the canal and facilitates aqueous outflow. Canaloplasty is designed to be a blebless procedure that requires no antifibrotic agents and has been shown to safely and effectively lower IOP in patients with open-angle glaucoma (OAG) with minimal complications. Most importantly, no bleb-related adverse events are associated with this procedure. When contemplating surgical management of OAG, canaloplasty may be considered.

Keywords: Canaloplasty, Trabeculectomy, Schlemm’s canal, Phacoemulsification

 

Back to Article Outline

1. Introduction 

The mainstay of glaucoma treatment is lowering of IOP. The classic treatment algorithm consists of initial medical management followed by incisional glaucoma surgery if necessary with laser therapy sometimes utilized as bridge therapy. Many variations of this paradigm exist. The most popular glaucoma surgery utilized is the trabeculectomy with the use of Mitomycin C, which redirects aqueous from the anterior chamber to a subconjunctival bleb. This procedure, while very effective at lowering IOP, is associated with multiple risks and complications. Intraoperative and postoperative risks include hypotony, hyphema, choroidal detachment and suprachoroidal hemorrhage. The blebs may be associated with bleb leak, bleb encapsulation, bleb dysesthesia, blebitis and bleb-associated endophthalmitis (Greenfield et al., 1996, Prasad and Latina, 2007, Radhakrishnan et al., 2009, Azuara-Blanco and Katz, 1998, Borisuth et al., 1999).

Such complications have encouraged many glaucoma specialists to seek out a less invasive IOP-lowering surgery. Recently circumferential viscodilation and tensioning of Schlemm’s canal using a flexible microcatheter (canaloplasty) in combination with deep sclerectomy has raised interest for the treatment of OAG in adults. The purpose of this review is to present an update on the current status of this procedure.

Back to Article Outline

2. Surgical procedure 

Canaloplasty is a surgery in which Schlemm’s canal is isolated and catherized using a microcatheter equipped with an optical illuminating beacon at its tip and an OVD delivery system. This microcatheter is used to introduce a suture into Schlemm’s canal, which provides enough circumferential tension to distend the canal with the purpose of increasing outflow and decreasing IOP.

A retrobulbar block achieves anesthesia and akinesia preoperatively. The eye is inferoducted after placement of a clear corneal traction suture near the limbus. This may be accomplished with a traditional single-pass or double-pass technique. During the latter, 6-0 or 7-0 polyglactin (Vicryl, Ethicon, Switzerland) is passed perpendicular to the limbus in an anterior-to-posterior direction exiting near the limbus with the first pass. A second pass occurs approximately 2–3 clock-hours away from the initial pass and enters near and perpendicular to the limbus traversing the cornea in a posterior-to-anterior direction. Alternatively, these two passes may be made parallel to the limbus. The exposed Vicryl parallel to the limbus can be used to secure the superficial scleral flap during deep scleral flap creation and canal unroofing.

Canaloplasty begins with a 2–3 clock-hour limbal peritomy followed by exposure of bare sclera accomplished via meticulous dissection of conjunctiva and tenon’s capsule with wetfield cautery used for hemostasis (Fig. 1). Unlike a traditional trabeculectomy procedure, no antifibrotics are necessary. The location of canal entrance may be tailored to fit individual needs. Some surgeons favor a superonasal approach thus sparing the superior and superotemporal conjunctiva should future, more invasive incisional glaucoma surgeries be necessary. Still other surgeons prefer a more conservative inferior approach completely sparing the superior conjunctiva.

Schlemm’s canal can be isolated after dissection of two scleral flaps. The first, superficial flap should be approximately one-third to one-half scleral thickness, and dissection of this flap should be initiated well into clear cornea by approximately one millimeter to allow ample area for creation of the descemetic window (Fig. 2). A 5mm×5mm parabolic or triangular flaps are common techniques employed. This superficial scleral flap may be retracted with the double-pass traction suture described above. Next, a deep scleral flap with a parameter one-half to one millimeter smaller than the superficial flap is fashioned within the base of the previous flap with a dissection plane immediately superficial to the choroid (Fig. 3). Choroidal exposure may occur. Anterior dissection of the deep scleral flap unroofs Schlemm’s canal. Cross striations of the scleral spur serve as anatomic landmarks during creation of the deep flap, as Schlemm’s canal is immediately anterior. Locating this landmark ensures correct depth and plane of dissection.

