Ab-Interno Canaloplasty

The New Optimal Treatment for Open-Angle Glaucoma? by Konstantin Yakimchuk

Glaucoma surgery continues its metamorphosis . . .

Open-angle glaucoma remains a severe health issue affecting the quality of life of patients and their families. Fortunately, the evolution of surgical methods for the treatment of glaucomatous patients has led to the development of novel non-invasive forms of glaucoma surgery.

The evolution of glaucoma surgeries

Currently, the standard surgical treatment for medically resistant openangle glaucoma is trabeculectomy. However, this procedure possesses severe adverse effects to patients, including scar formation, wound leakage, hypotension and detachment of the choroid. 1 To confront these complications, canaloplasty — a novel surgical method by viscodilation and tensioning of Schlemm’s canal — has been developed.

Traditional canaloplasty has been designed to viscodilate the trabecular meshwork and Schlemm’s canal to repair outflow. 2,3 This surgery is recommended for primary openangle and pseudoexfoliative types of glaucoma. Both the decrease and modulation of intraocular pressure are the main current indicators of the surgical treatment efficacy in patients with glaucoma.

In addition to the original ab-externo canaloplasty, ab-interno canaloplasty (ABiC) is a new step in the ongoing evolution of invasive canaloplasty for glaucoma. 4 How unique is this novel technique? In contrast to the original canaloplasty, the ab-interno technique does not apply tensioning sutures and requires no conjunctival manipulation. Injection of a viscoelastic agent is followed by the insertion of a catheter into the anterior chamber. The next steps of the operation include cutting of the inner layer of Schlemm’s canal with gonioscope, insertion of iTrack into the canal, injection of a viscoelastic agent, and expansion of Schlemm’s canal.

Compared to the standard trabeculotomy, ab-interno (iTrack canaloplasty) has multiple advantages, including effective balancing of intraocular pressure and restoration of aqueous humor drainage mechanisms. Practically, canaloplasty is characterized by minor incision and fast wound regeneration. As to other potential complications, this type of surgery does not cause bleb formation. Furthermore, ab-interno does not influence the incisional glaucoma surgery.

Clinical findings in favor of canaloplasty

Non-penetrating surgery has recently been considered as an effective treatment technique for primary openangle glaucoma, as multiple studies had demonstrated that canaloplasty is effective for reducing intraocular pressure. Earlier published studies have evaluated the benefits of minimally invasive surgery for patients with glaucoma. In particular, the efficacy and safety of canaloplasty and standard trabeculectomy were compared by Liu et al. 5 According to the study, canaloplasty showed better outcomes than standard surgery. Moreover, patients, who underwent canaloplasty, had fewer choroid abnormalities. Canaloplasty with suprachoroidal drainage has been tested on a large cohort of patients. 6 The authors have shown that canaloplasty combined with suprachoroidal drainage reduced intraocular pressure more efficiently than regular canaloplasty. Also, another study has evaluated the outcomes of ab-interno canaloplasty in patients with open-angle glaucoma. 7 The canaloplasty stably decreased the fluid pressure inside the eye within the follow-up period of one year. However, the authors did not observe any reduction of glaucoma medication. In addition, they found that patients with corticosteroidinduced glaucoma would also highly benefit from canaloplasty.

A study by Brusini et al., has shown significant positive effects of canaloplasty on intraocular pressure and reduction of medication during the postoperative period. 8 Another study has demonstrated higher efficiency of canaloplasty combined with trabecular bypass stenting in glaucoma patients when compared to trabecular meshwork bypass. 9

Canaloplasty: Reports from ASCRS Virtual Meeting

Several studies reporting the application of canaloplasty for open-angle glaucoma were presented at the American Society of Cataract and Refractive Surgery (ASCRS 2020) Virtual Annual Meeting this year. Among them, a novel study by Dr. Mark Gallardo 10 has aimed to evaluate the efficacy and safety of canaloplasty in lessening intraocular pressure and glaucoma medications in patients with open-angle glaucoma.

The author compared ab-interno iTrack canal-based surgery as a stand-alone method and canaloplasty combined with cataract extraction. Notably, at two years post-surgery, eye pressure was reduced after both stand-alone canaloplasty and combined surgery, although the decrease of glaucoma medications was greater in the combined method. As to the safety of the surgical procedures, no negative effects were observed. The author has concluded that canaloplasty effectively decreased intraocular pressure and medication need during the 24-month follow-up and can be an effective and

safe technique as either a stand-alone surgery or a combination with cataract extraction.

Also, other studies of canaloplasty were presented by Dr. Mahmoud Khaimi from Dean McGee Eye Institute. One of them has reported that a large cohort of patients was followed after canaloplasty. In line with the studies described above, a significant decrease of intraocular pressure was observed in patients with open-angle glaucoma. 11

According to this study, ab-interno canaloplasty can be effectively used in patients with different types of glaucoma, including cases that are especially hard to treat. Moreover, intraocular pressure was well contained, allowing a decrease of anti-glaucoma therapies.

Another study by Dr. Khaimi has reported the effectiveness of abinterno canaloplasty for pigmentary and pseudoexfoliation glaucoma. 12 The operation was found to be effective for controlling intraocular pressure in patients with these types of glaucoma.

Furthermore, Dr. Juan Carlos Izquierdo has compared the efficacy and safety of canaloplasty alone versus canaloplasty combined with phacoemulsification for the surgical treatment of open-angle glaucoma. 13 Noticeably, both patient groups showed a significant decrease in eye pressure. The author has pointed out that canaloplasty ab-interno can be effectively used to reduce intraocular pressure.

