iTrack microcatheter system offers efficacy, versatility in glaucoma surgical space
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In the past decade, scientific and imaging techniques have allowed us to understand the eye’s physiologic aqueous outflow system to an unparalleled degree.
Aqueous flows from the anterior chamber and traverses trabecular lamellae leading into the juxtacanalicular space and Schlemm’s canal. From there, aqueous flows segmentally into the collector channel system and moves through aqueous veins that lead into episcleral veins to join the systemic vasculature.
Along this aqueous journey, there are multiple potential points for outflow resistance leading to increased IOP and associated glaucomatous optic neuropathy. These resistance points include the juxtacanalicular trabecular meshwork, the inner wall of Schlemm’s canal and, more distally, the collector channel ostia. Glaucoma surgical intervention with the iTrack microcatheter (Nova Eye Medical) allows one to address all of these resistance points to various degrees based on risk-benefit tolerance for an individual patient.
The iTrack microcatheter consists of a 250 µm shaft enclosing a guidewire as well as a fiber optic illuminating tip. The illuminating tip allows one to visualize entry and passage into Schlemm’s canal for up to 360° (Figure 1).
Source: Ahmad A. Aref, MD, MBA
Gonioscopy-assisted transluminal trabeculotomy
Gonioscopy-assisted transluminal trabeculotomy (GATT) involves disruption of the juxtacanalicular trabecular meshwork and inner wall of Schlemm’s canal to address these areas of aqueous outflow resistance. After a nasal corneal paracentesis incision, a temporal clear corneal incision and limited goniotomy, the iTrack catheter may be threaded, ab interno, into Schlemm’s canal for up to 360°. The surgeon may then apply tension to each end of the catheter in order to “break through” the inner wall of Schlemm’s canal and trabecular meshwork in order to address these two resistance points to aqueous outflow. Several studies have supported the efficacy of this procedure in various stages of glaucomatous disease. In one retrospective report of 198 adults, patients experienced an IOP decrease of 9.2 mm Hg along with an average decrease of 1.43 glaucoma medications after 24 months of follow-up. This corresponded to an average IOP reduction of 37.3% from baseline.
Ab interno canaloplasty
The ability to infuse viscoelastic across the tip of the iTrack microcatheter allows the surgeon to address distal resistance points to aqueous outflow, namely areas of Schlemm’s canal collapse and also the collector channel ostia. To accomplish this, the surgeon creates a nasal corneal paracentesis incision, a temporal clear corneal wound and limited goniotomy. The iTrack catheter is fed into Schlemm’s canal through the goniotomy site for up to 360° ab interno. The surgeon may visualize the illuminated microcatheter tip throughout the process in order to ensure proper positioning. After threading, rather than applying tension to the two catheter ends, the surgeon slowly withdraws the external catheter segment such that the device “backs out” of the canal the way it originally passed. During the process, the surgical assistant injects viscoelastic through the catheter tip in order to dilate and distend Schlemm’s canal and collector channel orifices. In a retrospective case series of 60 eyes treated with ab interno canaloplasty (ABIC) with or without phacoemulsification surgery, the procedure reduced IOP from a baseline of 20 ± 4.9 mm Hg to 13.5 ± 2.6 mm Hg (P < .001). Importantly, results did not differ when ABIC was performed in conjunction with cataract surgery vs. as a stand-alone procedure.
Combined GATT and ABIC surgery
Combining GATT and ABIC in one surgical setting allows the surgeon to address multiple points of aqueous outflow resistance for up to 360°. Once the ABIC portion of the procedure is performed, the iTrack catheter may be rethreaded into Schlemm’s canal for up to 360° before performing GATT. In a prospective case series of 20 eyes with primary open-angle glaucoma, combined GATT, ABIC and cataract surgery reduced IOP from a mean baseline of 19.75 ± 4.68 mm Hg to 13.3 ± 1.3 mm Hg at 12 months, corresponding to a percentage reduction of 32.7%.
Surgical success
Intraoperatively, one marker for successful treatment of aqueous outflow resistance is the episcleral venous fluid wave. Once GATT and/or ABIC has been performed, the surgeon may inflate the anterior chamber with balanced salt solution and potentially observe fluid flow through the collector channel system, aqueous veins and episcleral veins. Observation of this vascular fluid wave or blanching (Figure 2) signifies successful bypass of resistant sites to aqueous outflow.
Versatility and personalization of care
GATT and ABIC may be performed together or separately and as stand-alone procedures or in combination with cataract surgery. Furthermore, the procedures may each be performed for a full 360° or to a lesser extent. These multiple surgical levers allow one to modify the risk of the procedure according to the desired benefit for an individual with a given disease stage who may or may not have a visually significant cataract. As an ab interno procedure, the conjunctiva is spared for future glaucoma filtering procedures if required.
- References:
- Al Habash A, et al. Clin Ophthalmol. 2020;doi:10.2147/OPTH.S267303.
- Fellman RL, et al. J Glaucoma. 2019;doi:10.1097/IJG.0000000000001126.
- Gallardo MJ. Clin Ophthalmol. 2021;doi:10.2147/OPTH.S272506.
- Grover DS, et al. J Glaucoma. 2018;doi:10.1097/IJG.0000000000000956.
- For more information:
- Ahmad A. Aref, MD, MBA, can be reached at Illinois Eye & Ear Infirmary, University of Illinois at Chicago College of Medicine, 1855 W. Taylor St., Chicago, IL 60612; email: aaref@uic.edu.
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