The eye must now be decompressed in order to decrease the risk of anterior chamber perforation. Paracentesis wound formation with subsequent aqueous release lowers the intraocular pressure to mid-to-high single digits, which is optimal for isolating Schlemm’s canal and creating a trabeculo-descemetic window (TDW) (Fig. 4). After releasing pressure in the anterior chamber the dissection of the deep flap anteriorly isolates Schlemm’s canal. Further dissection in this plane past Schwalbe’s line creates the descemetic window, which should be approximately 500 microns in length (Fig. 5). Aqueous may be seen percolating through the TDW in most but not all cases at this point. Both ostia of the canal are dilated using the iTrack microcatheter (iTrack-250, iScience Interventional, Menlo Park, CA), which is then inserted into one of the ostium. As the microcatheter is inserted into the canal, the lights are dimmed to allow visualization of the illuminating optical fiber beacon through sclera (Fig. 6). If resistance is encountered retract the microcatheter, insert it through the opposite ostium and advance. After successful 360° cannulation of Schlemm’s canal a 9-0 or 10-0 polypropylene suture (Prolene, Ethicon, Switzerland) is tied to the tip of the microcatheter, which is then retracted thus introducing the suture throughout the circumference of the canal (to the authors’ knowledge, no studies have compared 9-0 to 10-0 Prolene; however, it has been reported that 10-0 is more effective at distending Schlemm’s canal and lowering IOP when compared with 6-0 Prolene (Grieshaber et al., 2010c). While retracting the microcatheter ophthalmic viscosurgical device (OVD) is injected into the canal at a rate of 0.5μL/2h or 1/8th turn of the OVD injector every 2 clock-hours. The suture is removed from the microcatheter and carefully tied to allow adequate tension on Schlemm’s canal while avoiding inadvertent trabeculotomy. Adequate suture tension is paramount to achieve proper 360° distension of Schlemm’s canal.

The deep scleral flap is excised followed by water-tight closure of the superficial flap with interrupted 10-0 nylon sutures. Alternatively, the superficial flap may be left unsutured if no flow is noted. Tenon’s capsule and conjunctiva are closed with 8-0 Vicryl at the limbus, and the surgery is concluded with injection subconjunctival antibiotics and application of topical antibiotic-steroid ointment.

Back to Article Outline

3. Canaloplasty combined with cataract surgery 

Combining cataract and glaucoma surgery is often necessary, as glaucoma surgery can cause cataract progression (AGIS Investigators, 2001). In addition, cataract surgery alone has been shown to lower IOP anywhere from 1 to 5mmHg (Shingleton et al., 2006, Hayashi et al., 2001, Mathalone et al., 2005). Furthermore, phacocanaloplasty shows a lower IOP trend than canaloplasty alone (Lewis et al., 2011); therefore, combining the two has gained popularity.

Cataract surgery may be combined with canaloplasty with simple adjustments or steps added during the procedure. Phacoemulsification ensues prior to canaloplasty using the surgeons preferred techniques. A side port incision is made followed by introduction of OVD into the anterior chamber. Size, shape and relative location of clear corneal incisions may vary, but keep in mind that both side port and clear corneal incisions must be placed in a manner as to not intersect the corneal traction suture that will be necessary at the beginning of canaloplasty. When operating on either eye, both incisions may be skewed inferotemporally to avoid such complications. Complete and thorough removal of OVD is key to avoid postoperative IOP spikes, which may be detrimental to glaucoma patients. Finally, the clear corneal incision is sutured in order to maintain anterior chamber stability during canaloplasty, which is then performed using the technique previously described above.

Back to Article Outline

4. Postoperative care 

Postoperatively, patients are placed on a low-dose steroid and a third or fourth generation fluoroquinolone drop three-to-four times per day. The steroid drop must be weaned quickly, preferably within two weeks, as we have found a more pronounced steroid response in patients undergoing canaloplasty. This anecdotal data may be at least partially attributed to the OAG patient population who are at higher risk for steroid response (Kersey and Broadway, 2006); however, other factors may be contributing to this phenomenon after the trabeculocanalicular outflow system alteration occurs via canaloplasty. Relative incidence and etiology of steroid response post canaloplasty have yet to be fully investigated.

