Norbert Körber, MD

The current gold standard in glaucoma surgery is undoubtedly trabeculectomy but it is not without its risks. Complications are sometimes immediately noticeable; occurring during surgery, or only becoming evident years after the original procedure was conducted. It is not uncommon to see suprachoroidal haemorrhage, choroidal effusion, cataract formation, bleb leaks and bleb infections/endophthalmitis. Consequently, surgeons are always on the look out for new methods and techniques that will evolve glaucoma surgery to even higher levels, offering patients safer and more effective treatment options.

The idea of non-penetrating surgery to lower intraocular pressure (IOP) has increased in popularity and today several such methods are used. For example, I stopped performing trabeculectomies in 1997 and began using the viscocanalostomy technique instead, which is far less invasive. However, this also has its drawbacks; such as not being able to open Schlemm's canal throughout the complete circumference of the anatomy. Additionally, the risk of failure associated with this procedure stems from the possible closure of the ostia of Schlemm's canal during the healing process postoperatively.

Why choose canaloplsty?

Figure 1: Cannulation of Schlemms Canal with ophthalmic microcatheter.

In my quest to achieve improved results and lower rates of complications, I started exploring canaloplasty. Canaloplasty represents a new advance in non-penetrating glaucoma surgery that is designed to revitalize the natural outflow system of the eye, resulting in a sustained reduction of IOP. The outcome is an improvement in the aqueous circulation through the trabeculocanalicular outflow process. It is my experience that canaloplasty can offer a number of advantages over other techniques, such as trabeculectomy, by enhancing aqueous outflow without creating a bleb.

Figure 2: iTrack ophthalmic microcatheter with illuminated beacon tip.

Canaloplasty is a 360 degree viscodilation of the Schlemm's canal (Figure 1) with a microcatheter which has an illuminated tip (Figure 2). The new microcatheter, called the iTrack (iScience Interventional), enables sustained dilatation of the Schlemm's canal throughout its complete circumference. The iTrack can be used to insufflate Schlemm's canal with viscoelastic as part of an enhanced viscocanalostomy technique and as a guide for placing an intracanalicular suture to distend the trabecular meshwork inwards, thus permanently opening Schlemm's canal. Instead of just dilating 120 degrees of the canal it is now possible to inject viscoelastic, in an atraumatic manner, throughout the entire 360 degrees of the canal.

The iTrack has a diameter of 200 μm and an atraumatic soft tip. A helium-neon light source called the iLumin provides a visible reference point for the microcatheter tip during canaloplasty. This beacon tip provides direct visualization of the microcatheter location within Schlemm's canal, enhancing surgeon control and the microcatheter tip contains a lumen for the injection of viscoelastic.

In conjunction with the microcatheter and illumination system, a new high-resolution ultrasound system provides accurate localization of Schlemm's canal and can also provide confirmation of the outcome of canaloplasty.

Step-by-step

• To perform canaloplasty, I begin with a limbal opening of the conjunctiva, followed by a 4.5 x 4.5 mm parabolic scleral flap of 300 μm thickness, advanced 1 mm into clear cornea.
• A second flap, 0.5 mm smaller, is dissected down to the last existing layers of the sclera, thus easily revealing Schlemm's canal when advancing to the limbal area.
• After exposing the trabecular meshwork, the flap is gently advanced into the cornea, exposing Descemet`s membrane around 0.5 to 0.7 mm from Schwalbe's line.
• Both ostia of Schlemm's canal are then dilated with a microcannula and the iTrack catheter is advanced in small steps into the complete circumference of the canal, injecting minuscule amounts of high viscosity viscoelastic every two clock-hours to dilate the canal to a width of approximately 300 μm.
• Prior to retracting the iTrack, a 10-0 polypropylene suture is attached to the tip of the catheter, pulled through the canal and tied at a certain tension force to apply a permanent traction on the trabecular meshwork from within. This effect can be accurately monitored with the high-resolution ultrasound system, showing the change of shape at the trabecular meshwork by the suture. The pressure effect of the whole process is strongly dependent on the suture tension, as we discovered during the study.