January 2019

GLAUCOMA

Presentation spotlight
Practical implantation and postop tips for the XEN implant


by Stefanie Petrou Binder, MD, EyeWorld Contributing Writer


A well-placed XEN implant
Source: Ahmed Elkarmouty, FRCS

XEN completely outside the AC in the subconjunctival space

OCT showing well-positioned XEN
Source: Ahmed Elkarmouty, FRCS

An expert discusses early experience with the gel stent

Innovative devices for use in microinvasive glaucoma surgery (MIGS) are proving to be highly effective in achieving sustainable IOP reductions in glaucoma patients maxed out on drops. The XEN Gel Stent (Allergan, Dublin, Ireland), approved in the U.S. since early 2017, has attracted attention due its relatively small surgical learning curve and its high potential to elicit marked changes in IOP due to its use of the untapped subconjunctival space. At the 2018 World Ophthalmology Congress, Ahmed Elkarmouty, FRCS, Moorfields Eye Hospital, London, U.K., reviewed the XEN implant so far and discussed his experience in 25 of his own patients.
Dr. Elkarmouty was an early adopter of the XEN. “The XEN implant redirects aqueous flow from the anterior chamber to the subconjunctival space,” he said. “It is the only ab interno MIGS approach that can create conjunctival drainage. The implant bypasses the trabecular meshwork and creates a new subconjunctival outflow pathway in individuals with primary open angle glaucoma who are not well managed on drops.”

Patient selection

Dr. Elkarmouty applies the XEN in patients eligible for trabeculectomy, showing a particular preference for this technology in certain patient groups, such as very young patients in whom he may want to cut down the fear factor and who have healthier conjunctiva; very old patients in whom XEN implantation is far less invasive with less intense aftercare; high myopes in which there is a high chance of hypotony following trabeculectomy and in whom trabeculectomy poses a risk of choroidals and macular folds; patients with a higher risk for developing uveitis; patients with a friable conjunctiva in whom conventional trabeculectomy or tube insertion may be difficult; glaucoma patients needing cataract surgery; patients with back pain who cannot have general anesthesia or tolerate lying supine for longer periods; and patients who have expressed the desire to be drop-free and choose a less invasive surgical option over trabeculectomy.
He conducted a study that included 25 patients (mean age 72 years; range: 39–95 years), of which 14 were Caucasian, nine were Black, and two were Asian. The patients each were on treatment regimens that included an average of three drops. Their mean IOP was 23±8 mm Hg, ranging from 14 mm Hg to 40 mm Hg.
The patients underwent XEN stent implantation under local anesthesia using a sub-Tenon’s block with lignocaine. Before implantation, Dr. Elkarmouty administered 0.1 mL of high dose anti-scarring agent in the subconjunctival space at 12 o’clock, which he spread across to the supra-nasal quadrant using spears.
The XEN implant is 6 mm in length with a 45 µm diameter. Insertion involves a preloaded disposable 27-gauge injector via a self sealing corneal incision. The surgeon crosses the anterior chamber to the upper nasal quadrant for implantation, creating a connection between the anterior chamber and the subconjunctival space via a scleral tunnel. XEN insertion does not come into contact with the iris or the corneal endothelium.