Back to Article Outline

5. Discussion 

The most comprehensive evaluation of canaloplasty was performed by Lewis et al. (2011) in their 3-year international multicenter prospective study. Patients were included if they had OAG and a baseline IOP of ⩾16mmHg and a historical IOP of ⩾21mmHg. Angle-closure glaucoma (primary or secondary), uveitic glaucoma and angle recession glaucoma patients were excluded. Patients who underwent more than two laser trabeculoplasties were also excluded. At three years, the mean postoperative IOP for all eyes (n=157) was decreased from 23.8±5.0mmHg on 1.8±0.9 medications to 15.2±3.5mmHg on 0.8±0.9 medications demonstrating a 36.1% IOP decrease from baseline. These patients were divided into subsets for subsequent analysis. Overall, successful tensioning suture placement occurred in 84.7% of patients (n=133). Successful suture placement within Schlemm’s canal after canaloplasty alone was performed in 103 eyes with 36-month data available for 89 eyes. Of this subset, there was a 34% IOP decrease from baseline from 23.5±4.5mmHg on 1.9 ± 0.8 medications to 15.5±3.5mmHg on 0.9±0.9 medications at 36months. Canaloplasty with successful suture placement combined with phacoemulsification was performed in 30 eyes with 36-month data available for 27 eyes. Baseline IOP decreased from 23.5±5.2mmHg on 1.5±1.0 medications to 13.6±3.6mmHg on 0.3±0.5 medications at 36months postoperatively accounting for a 42.1% reduction. There was a trend for lower IOP after phacocanaloplasty versus canaloplasty, but this difference was not significant (p=0.95). Intraocular pressure in the low teens has been reported in other studies as well following the combined procedure (Bull et al., 2011, Shingleton et al., 2008). In all groups, the IOP and medication use was significantly decreased at all time intervals compared to baseline (p<0.001).

Lewis et al. (2009) further delineated response to canaloplasty based on degree of canal distension. Using high-resolution anterior segment ultrasound biomicroscopy (UBM) analyzed before, during and after surgery the investigators were able to develop a grading system of suture tension on Schlemm’s canal. Application of this scale allowed objective evaluation of canal distension and its effect on postoperative IOP reduction in eyes that received canaloplasty alone. These eyes were divided into discernable or no discernable distension with the former showing a 31% IOP decrease and the latter showing a 20% IOP decrease exemplifying a significantly exaggerated IOP-lowering response at 24months in eyes with effective suture tensioning on Schlemm’s canal (p=0.018).

Another long-term study investigated the efficacy of canoloplasty and phacocanaloplasty on European eyes with open-angle glaucoma (Bull et al., 2001). One hundred and nine eyes were included in the study with successful intracanalicular suture tensioning occurring in 98 eyes (89.9%), canaloplasty alone performed in 93 eyes (85.3%) and phacocanaloplasty performed in 16 eyes (14.7%) with 3-year follow-up data available for 96 eyes (88.1%). In the canaloplasty alone group the mean baseline IOP of 23.0±4.3mmHg on an average 1.9±0.7 medications was significantly reduced to 15.1±3.1mmHg on 0.9±0.9 medications while the phacocanaloplasty group’s mean baseline IOP of 24.3±6.0mmHg on an average 1.5±1.2 medications was significantly reduced to 13.8±3.2mmHg on 0.5±0.7 medications (p<0.00001).

Grieshaber et al. (2011) published a series with similar results. Thirty-two white patients with open angles, IOP>21mmHg, glaucomatous optic neuropathy and corresponding visual field defects who underwent canaloplasty were included in this study. Patients were excluded if they received previous ocular surgery or laser. Complete success (IOP reduction without medications) occurred in 93.8% with IOP⩽21, 84.4% with IOP⩽18, and 74.9% with IOP⩽16 12 months postoperatively. Before canaloplasty, the mean IOP and number of medications were 27±5.6mmHg and 2.7±0.5 medications, respectively. Eighteen months after canaloplasty the mean IOP and number of medications were 13.1±1.2mmHg and 0.1±0.3 medications, respectively.

While the aforementioned patients were primarily white, canaloplasty appears to be effective in black and Asian populations as well. Grieshaber et al. (2010a) also published long-term data with a mean follow-up of 30.6±8.4months on canaloplasty performed on black Africans, the majority of which (98%) received canaloplasty as primary glaucoma treatment. In this study, 60 consecutive POAG patients were selected to receive canaloplasty. The mean preoperative IOP was 45.0±12.1mmHg. At 6, 12, 24 and 36months postoperatively the mean IOP without medications was 15.4±5.4mmHg (n=57), 15.4 ± 5.2mmHg (n=54), 16.3 ± 4.2mmHg (n=51), and 13.3±1.7mmHg (n=49), respectively. Complete success defined as IOP⩽21mmHg without medications was achieved in 77.5%, and qualified success (IOP⩽21mmHg with or without medications) was seen in 81.6% of patients at 36months. Ninety-five percent of patients had no deterioration of Snellen visual acuity at 36months.

