Ab Externo Canaloplasty

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Once 360 degree catheterization of the canal is complete, a suture is tied to the tip of the microcatheter before it is withdrawn, pulling the suture into the canal.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: Ab Externo Canaloplasty

  • 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.

Ab externo 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. Ab externo Canaloplasty is also suitable for the following:

  • 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

Ab Interno Canaloplasty, ABiC

Overview of the Procedure

  • Following cataract surgery, inject Miostat into the anterior chamber, followed by a dispersive viscoelastic. Create a sideport incision for inserting the iTrack™ microcatheter approximately 1 1/2 clock hours away from the 3-o’clock (right eye) or 9-o’clock (left eye) position. Next, insert the primed iTrack™ microcatheter into the anterior chamber.
  • Entering at the temporal location, create a small horizontal incision approximately 1-mm wide in the trabecular meshwork.
  • Using MST retina forceps, feed the iTrack™ microcatheter into Schlemm’s canal and align it flush to the trabecular meshwork. As the tip of the iTrack™ is advanced 360° to the initial incision site, follow its progress by observing the position of the red light.
  • Slowly withdraw the iTrack™ microcatheter while steadily injecting viscoelastic. Once this step is complete, remove all dispersive viscoelastic from the anterior chamber.
  • Unlike with traditional Canaloplasty, a tensioning suture is not placed into Schlemm’s canal during viscodilation.

Clinical Tips: ABiC

  • o Creating the Otomy: To create the otomy, I use a 27-gauge needle on a 3 mL syringe. I start high in the anterior of the trabecular meshwork and pull downward to approximately the middle of the trabecular meshwork, inserting the tip of the needle in the trabecular meshwork with the bevel facing toward the ceiling. When creating the otomy heme reflux can occur, and it may be necessary to refill the anterior chamber with OVD for better visualization. A whitish scleral color should help to identify Schlemm’s canal.

    Note: it is important that the otomy be situated central to the anterior of the trabecular meshwork. If the otomoy is too posterior in the trabecular meshwork, it will be impossible to stent because of the close proximity to the sclera.

  • It is recommended to use Miostat for all patients who undergo combined ABiC and phacoemulsification to avoid the angle’s narrowing after dilation.

Patient Selection: ABiC

ABiC™ is indicated for the reduction of elevated IOP in patients with open-angle glaucoma, including those with ocular surface disease and individuals who cannot tolerate anti-glaucoma medications. ABiC™ is also suitable for the following:

  • Pigmentary glaucoma (PG)
  • Pseudoexfoliation Glaucoma (PXF)
  • Ocular Hypertension
  • Post-SLT eyes
  • Eyes that have received a single session of low-powered ALT
  • Patients with previous failed trabeculectomy or tube surgery
  • OAG with narrow but not occludable angles after laser iridectomy
    (Note: Once a surgeon has gained the necessary experience, ABiC™ can also be performed on patients who have previously undergone trabeculectomy or tube surgery.)

ABiC™ is contraindicated for the following:

  • neovascular glaucoma
  • Multiple argon laser trabeculoplasty (ALT): Patients who have undergone more than one ALT procedure
  • Chronic uveitis
  • OAG with narrow angle (Note: unless canaloplasty and phacoemulsification are scheduled at the same time)
  • Narrow inlet with plateau iris