Outcomes

Dr. Elkarmouty presented his 6- and 12-month outcomes. The average IOP 1 year after the surgery was about 10 mm Hg, ranging from 5 mm Hg to 17 mm Hg. Following the IOP development over time showed that at 2 weeks, 25 patients had a mean IOP reduction of 9.4 mm Hg (95% CI 5.6–13.3, P=.0001). At 3 months, seven patients showed mean IOP reductions of 9.3 mm Hg (95% CI 5.8–12.7, P=.0006), and at 6 months, four patients showed mean IOP reductions of 9.8 mm Hg (95% CI0.8–18.7, P=.040).
He performed needling in five patients and in one patient who had undergone implantation combined with phaco. He noted a shallow anterior chamber in three patients postoperatively, which resolved on their own within a few days. Two patients underwent second XEN implantations, both of which were successful. No choroidals or maculopathy was observed in any of the study patients.
Dr. Elkarmouty is aggressive in his postoperative anti-inflammatory regimen. Patients receive triamcinolone via a sub-Tenon’s injection at the end of the procedure and get 0.1% dexamethasone every 2 hours for up to 3 months after the surgery, which he then tapers. He explained that the implementation of bleb needling is not driven by evidence of high IOP but by the healing response. “During the postoperative phase, we have a very low threshold for performing bleb needling,” he said. “We do not wait for an IOP spike to occur before performing this procedure. Any signs of an aggressive healing response such as early encapsulation or a fibrotic band causing bending of the subconjunctival portion of the XEN implant is considered an indication for bleb needling. This is carried out under topical anesthesia on a slit lamp using a 30-gauge needle and is followed by a subconjunctival injection of dexamethasone,” Dr. Elkarmouty said.
Complications of using the XEN can include subconjunctival or anterior chamber bleeding, XEN exposure in the anterior chamber in eyes in which the subconjunctival space is small, and the opposite situation in eyes in which the subconjunctival space is too large. Postoperative complications can include hypotony (physiological or numerical), scarring and failure, ischemic bleb, or XEN in the iris.

Corroboration

The FDA XEN investigation demonstrated at 12 months that 75% of patients achieved the target of greater than or equal to 20% IOP reduction from baseline on the same or fewer medications. The mean IOP decrease was 9 mm Hg, and the mean decrease in medications was 1.6. These eyes all underwent conjunctival dissection which, when omitted, could result in improved surgical outcomes.1
Another multicenter, international, interventional study that evaluated the XEN versus trabeculectomy revealed no significant difference in safety or efficacy between the two surgeries and showed 43% of the XEN eyes required needling.2
“Surgeons should keep in mind that needling may be required and need to be comfortable with this procedure when implanting the XEN microstent,” Dr. Elkarmouty said. “Also, be prepared to do your homework in terms of the aftercare for your patients. They require a careful follow-up. Revision may be necessary, however, a second stent implantation is a feasible option if the first stent fails.”

Surgical tips

Dr. Elkarmouty advised surgeons to plan the implant location before making their incision and to make sure the area is marked at 3 mm from the limbus. It is important to ensure that the Tenon’s is not adherent to the episclera and to prevent perforation by the needle when entering the subconjunctival space. He also marks an area where there are no conjunctival vessels to minimize risk of hemorrhage, which may obscure the needle entry into the subconjunctival space.
He explained that sleeve resistance could present a problem when entering the anterior chamber and to exercise caution in phakic eyes to avoid any damage to the lens. He uses pilocarpine drops before surgery in phakic eyes to minimize this risk.
When inserting the needle into the angle, he aims high and slightly anteriorly. Since viscoelastic deepens the anterior chamber considerably, it may interfere with the surgeon’s judgment of the angle anatomy, particularly if the procedure is not carried out under direct visualization by a gonioscopy lens. Finally, if injected too posteriorly in the angle, the XEN may enter the iris root or be too close to the iris, which may occlude its tip.
He advised surgeons to use traction while advancing the needle through the sclera until the full bevel can be seen and to remove traction and maintain a slight forward pressure with the injector while delivering the implant through gentle actuation of the slider.

References

1. Grover DS, et al. Performance and safety of a new ab interno gelatin stent in refractory glaucoma at 12 months. Am J Ophthalmol. 2017;183:25–36.
2. Schlenker MB, et al. Efficacy, safety, and risk factors for failure of standalone ab interno gelatin microstent implantation versus standalone trabeculectomy. Ophthalmology. 2017;124:1579–1588.

Editors’ note: Dr. Elkarmouty has no financial interests related to his comments.

Contact information

Elkarmouty
: ahmed.elkarmouty@moorfields.nhs.uk

Practical implantation and postop tips for the XEN implant Practical implantation and postop tips for the XEN implant
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