A small case series of Japanese patients receiving canaloplasty or phacocanaloplasty is also present in the literature (Fujita et al., 2011). In this study 11 eyes of 9 Japanese patients with POAG underwent canaloplasty (three eyes) or phacocanaloplasty (eight eyes). The mean preoperative IOP was 23.4±5.5mmHg on 2.8±0.6 medications. At 1, 3, 6 and 12months the mean IOP was 13.7±2.8mmHg, 12.8±3.5mmHg, 14.0±4.4, and 15.0±4.1, respectively. The mean postoperative medications significantly decreased to 1.2±0.8 (p<0.01). A qualified success rate with and IOP⩽21, 18 or 16mmHg with or without medications at 12months was achieved in 81.8, 54.5 and 54.5%, respectively.

Back to Article Outline

6. Adverse events 

When compared to trabeculectomy, canaloplasty offers a more favorable side effect profile; however, one must be aware of potential complications encountered during or after this procedure. Intraoperative complications include inability to cannulate Schlemm’s canal, Descemet membrane detachment and improper microcatheter passage (Lewis et al., 2011, Bull et al., 2011, Shingleton et al., 2008, Lewis et al., 2009, Grieshaber et al., 2011, Grieshaber et al., 2010a, Fujita et al., 2011). Successful 360° cannulation of Schlemm’s canal with intracanalicular suture placement was see in 84.7% of eyes in Lewis’s 3-year study and 74–89.9% in other studies (Lewis et al., 2011, Bull et al., 2011, Shingleton et al., 2008). Unsuccessful 360° catheterization was usually attributed to early surgical inexperience or anatomical obstacles (Lewis et al., 2011, Shingleton et al., 2008). All but one eye had successful cannulation and suturing of SC in Grieshaber’s studies (Grieshaber et al., 2011, Grieshaber et al., 2010a). No cannulation issues were reported in Fujita’s case series (Lewis et al., 2009). Descemet membrane detachment rate was uncommon, ranging from 1.6% to 9.1% (Lewis et al., 2011, Bull et al., 2011, Shingleton et al., 2008, Lewis et al., 2009, Grieshaber et al., 2011, Grieshaber et al., 2010a, Fujita et al., 2011) (Fig. 7). One case report described bilateral descemet membrane detachment in one patient who underwent consecutive canaloplasty in each eye (Palmiero et al., 2010), and another described an intracorneal hematoma following a proposed intraoperative descemet membrane detachment (Gismondi and Brusini, 2011). In rare settings, the microcatheter could exit SC and violate surrounding structures. This occurred in two patients (3.3%) of Grieshaber’s black Africans receiving canaloplasty. The microcatheter entered the anterior chamber in one patient and the suprachoroidal space in another. In both instances the microcatheter was retracted and successful cannulation ensued. Passage of the microcatheter into the suprachoroidal space created a presumed ‘microcyclodialysis’ with subsequent hypotony that spontaneously resolved. Breaking through the TM into the anterior chamber may have introduced excess OVD with a resultant hypertensive phase, which was successfully treated with a short course of oral acetazolamide (Grieshaber et al., 2010a). Intraoperative trans-TM suture extrusion occurred in one eye (0.8%) in Lewis et al. (2011) study.

Hyphema or microhyphema (defined differently by different authors) were the most common post canaloplasty complications with a wide range of reported events depending on qualifying parameters. Collectively, hyphemas and microhyphemas ranged from 6.1% to 70% of eyes. All events were transient and resolved without sequela with most resolving by one week and all resolving by one month in every study (Lewis et al., 2011, Bull et al., 2011, Shingleton et al., 2008, Lewis et al., 2009, Grieshaber et al., 2011, Grieshaber et al., 2010a, Fujita et al., 2011). Another common side effect noted in Lewis’s and Bull’s 3-year studies was cataract formation with 12.7% and 19.1% developing visually significant cataracts, respectively (Lewis et al., 2011; Bull et al., 2001). Conversely, Grieshaber’s 3-year study demonstrated only a temporary decline in VA, which returned to baseline in 95% of patients (Grieshaber et al., 2010a). Some eyes experienced an unexpected increase in pressure. Intraocular pressure elevation ⩾30mmHg occurred in 1.6–18.2% of eyes, which was thought by some authors to be secondary to retained viscoelastic in the anterior chamber. Persistent elevation in IOP requiring laser goniopuncture was necessary in 8.3–18.8% in some studies; however, in other reports no eyes required laser goniopuncture. Other postoperative complications reported in the literature include suture ‘cheese-wiring’ through the TM (up to 9.1%), wound hemorrhage (up to 2.5%) and hypotony (up to 0.6%) Lewis et al., 2011, Bull et al., 2011, Shingleton et al., 2008, Lewis et al., 2009, Grieshaber et al., 2011, Grieshaber et al., 2010a, Fujita et al., 2011. Bleb formation occurred in only 2.5% of Lewis’s patients and none of Grieshaber’s patients at 36months (Lewis et al., 2011, Grieshaber et al., 2010a). Of note, no choroidal detachment, suprachoroidal hemorrhage, blebitis or bleb-associated endophthalmitis has been reported in the literature to date.

