Overview of the Ab-Externo Canaloplasty Procedure

During the procedure, the trabecular meshwork plates are stretched by a suture, which is tied and left in situ in Schlemm’s canal, also ensuring that the canal stays open. The canal itself is dilated over 360 degrees to more than 250 microns in diameter, which helps to pop open any previously obstructed collector channel ostia and restore the natural outflow pathways.

Overview of the Procedure
  • A superficial hinged flap of sclera is created, followed by a deep flap that advances anteriorly to expose Schlemm’s Canal and to create the Descemet’s Window.
  • The iTrack™ microcatheter is introduced into the canal and advanced around its entire circumference.
  • Once 360 degree catheterization of the canal is complete, a suture is tied to the tip of the microcatheter before it is withdrawn, pulling the suture into the canal. At the same time, viscoelastic is delivered through the microcatheter to widen the canal, and to open the adjacent collector channels. This process restores the natural outflow pathway of the aqueous humor to the aqueous veins.
  • The suture is cut from the microcatheter and tied in a loop encircling the inner wall of the canal. The suture is then tightened to distend the trabecular meshwork with the aim of widening the trabecular spaces.
  • The superficial flap is sutured tightly over the space left by the excised flap, which results in the creation of a scleral lake. If needed, percolation through Descemet’s Window can be improved post-surgery with a YAG laser.

Clinical Tips: Canaloplasty

 Clinical Tips
Size of Incision: Make your incision large, i.e., 5×5 mm for a good exposure until you gain familiarity with the procedure.
Anatomical Landmarks: Use high magnification on your microscope during cut-down of the deep flap in order to recognize the surgical anatomical landmarks, such as the scleral spur.
Schlemm’s Canal: Good exposure of the Schlemm’s canal ostia is crucial. Schwalbe’s Line Detachment: Once Schlemm’s canal is exposed use only a blunt instrument (spatula) or Weck-cell sponge to detach Schwalbe’s Line (SL). Sudden egress of aqueous humor may be observed during the proper detachment.
Creation of Descemet’s Window: After lowering IOP via paracentesis, dissect the sides with gentle upward strokes while holding the bottom of the deep flap with your forceps on the same side as where you are applying the upward strokes.
Trabeculo-Descemetic Window: Check the flow through the Trabeculo-Descemetic Window and follow the 3-second rule – add balanced salt solution (BSS) to the anterior chamber to bring the IOP to the high teens; dry the scleral bed. Within three seconds the whole bed should be filled with aqueous humor.
Perforation of Descemet’s Window: Perforations may occur, but can easily be addressed while continuing with Canaloplasty. There is no need to convert to Trabeculectomy. Opening of Schlemm’s Canal Ostia: Use a Grieshaber or 30 gauge introducer cannula by placing it on top of the trabecular meshwork, parallel with the scleral spur, coaxial to Schlemm’s Canal ostium.
Catheterization: Activate the lubricious coating by dipping the working length of the microcatheter into BSS. Prime the catheter with Healon and insert into an ostium while Healon is still oozing from the tip of catheter. This will be enough for gentle, atraumatic catheterization. Full Circumferential Catheterization: Generally speaking, the iTrack™ microcatheter passes through 360 degrees very readily; however, it may become stuck at times, most commonly in the ostium of a super collector channel. The easiest way to address an obstruction is to remove the iTrack™ and re-enter counter-clockwise.
Suture Tension: Use a slipknot to control and adjust the tension. Tighten until you see dimpling or folds in the trabecular meshwork. Ensure watertight closure to restore natural physiological outflow without creating a filtering bleb.
End of the Surgery: Refill the Anterior Chamber with BSS and bring IOP to at least 20mmHg; by doing so there will be less hyphema at day 1 as the flow of aqueous will be forced out through the newly opened Collector Channels.
Post-Operative Regimen: Take the patient off anti-glaucoma medication and follow standard post-cataract regimen with antibiotics and anti-inflammatory therapy.

Patient Selection: Canaloplasty

Canaloplasty is indicated for the reduction of elevated IOP in open-angle glaucoma (OAG) patients, including OAG with ocular surface disease and patients intolerant to anti-glaucoma medications. Canaloplasty is also suitable for the following:

Patient Selection
  • Pigmentary Glaucoma (PG)
  • Pseudoexfoliation Glaucoma (PXF)
  • Ocular Hypertension
  • Normal Tension Glaucoma (NTG)
  • Juvenile Glaucoma
  • Steroid Induced Glaucoma
  • Patients Post-SLT
  • Patients Post single session low power ALT
  • Patients with previous failed trabeculectomy or tube surgery (Note: Once a surgeon has gained the necessary experience, Canaloplasty can also be performed on patients who have previously undergone trabeculectomy or tube surgery.)
Canaloplasty is contraindicated for the following:
  • Neovascular Glaucoma
  • Multiple Argon Laser Trabeculoplasty (ALT): Patients who have undergone more than one ALT procedure
  • Chronic Uveitis
  • Peripheral Anterior Synechiae
  • Patients with a History of Angle Closure
  • OAG with narrow but not occludable angles after laser iridectomy (Note: Canaloplasty without a suture could be considered)
  • OAG with narrow angle (Note: unless Canaloplasty and Phacoemulsification are scheduled at the same time)
  • Narrow inlet with plateau iris
  • Angle Recession Glaucoma