Canaloplasty is a highly effective surgical technique for the treatment of open-angle glaucoma. Minimally invasive, it restores the function of the eye’s natural outflow system without the need for a filtering bleb – offering an unprecedented level of efficacy and safety in the surgical treatment of glaucoma. With over 60,000 procedures performed to date, clinical studies have shown that Canaloplasty provides an improved safety profile with infrequent intra-operative and post-operative complications and does not result in bleb-related issues compared to traditional glaucoma surgery, such as trabeculectomy. As an added benefit, Canaloplasty does not preclude or affect the outcome of future surgical intervention.
Restoring the Outflow Pathways
Canaloplasty works by restoring the natural outflow pathways,. During the procedure, 360-degree viscodilation of Schlemm’s canal acts as a form of angioplasty and opens up the ostia of the collector channels, re-establishing outflow. Specifically, the precisely controlled delivery of Healon/Healon GV during withdrawal of the iTrack™ microcatheter separates the compressed tissue planes of the trabecular meshwork, and also triggers the withdrawal of any herniated inner wall tissue from the collector channels.
Sites of Resistance?
One of the challenges of glaucoma treatment is that the location of increased aqueous outflow resistance and how this resistance is generated is unclear. If a glaucoma surgeon were to remove the site(s) where increased outflow resistance resides, IOP would fall. However, if it is not possible to identify the site(s) of increased outflow resistance in a specific POAG eye, it is difficult to determine which parts of the outflow system are more relevant than others in terms of lowering IOP. Consequently, it is important to address all aspects of the ocular outflow system.
The Importance of the Collector Channels
Canaloplasty is the only glaucoma surgery that addresses blockages in the collector channels.
In a healthy eye, aqueous humor drains from the anterior chamber through progressively smaller channels of the trabecular meshwork into the circumferentially-oriented Schlemm’s canal. From Schlemm’s canal, circuitous channels, known as the collector channels, wind their way toward the surface of the sclera through the intrascleral venous plexus system, joining the episcleral vasculature, which drains into the venous system. It is important to note that the collector channels are not evenly distributed around Schlemm’s canal circumferentially and that outflow is segmental, higher in areas close to the large collector channels.
Studies undertaken in human POAG eyes by Haiyan Gong, MD, PhD (University of Boston) have shown that many of the collector channels may be blocked with herniated trabecular meshwork tissue at 0mmHg and become progressively worse as IOP rises1. This herniated tissue does not recede in POAG eyes although it does in normal eyes. Cannulating the whole of Schlemm’s canal with Canaloplasty, via a process of 360-degree visco-dilation, may “pop” open these herniations and enable full access to collector channel ostia for the egressing aqueous. In the case of other glaucoma treatments, where only a segment of Schlemm’s canal is addressed, or where the trabecular meshwork is targeted in isolation, any herniated tissue would most likely prevent improved outflow.
Research Summary: Haiyan Gong
In POAG eyes fixed at 0 mmHg (N=5), 73 collector channel ostia regions were examined, with 51 showing herniations (70%). In POAG eyes fixed at 10 mmHg (N=2), 22 collector channel ostia regions were examined, with 21 showing herniations (95%). In contrast, in normal eyes fixed at 0 mmHg, 53 collector channel ostia regions were examined, with 8 herniations found (15%). Whilst these herniations were found to be reversible in normal eyes, they were irreversible in the POAG eyes.
- Source: Cha ED, Xu J, Gong H. Variations in active areas of aqueous humor outflow through the trabecular outflow pathway. Presented at ARVO 2015.
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