Back to Article Outline

7. Contraindications 

Contraindications for canaloplasty include patients with chronic angle closure, narrow angles, angle recession, neovascular glaucoma and in eyes that have undergone previous glaucoma procedures that preclude adequate cannulation of Schlemm’s canal (Godfrey et al., 2009). Chronic angle closure causes increased intraocular pressure by obstructing the trabecular meshwork with the peripheral iris with subsequent development of peripheral anterior synechiae (PAS). Such obstruction is upstream from Schlemm’s canal; therefore, canaloplasty may be ineffective. Similarly neovascular glaucoma covers the TM with a neovascular membrane that eventually contracts leading to the development of PAS and secondary angle closure. Uveitic glaucoma may develop secondary to obstruction of the TM with inflammatory debris or secondary to inflammation-induced PAS formation. Procedures that may prevent adequate cannulation of Schlemm’s canal include (but are not limited to) trabeculectomy, trabeculotomy, goniotomy, argon laser trabeculoplasty (ALT), trabectome (NeoMedix Inc., Tustin, California, USA), iStent® Trabecular Micro-Bypass (Glaukos Corp., Laguna Hills, California, USA), and Eyepass Glaucoma Implant (GMP Companies Inc., Fort Lauderdale, Florida, USA). Trabeculotomy, either ab externo or ab interno, and goniotomy violate the inner wall of Schlemm’s canal; therefore, adequate tension may not be distributed to the canal. Similarly, the trabectome, which uses an electrocautery tip to remove portions of the TM and the inner wall of Schlemm’s canal removes the essential anatomy required in canaloplasty. ALT may cause extensive scarring which can obstruct circumferential cannulation of the canal (Godfrey et al., 2009, Mosaed et al., 2009). The Micro-Bypass implants themselves may block microcatheter advancement. Additionally, success of canaloplasty may be limited if aqueous outflow channels distal to the canal are collapsed or scarred. Some authors have described intraoperative injection of fluorescein into Schlemm’s canal via the microcatheter enabling in vivo visualization of the aqueous outflow system (channelography), which may elucidate the outflow capacity and predict how a patient may respond to canaloplasty (Grieshaber et al., 2009). These implications have yet to be validated.

Back to Article Outline

8. Ideal pt selection 

Ideal patient selection is key when considering canaloplasty. Patients with mild-to-moderate open-angle glaucoma with an IOP goal in the low-to-mid teens would benefit greatly from canaloplasty. In addition, advanced glaucoma may be treated with canaloplasty in patients who are not suitable for trabeculectomy. For example, those who cannot adhere to the rigorous postoperative care required after trabeculectomy may undergo canaloplasty instead as the follow-up appointments and postoperative drops are less frequent. In eyes with thin conjunctiva that may be at higher risk for bleb leaks after trabeculectomy with mitomycin C, canaloplasty may be the preferred procedure (Borisuth et al., 1999). Conversely, young black patients with more robust scar formation should undergo canaloplasty if bleb failure secondary to scarring is of concern (Broadway et al., 1994, The Advanced Glaucoma Intervention Study, 2001, Ederer et al., 2004). One may consider combining phacoemulsification with canaloplasty if a visually significant or early visually significant cataract surgery is anticipated in the near future or if a phacomorphic glaucoma component exists. Phacocanaloplsty has also been shown to lower IOP more than canaloplasty alone (Lewis et al., 2011). Due to the low side effect profile and efficacy of canaloplasty, it may be strongly considered in monocular patients with OAG as well thereby sparing the patient the lifelong bleb-related risks. Far less hypotony is seen after canaloplasty as opposed to trabeculectomy (0.6% versus 42.3%), so the former should be considered in young myopic individuals who are at an increased risk for hypotony maculopathy (Fannin et al., 2003).

