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Specialist gives pearls on gel stent implant
Xen combines the efficacy of subconjunctival filtration with a minimally invasive procedure.
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The Allergan Xen gel stent is a successful attempt to combine minimal invasiveness and maximum effectiveness, according to one specialist.
“It achieves mean IOP just 1 mm Hg above the pressure benchmark of trabeculectomy, combining the efficacy of subconjunctival filtration with a minimally invasive procedure,” Ingeborg Stalmans, MD, PhD, said.
With the plethora of surgical options available today, the hardest thing is to choose which treatment is the best for individual patients, and it seems difficult to find a balance between efficacy and safety, she said.
“With most MIGS you can achieve pressure in the mid to high teens, which might be OK in a proportion of our patients but is not low enough for patients with more advanced disease, when you are aiming for lower target pressures. Most of the procedures have been tested against phaco and show a minimal additional IOP lowering. They seem to be more suitable to lower the number of medications than to bring the pressure down convincingly,” she said.
On the other hand, trabeculectomy is effective and studies show consistent results with average pressure of about 12.5 mm Hg at 1 year, but complications are frequent.
APEX trial
The Xen is made of a permanent collagen-derived gelatin, is long with an inner diameter of 45 µm and is preloaded in an injector with a 27-gauge needle. It is injected through a small self-sealing corneal incision, travels through the anterior chamber, and goes through the trabecular meshwork, the sclera and then under the conjunctiva, creating a diffuse outflow from the anterior chamber to the subconjunctival space.
The device is currently under study in the prospective, multicenter, phase 4 APEX trial, enrolling a total of 215 eyes: 111 for Xen solo and 104 for Xen combined with cataract surgery. Mean preoperative IOP was 21.4 mm Hg, and patients were on an average of 2.5 medications.
One-year interim results showed that IOP dropped at day 1 just below 10 mm Hg, was maintained in the low teens, and after 12 months was 13.8 mm Hg with 0.6 medications. After 1 year, more than 55% of patients were off drops completely. Combination with phaco did not demonstrate any differences.
“We see that if the target pressure is below 18 mm Hg, you reach that target after 1 year in 93% of the patients. If it is below 16 mm Hg, it is still 82%, and if you aim at lower pressures, still 57% of patients reach target below 14 mm Hg and almost half below 13 mm Hg,” Stalmans said.
The only intraoperative adverse event above 1% was anterior chamber bleeding.
“Of course if you puncture the Schlemm’s canal, you can get some reflux. Not a big issue because you rinse it out together with the viscoelastic and then pressurize the eye a bit to prevent further bleeding,” she said.
Postoperative hypotony occurred in some patients but was asymptomatic and resolved within 1 week, with a well-formed anterior chamber, no loss of vision and no sign of maculopathy.
“Problematic hypotony is very rare with this procedure,” Stalmans said.
About 1% of patients had choroidal detachment, which resolved spontaneously within the first month. Only one patient needed an anterior chamber refill.
Stalmans said that Xen implantation is subconjunctival surgery and that there is a bleb, which can potentially develop fibrosis. The median needling rate in the study was 23.9%, which means an average of about 32%.
“In my view, it makes sense also for the Xen to use antimetabolites. I use MMC in all my Xen patients in a low 0.1 mg/mL concentration (100 µL), which is half of what I use in trabeculectomy. Use it posteriorly and don’t put it at the limbus — that’s the way to avoid avascular blebs,” she said. – by Michela Cimberle
- For more information:
- Ingeborg Stalmans, MD, PhD, is head of the Glaucoma Unit, University Hospitals Leuven (UZ Leuven), Belgium. She can be reached at Ophthalmology Department, University Hospitals Leuven, Herestraat 49, 3000 Leuven, Belgium; email: ingeborg.stalmans@mac.com.
Disclosure: Stalmans reports she is a consultant for Allergan and AqueSys.