In addition, the impairment of aqueous outflow system in glaucoma patients can be studied by combining iTrack canaloplasty with venography. 14,15 The authors injected trypan blue in vivo into the Schlemm’s canal to visualize the episcleral vein.

Safety, complications and alternatives

Is canaloplasty completely safe? Clearly, ABiC shows fewer complications than other traditional surgical techniques. In fact, most patients report complete recovery within several weeks. Probable intraoperative complications of canaloplasty include damage of Descemet membrane and failure to cannulate Schlemm’s canal. Fluctuations of eye pressure and hyphema were named as potential postoperative complications. 15

Are there any promising alternatives to ABiC? A recent article in the Journal of Glaucoma has suggested a novel suture-probe canaloplasty. 16 The authors used a suture probe to expand Schlemm’s canal and to apply a tensioning suture. Similar to ABiC, the suture-probe canaloplasty reduced intraocular pressure and decreased glaucoma medications. Several postoperative complications, such as microhyphema, bleb leakage and scleral flap lifting, were noted in some patients.

Canaloplasty today and tomorrow

Current minimally invasive techniques provide sufficient reduction of intraocular pressure without notable side effects compared to standard surgical treatment. Recent studies strongly advocate canaloplasty as a superior alternative to trabeculectomy. Ab-interno canaloplasty was proved to be an effective and safe treatment method without adverse effects, such as bleb development and post-operative astigmatism. This technique allows to repair aqueous humor drainage.

Further studies will aim to simplify and optimize the technique. At the same time, broad implementation of canaloplasty might decrease costs of glaucoma therapies, evade adverse effects of standard trabeculectomy, and minimize post-operative procedures.

Editor’s Note:

ASCRS 2020 Virtual Annual Meeting — the world’s first-ever successful virtual ophthalmic conference — was held on May 16 to 17, 2020. Reporting for this article also took place during the virtual ASCRS 2020 conference, where CAKE magazine’s parent company, Media MICE, was the only exhibiting independent media.

REFERENCES:

1 Chou J, Turalba A, Hoguet A. Surgical Innovations in Glaucoma: The Transition From Trabeculectomy to MIGS. Int Ophthalmol Clin. 2017;57(4):39-55.

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16 Lewis RA, et al. Canaloplasty: Circumferential viscodilation and tensioning of Schlemm canal using a flexible microcatheter for the treatment of open-angle glau-coma in adults: Two-year interim clinical study results. J Cataract Refract Surg. 2009;35(5):814-824. Vastardis I, Fili S, Gatzioufas Z, Kohlhaas M. Ab externo canaloplasty results and efficacy: A retrospective cohort study with a 12-month follow-up. Eye Vis (Lond). 2019;6:9. Gallardo MJ, Supnet RA, Ahmed II. K. Viscodilation of Schlemm’s canal for the reduction of IOP via an ab-interno approach. Clin Ophthalmol. 2018;12(10):2149-2155. Liu H, Zhang H, Li Y, Yu H. Safety and efficacy of canaloplasty versus trabeculec-tomy in treatment of glaucoma. Oncotarget. 2017;8(27):44811-44818. Haus A, Szurman P, Seuthe AM. Catheter-independent suture probe canaloplas-ty with suprachoroidal drainage. Graefes Arch Clin Exp Ophthalmol. 2019;257(1):169-173. Davids AM, et al. Ab interno canaloplasty (ABiC)-12-month results of a new min-imally invasive glaucoma surgery (MIGS). Graefes Arch Clin Exp Ophthalmol. 2019;257(9):1947-1953. Brusini P, Tosoni C, Zeppieri M. Canaloplasty in Corticosteroid-Induced Glauco-ma. Preliminary Results. J Clin Med. 2018;7(2):31. Heersink M, Dovich JA. Ab interno canaloplasty combined with trabecular by-pass stenting in eyes with primary open-angle glaucoma. Clin Ophthalmol. 2019;13:1533-1542. Gallardo MJ. 24-Month Outcomes Following Transluminal Viscodilation of Schlemm’s Canal (ab-interno canaloplasty) for the Treatment of Open-Angle Glau-coma. ASCRS Virtual Annual Meeting 16-17 May, 2020. Izquierdo JC, et al. Ab-Interno Canaloplasty Combined with Phacoemulsifica-tion and Ab-Interno Canaloplasty Stand-Alone Procedure in Medically Controlled Glaucoma. ASCRS Virtual Annual Meeting 16-17 May, 2020. Khaimi MA. The Safety and Effectiveness of Ab Interno Canaloplasty in Patients with Narrow-Angle or Chronic Angle-Closure Glaucoma. ASCRS Virtual Annual Meeting 16-17 May, 2020. Khaimi MA. The Effectiveness of Ab Interno Canaloplasty (iTrack) in the Treat-ment of Pigmentary and Pseudoexfoliation Glaucoma. ASCRS Virtual Annual Meet-ing 16-17 May, 2020. Waldner GM, et al. Novel Technique for Treatment and Evaluation of Open-Angle Glaucoma: Ab Interno Canaloplasty Combined with In Vivotrypan Blue Ve-nography. ASCRS Virtual Annual Meeting 16-17 May, 2020. Riva I, Brusini P, Oddone F, et al. Canaloplasty in the Treatment of Open-Angle Glaucoma: A Review of Patient Selection and Outcomes. Adv Ther. 2019;36(1):31-43. Kodomskoi L, Kotliar K, Schroder AC, et al. Suture-Probe Canaloplasty as an Alternative to Canaloplasty Using the iTrack Microcatheter. J Glaucoma. 2019;28(9):811-817.