Back to Article Outline

9. Conclusion 

Canaloplasty has been shown in the literature to be a viable alternative to more traditional incisional glaucoma surgery. Viscodilating Schlemm’s canal using a flexible, beacon-tipped microcatheter with subsequent suture tensioning is designed to be a blebless procedure that requires no antifibrotic agents and has been suggested to restore the natural outflow system of the eye (Khaimi, 2009). Canaloplasty targets the pathologic site of maximal aqueous outflow resistance in open-angle glaucoma theoretically by stretching Schlemm’s canal and adjacent juxtacanalicular outflow system, and a pilocarpine-like effect on the TM may occur as well (Lewis et al., 2011, Grieshaber et al., 2010a). The effect of suture tensioning may actually alter the anatomical structure of the TM to favor aqueous outflow over time. This and/or delayed re-opening of distal collector channels has been proposed to offer mild, late IOP reduction remotely after surgery (Grieshaber et al., 2010a). Canaloplasty has repeatedly been shown to be safe and effective at significantly lowering IOP and medication dependence in different patient populations with OAG. Whites, blacks and select Asian populations respond similarly to canaloplasty making this procedure favorable for many races despite the more robust scar tissue formation seen in blacks or the narrower angle anatomy seen in Asians. Furthermore, Cox regression analyses in select studies have identified no preoperative predictors of IOP after surgery including preoperative IOP, gender and age (Lewis et al., 2011, Grieshaber et al., 2011, Grieshaber et al., 2010a, Fujita et al., 2011). In fact, stark differences in preoperative IOP of patients receiving canaloplasty alone in Lewis’s and Grieshaber’s 3-year studies still yielded similar mean postoperative IOP. The former had a mean preoperative IOP of 23.5±4.5mmHg while the latter had a mean preoperative IOP of 45.0±12.1mmHg. Despite this disparity, the resultant mean postoperative IOPs were similar in each study (15.5±3.5mmHg and 13.3±1.7mmHg). This may represent the inability of canaloplasty to overcome episcleral venous pressure thus limiting IOP reduction below 12mmHg (Grieshaber et al., 2010a).

We believe that canaloplasty offers a more favorable safety profile when compared with trabeculectomy. Hyphema or microhyphema were by far the most common complications reported in the major canaloplasty literature to date. Some authors posit hyphemas are signs of surgical success after canaloplasty conveying re-establishment of a patent natural outflow system as red blood cells driven by episcleral venous pressure egress out of the canal, through the TM and into the anterior chamber (Grieshaber et al., 2010a, Grieshaber et al., 2010b). One but not all studies had an increase in cataract formation 3years after canaloplasty. Lewis et al. listed cataract formation as the most common late postoperative complication 3years after canaloplasty occurring in 12.7%; however, this was not the case in Grieshaber’s 3year follow-up on black Africans post canaloplasty. Perhaps the increased cataract formation in Lewis’s study can be attributed to age-related changes rather than changes related to the surgery, as Lewis’s patients were on average older than Grieshaber’s black African patients (67±11.6years versus 49.8 ± 15.7years) (Lewis et al., 2011, Grieshaber et al., 2010a). Cataract progression after canaloplasty is still less frequent than after trabeculectomy, which has been reported to increase the risk of cataract formation by 47% (AGIS Investigators, 2001). Hypotony after canaloplasty was reported in 0.6% of a predominantly white population (91.7%) (Lewis et al., 2011). This percentage is far more favorable than the incidence of hypotony in whites after trabeculectomy, which has been reported to be as high as 13.8% (Borisuth et al., 1999). Probably the most significant advances canaloplasty offers are the lack of choroidal detachments, suprachoroidal hemorrhage, blebitis or bleb-related endophthalmitis observed in any eyes treated with canaloplasty or phacocanaloplasty (Lewis et al., 2011, Bull et al., 2011, Shingleton et al., 2008, Lewis et al., 2009, Grieshaber et al., 2011, Grieshaber et al., 2010a, Fujita et al., 2011, Khaimi, 2009). Canaloplasty is designed to be a blebless procedure, and in fact, only 2.5% of patients developed blebs (Lewis et al., 2011). However, no bleb-related complications resulted. The incidence of bleb-associated endophthalmitis has been reported in 0.2–9.6% of patients after trabeculectomy, which increases to 2.5% per patient-year with the addition of mitomycin C (Greenfield et al., 1996, Prasad and Latina, 2007).

