Efficacy of Gel Microstent for Primary Open-Angle Glaucoma

XEN Glaucoma Implant With Mitomycin C 1-Year Follow-up: Result and Complications

Galal A, Bilgic A, Eltanamly R, Osman A
J Ophthalmol. 2017;2017:5457246

Study Summary

Galal and colleagues performed a prospective interventional study in 13 eyes of 10 patients with primary open-angle glaucoma to evaluate a gel microstent (XEN®; AqueSys, Inc).

Inclusion criteria required that patients had uncontrolled intraocular pressure (IOP), were intolerant to therapy, or were on maximal therapy but undergoing cataract extraction. XEN implantation was performed by one surgeon, and all patients were treated with subconjunctival mitomycin C. Of the 13 eyes, three were pseudophakic and 10 underwent simultaneous phacoemulsification.

Patients were followed for 1 year after surgery, with evaluation of IOP, number of medications, vision, and complications.

IOP reduction ≥ 20% from preoperative baseline at 1 year without any glaucoma medications was defined as complete success; partial success was defined as IOP reduction of ≥ 20% at 1 year with medications. Complete success was achieved in 42% of eyes and 66% qualified success. After 1 year, IOP decreased from 16 ± 4 mm Hg at baseline to 12 ± 3 mm Hg. The number of medications decreased from a mean of 1.9 ± 1 at baseline to 0.3 ± 0.49.

Complications included implant extrusion in one eye and choroidal detachment in two eyes, and two eyes required trabeculectomy.

Viewpoint

The XEN implant, made from cross-linked porcine collagen, aims to provide a conduit for aqueous to flow from the anterior chamber to the subconjunctival space, similar to trabeculectomy. With its lumen diameter of 45 µ and length of 6 mm, the XEN 45 implant used in this study provides aqueous filtration of around 2-2.5 mL/min.

Unlike in trabeculectomy, the approach to the angle is ab interno.^[1] The device is implanted through the scleral spur and tracked 3 mm posterior to the limbus, with exit through the sclera into the subconjunctival space. About 2 mm of the implant remains in the anterior chamber to allow connection to the subconjunctival space.

The benefit of this procedure over the gold standard trabeculectomy mostly derives from the fact that the conjunctiva does not need to be manipulated externally for this procedure. This potentially reduces the risk for leaks, scarring, and failure. Also, the ab interno approach shortens the surgical time because the conjunctiva and sclera do not require suturing.

But, as the authors mention, it is debatable whether the XEN implant should be included in the category of minimally invasive glaucoma surgery (MIGS), because the conjunctival space is still used for passage of aqueous as opposed to increasing flow through the trabecular meshwork or the supraciliary space, as with some other MIGS devices.

That is an important consideration, because clinicians need to be properly prepared should the patient need another surgery after the XEN implant. If the conjunctiva is scarred, standard trabeculectomy may be more difficult or impossible.

In this study, two patients needed further intervention with standard trabeculectomy to reduce intraocular pressure. Given the small sample size, the need for further surgical intervention in this study was > 15%. Although the authors report a complete success rate of 42% and a qualified success of 66%, these rates are considerably lower than that with trabeculectomy, which has been reported to have qualified success of almost 90%.^[2]

The amount of IOP decrease is also less with the XEN implant compared with trabeculectomy or tube implants.^[3] Yet, the conjunctiva is relatively spared; surgical time is shorter; and there is decreased risk for vision-threatening complications, such as suprachoroidal hemorrhage, persistent hypotony, or flat anterior chamber. In this study, no such complications were reported, although two patients had choroidal effusions and one eye had implant extrusion.

Therefore, the overall success rates and absolute reduction in pressure is less than that of trabeculectomy or tubes. The risk for transient choroidal effusions and hypotony is similar to that with trabeculectomy and tube procedures (19% and 16%, respectively, per the Tube Versus Trabeculectomy trial^[3]), but the risk for more vision-threatening complications is significantly less.

This device can be implanted in conjunction with cataract surgery or as a stand-alone procedure. Surgeons who are familiar with angle anatomy and comfortable manipulating a gonioscopy lens will probably find this procedure easy to perform, with a steep learning curve. Choosing a good candidate for the procedure is key to reducing intraoperative complications; therefore, gonioscopic exam at the slit lamp should be performed on all potential patients before surgery. In patients in whom there is good visualization of the angle and a need for moderate pressure reduction, this implant may be a good choice.

Further data with larger sample sizes as well as more long-term data are needed before it can be determined where the XEN implant falls among emerging devices and procedures for IOP reduction.

Abstract

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