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BLOG: We have the Xen gel stent — the Triforce is now complete
This holiday season may be one of the best ever for glaucoma patients and the doctors who care for them. The FDA approval of the Xen gel stent from Allergan now completes the Triforce for microinvasive glaucoma surgery. For those of you who are gamers and familiar with the Legend of Zelda series, you will naturally understand the importance of this occasion. If you are not one of those people, then let me explain.
MIGS can be divided into three major anatomical targets: trabecular bypass/Schlemm’s canal, suprachoroidal/supraciliary, and subconjunctival space. These sites represent possible routes to direct aqueous from the anterior chamber in order to decrease IOP. In the ideal work environment, surgeons would be able to use all three targets. The ability to use each of these sites is important, but the best benefit could come from a synergy of them possibly put together. The iStent (Glaukos) was the first piece of the puzzle when the FDA approved its use in 2012. It allows surgeons to safely re-establish aqueous flow through diseased trabecular meshwork to recreate natural physiologic flow. This situation remained fixed for a few years until just a few months ago when the CyPass (Alcon) gained approval. The CyPass leads aqueous from the anterior chamber to the supraciliary and then suprachoroidal space. The second piece of the puzzle came into place. It just so happens that several weeks after that event, the third and final component was approved with the Xen gel stent. The Xen stent permits aqueous to move from the anterior chamber to the subconjunctival space similar to that of gold standard trabeculectomy surgery.
For the newest stent on the block, the Xen, there are distinct advantages that allow for good pressure almost like a trabeculectomy but without acting like one when it comes to risks:
1. The 6 mm length along with the 45 µm inner lumen creates a 6 mm Hg to 8 mm Hg resistance gradient to help prevent hypotony.
2. The unique composition of the stent, which is a porcine gelatin with glutaraldehyde, hydrates when it comes into contact with aqueous, allowing it to swell and form a tight seal in the passage created through the sclera, further protecting from hypotony.
3. The stent is placed ab interno without the need to make any incisions on the conjunctival tissue, which eliminates secondary issues stemming from wound leaks and preserves the conjunctival tissue should a trabeculectomy be needed later.
4. The Xen bleb that is created, which helps achieve its pressure reduction and long-term success, is much improved compared with its trabeculectomy counterpart as it is easier to create and maintain.
What a truly exciting time it is for all. The three-legged puzzle of MIGS is finally complete (aka, Link has gained the Triforce). Now armed with these procedures, we can move on to the next stage in our quest, which is better taking care of our glaucoma patients. Maybe we can even save Princess Zelda and restore the Kingdom of Hyrule along the way!
Disclosure: Teymoorian reports he is a consultant for Alcon, Allergan and Glaukos.