In summary, canaloplasty has become an appealing alternative to traditional incisional glaucoma therapies. It is less invasive, blebless, no mitomycin C is necessary. While canaloplasty is effective in lowering IOP and medication dependence, it still has its limitations. It may be contraindicated in patients with chronic angle closure, narrow angles, angle recession, neovascular glaucoma and in eyes that have undergone previous glaucoma procedures that preclude adequate canulation of Schlemm’s canal. If pressure lowering below mid-to-low teens is desired then a trabeculectomy with antifibrotics or glaucoma drainage implant may be preferred over canaloplasty, which may not be the best option in patients with advanced glaucoma in need of very low IOP. There is a learning curve for successful catheterization of Schlemm’s canal, and certain anatomical variations may prohibit successful catheterization such as the microcatheter tip entering a large collector channel or meeting unknown resistance (Lewis et al., 2011). The pressure-lowering effects and the relatively low side effect profile of canaloplasty appear sound, but this must be weighted against traditional measures. Mosaed et al. (2009) published a literature review comparing trabeculectomy, glaucoma drainage devices, trabectome and canaloplasty claiming trabeculectomy is ‘the most effective IOP-lowering procedure to date’. There was, however, no standardization amongst the different studies analyzed nor were any of the procedures directly compared. Canaloplasty has only been directly compared to viscocanalostomy in a retrospective case series, which determined the former to be more efficacious than the latter (Koerber, 2011). Recently the American Academy of Ophthalmology commissioned the Ophthalmic Technology Assessment Committee Glaucoma Panel to review the available literature on the efficacy of novel glaucoma procedures including canaloplasty. The panel concluded that with the current data it is impossible to state canaloplasty or other novel glaucoma procedures are superior, inferior or equal to traditional glaucoma surgeries or to each other (Francis et al., 2011). Ultimately, randomized clinical trials comparing canaloplasty to traditional and other novel glaucoma procedures with standardized definitions of success and failure, inclusion and exclusion criteria and follow-up period are required to determine its efficacy. Future studies are also needed to explore the long-term effects of canaloplasty on IOP and the remote side effects of this procedure; however, currently canaloplasty appears to be a valuable tool in the armamentarium of glaucoma procedures.

Back to Article Outline

Conflict of interest statement 

We have no conflict of interest to declare.

