Despite advancements in diagnostics and treatment, glaucoma continues to be the second-leading cause of blindness worldwide.1 It is estimated that currently over 80 million people, globally, have glaucoma, with over 4.22 million of those residing in the United States.2,3 This number is destined to rise as the population ages.
More and more eyecare providers are taking an interventional approach to directly address the underlying causes of the disease instead of solely focusing on medical management. Minimally invasive glaucoma surgery (MIGS) is one of the ophthalmologist's most effective tools.
XEN: Background and basics
Among the most versatile options is the XEN Gel Stent (Allergan), a MIGS device designed to lower intraocular pressure (IOP) in patients with open-angle glaucoma (OAG) by creating a subconjunctival filtration pathway.4
Unlike other MIGS that target Schlemm’s canal or the supraciliary space, the XEN stent was the first device to utilize a micro-incisional ab interno technique to shunt aqueous humor from the anterior chamber directly into the subconjunctival space. The device relies on the Hagen-Poiseuille law to maintain controlled aqueous outflow.5
Clinical studies have demonstrated that the XEN Gel Stent can reduce IOP by up to 56% and decrease the need for topical medications by as much as 2.7 agents at 12 months post-implantation, with fewer complications compared to traditional trabeculectomy.6
Ab interno vs. ab externo technique with the XEN Gel Stent
Although traditionally performed using an ab interno technique requiring a corneal incision and intra-operative gonioscopy, the XEN procedure has evolved to include an ab externo approach.4
This newer method allows for greater surgical control, including:
- Direct conjunctival manipulation
- Precise stent placement
- Application of adjunctive agents, such as mitomycin C, to modulate wound healing
The ab externo technique eliminates the need for corneal incisions and allows for revision or stent repositioning if necessary.3 Additionally, the incidence of post-operative bleb needling appears to be reduced compared to the ab interno method. These advancements underscore the adaptability of the XEN Gel Stent and highlight its growing role in the surgical management of refractory OAG.1
What are your patient selection criteria for XEN?
There is a broad selection criteria for XEN. I use it in open-angle glaucoma patients who are either uncontrolled with their current drop regimen or who are intolerant/noncompliant to their current drug regimen. I avoid it in eyes that are inflamed from uveitis, neovascular issues, or previous multiple surgeries.
Do you prefer the ab externo or ab interno approach?
I prefer an ab externo approach, because I am able to dissect a clear plane under the Tenon's capsule, so there is a clear path of aqueous through the XEN.
I can also identify exactly where and how many millimeters of the XEN Gel Stent are placed behind the limbus, ensuring proper placement. Overall, I find there is more control with the ab externo approach. If I am combining XEN with cataract surgery and don't want to open the conjunctiva, I opt for the ab interno XEN technique.
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Surgical Videos of Ab Externo XEN Gel Stent Placement
Watch the narrated surgical videos of two ab externo approaches to XEN Gel Stent placement, with pearls from Dr. Bedrood.
What factors influence your choice between open and closed ab externo XEN placement?
If the patient has a mobile conjunctiva and I have a good ability to dissect the plane underneath Tenon’s and close the conjunctiva, then I prefer doing an open ab externo XEN placement. If I suspect they have a lot of Tenon’s tissue, then I prefer to open and create a clean plane under the tenon’s capsule.
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Surgical Videos of Ab Externo XEN Gel Stent Placement
Watch the narrated surgical videos of two ab externo approaches to XEN Gel Stent placement, with pearls from Dr. Bedrood.
5 surgical pearls for ab externo XEN surgery
- Create a 1 to 2 clock hour peritomy and dissect underneath the Tenon's tissue as cleanly as you can without disrupting blood vessels, while using cautery to control bleeding.
- Mark the eye 2.5mm behind the limbus as a guide to the most posterior point. The injector should be inserted behind the limbus.
- Once the XEN is injected, wait and make sure there is fluid coming from the stent, not just from around the XEN. Note that the higher the IOP, the more quickly the aqueous comes out.
- Sometimes I induce pressure by pressing on the globe to make certain there is fluid and to ensure the other end is not entrapped in the iris or clogged in some other way.
- Once you close, make sure the stent is easily mobile underneath the conjunctiva. I usually use the end of a cannula to try to move the stent from side to side once the conjunctiva is closed.
- If there is not, consider primary needling to move the Tenon’s capsule out of the pathway of the XEN opening.
- Post-operative care of the bleb is essential for success; I give prednisolone every 2 hours for the first month then do a gradual taper.
In conclusion
The XEN Gel Stent represents a significant advancement in the surgical management of open-angle glaucoma, offering a minimally invasive alternative to traditional filtration procedures with a favorable safety profile. Its ability to effectively reduce IOP while minimizing tissue disruption makes it an appealing option for both patients and surgeons.
Careful patient selection and the ability to identify which implantation method should be utilized are both essential to optimizing success and minimizing complications. However, as ophthalmologists seek to balance efficacy with safety, the XEN procedure continues to stand out as a worthwhile weapon in the modern glaucoma treatment armamentarium.