Back to Article Outline

References 

  1. The Advanced Glaucoma Intervention Study (AGIS), 2001. 9. Comparison of glaucoma outcomes in black and white patients within treatment groups. Am. J. Ophthalmol. 132, 311–320.
  2. AGIS Investigators.Gaasterland DE, Blackwell B, Ederer F, et al. The Advanced Glaucoma Intervention Study; 8: risk of cataract formation after trabeculectomy. Arch. Ophthalmol. 2001;119:1771–1779
  3. Azuara-Blanco A, Katz LJ. Dysfunctional filtering blebs. Surv. Ophthalmol. 1998;43:93–126
  4. Borisuth NSC, Phillips B, Krupin T. The risk profile of glaucoma filtration surgery. Curr. Opin. Ophthalmol. 1999;10:112–116
  5. Broadway D, Grierson I, Hitchings R. Racial differences in the results of glaucoma filtration surgery: are racial differences in the conjunctival cell profile important?. Br. J. Ophthalmol. 1994;78:466–475
  6. Bull, H., von Wolff, K., Korger, N., Tetz, M., 2011. Three-year canaloplasty outcomes for the treatment of open-angle glaucoma: European study results. Graefes Arch. Clin. Exp. Ophthalmol. (Epub ahead of print).
  7. Ederer F, Gaasterland DA, Dally LG, et al. The Advanced Glaucoma Intervention Study (AGIS). Ophthalmology. 2004;111:651–664
  8. Fannin LA, Schiffman JC, Budenz DL. Risk factors for hypotony maculopathy. Ophthalmology. 2003;110:1185–1191
  9. Francis BA, Singh K, Lin SC, Hodapp E, Jampel HD, Samples JR, et al. Novel glaucoma procedures: a report by the American academy of ophthalmology. Ophthalmology. 2011;118:1466–1480
  10. Fujita K, Kitagawa K, Ueta Y, Nakamura T, Miyakoshi A, Hayashi A. Short-term results of canaloplasty surgery for primary open-angle glaucoma in Japanese patients. Case Rep. Ophthalmol. 2011;2:65–68
  11. Gismondi M, Brusini P. Intracorneal hematoma after canaloplasty in glaucoma. Cornea. 2011;30:718–719
  12. Godfrey DG, Fellman RL, Neelakantan A. Canal surgery in adult glaucomas. Curr. Opin. Ophthalmol. 2009;20:116–121
  13. Greenfield DS, Suner IJ, Miller MP, Kangas TA, Palmberg PF, Flynn HW. Endophthalmitis after filtering surgery with mitomycin. Arch. Opthalmol. 1996;114(8):943–949
  14. Grieshaber MC, Pienaar A, Olivier J, Stegmann R. Channelography: imaging of the aqueous outflow pathway with flexible microcatheter and fluoroscein in canaloplasty. Klin. Monatsbl. Augenheilkd. 2009;226:245–248
  15. Grieshaber MC, Pienaar A, Olivier J, Stegmann R. Canaloplasty for primary open-angle glaucoma: long-term outcome. Br. J. Ophthalmol. 2010;94:1478–1482
  16. Grieshaber MC, Pienaar A, Olivier J, Stegmann R. Clinical evaluation of the aqueous outflow system in primary open-angle glaucoma for canaloplasty. Invest. Ophthalmol. Vis. Sci. 2010;51:1498–1504
  17. Grieshaber MC, Pienaar A, Olivier J, Stegmann R. Comparing two tensioning suture sizes for 360o viscocanalostomy (canaloplasty): a randomized controlled trial. Eye. 2010;24:1220–1226
  18. Grieshaber MC, Fraenkl S, Schoetzau A, Flammer J, Orgul S. Circumferential viscocanalostomy and suture canal distension (canaloplasty) for Whites with open-angle glaucoma. J. Glaucoma. 2011;20:298–302
  19. Hayashi K, Hayashi H, Nakao F, Hayashi F. Effect of cataract surgery on intraocular pressure control in glaucoma patients. J. Cataract Refract. Surg. 2001;27:1779–1786
  20. Kersey JP, Broadway DC. Corticosteroid-induced glaucoma: a review of the literature. Eye. 2006;20:407–416
  21. Khaimi MA. Canaloplasty using iTrack 250 microcatheter with suture tensioning on Schlemm’s canal. Middle East Afr. J. Opthalmol. 2009;19:127–129
  22. Koerber, N.J., 2011. Canaloplasty in one eye compared with viscocanalostomy in the contralateral eye in patients with bilateral open-angle glaucoma. J. Glaucoma (Epub ahead of print).
  23. Lewis RA, von Wolff K, Tetz M, Koerber N, Kearney JR, Shingleton BJ, et al. Canaloplasty: circumferential viscodilation and tensioning of Schlemm’s canal using a flexible microcatheter for the treatment of open-angle glaucoma in adults: two-year interim clinical study results. J. Cataract Refract. Surg. 2009;35:814–824
  24. Lewis RA, von Wolff K, Tetz M, Koerber N, Kearney JR, Shingleton BJ, et al. Canaloplasty: three-year results of circumferential viscodilation and tensioning of Schlemm’s canal using a microcatheter to treat open-angle glaucoma. J. Cataract Refract. Surg. 2011;37:682–690
  25. Mathalone N, Hyam M, Neiman S, Buckman G, Hod Y, Geyer O. Long-term intraocular pressure control after clear corneal phacoemulsification in glaucoma patients. J. Cataract Refract. Surg. 2005;31:479–483
  26. Mosaed S, Dustin L, Minckler DS. Comparative outcomes between newer and older surgeries for glaucoma. Trans. Am. Ophthalmol. Soc. 2009;107:127–135
  27. Palmiero PM, Aktas Z, Lee O, Tello C, Sbeity Z. Bilateral descemet membrane detachment after canaloplasty. J. Cataract Refract. Surg. 2010;36:508–511
  28. Prasad N, Latina MA. Blebitis and endophthalmitis after glaucoma filtering surgery. Int. Ophthalmol. Clin. 2007;47:850–897
  29. Radhakrishnan S, Quigley HA, Jampel HD, Friedman DS, Ahmad SI, Congdon NG, et al. Outcomes of surgical bleb revision for complications of trabeculectomy. Ophthalmology. 2009;116:1713–1718
  30. Shingleton BJ, Paternack JJ, Hung JW, O’Donoghue MW. Three and five year changes in intraocular pressure after clear corneal phacoemulsification in open angle glaucoma patients. J. Glaucoma. 2006;15:494–498
  31. Shingleton B, Tetz M, Korber N. Circumferential viscodilation and tensioning of Schlemm canal (canaloplasty) with temporal clear corneal phacoemulsification cataract surgery for open-angle glaucoma and visually significant cataract: one-year results. J. Cataract Refract. Surg. 2008;34:433–440

PII: S1319-4534(11)00106-8

doi:10.1016/j.sjopt.2011.08.003

Saudi Journal of Ophthalmology
Volume 25, Issue 4 , Pages 329-336, October 2011

Article Tools

* Image Usage & Resolution