July 2019

IN FOCUS

MIGS Update
The XEN 45 ab externo


by Chiles Aedam R. Samaniego EyeWorld Contributing Writer


In the open conjunctival
approach, a peritomy is open and the XEN gel stent is inserted via an ab externo approach.


With an open conjunctival
peritomy, the XEN gel stent
position can be easily adjusted after it is injected to ensure proper positioning.


Once the XEN gel stent is placed in the desired position, it is safely tucked under the conjunctiva and the conjunctival peritomy is closed.
Source: Joseph Panarelli, MD

At a glance

• As use of the XEN 45 evolves, surgeons are embracing an ab externo approach to implanting the device, though exact techniques vary.
• While some surgeons have almost completely shifted to using an ab externo approach for the XEN 45, it may still be advisable for them to learn ab interno
implantation techniques first before exploring ab externo techniques, for which there is currently no manufacturer protocol.
• In addition to the XEN 45, the PreserFlo—formerly the InnFocus Microshunt—is expected to significantly impact glaucoma surgical practice, though head-to-head comparison of the two devices is yet to be made.

New techniques to implant the XEN 45 gel stent (Allergan) have evolved as surgeons try to find ways to optimize the efficacy and safety of the implant as well as the ease of implantation, said Anna Do, MD, and Joseph Panarelli, MD, in correspondence.
At their practice, they have used various approaches to implant the stent: ab interno into the subconjunctival space (closed approach), ab interno beneath the Tenon’s layer (open approach), and ab externo beneath the Tenon’s layer (open approach) while using variable doses of mitomycin-C (MMC).
The ab interno approach is the traditional method for implanting the XEN stent, an FDA-approved microinvasive surgical device for medically refractory open angle glaucoma (mrOAG). Recently, however, surgeons have begun embracing the ab externo approach to make an already minimally invasive procedure even less invasive.
EyeWorld consulted Dr. Do and Dr. Panarelli as well as experts Davinder Grover, MD, and Won Kim, MD, regarding this new approach.

Evolving practice patterns

Dr. Kim has extensive experience with the device, beginning about 2 years ago using the traditional ab interno technique. “Overall, this worked well but the needling rate was 50%,” he wrote.
He then tried the “air XEN” technique championed by Iqbal “Ike” Ahmed, MD, which separates the conjunctiva from the underlying Tenon’s through pneumodissection to create a supra-Tenon’s pocket for the XEN implant. “This is then followed by typical ab interno XEN implantation,” he said.
Air XEN cut Dr. Kim’s needling rate in half but added complexity to the surgery.
“In October 2018, I had the thought of trying to implant the XEN stent ab externo without any incisions directly through the conjunctiva in a technique similar to bleb needling,” Dr. Kim said. “I was unaware at the time that Sebastien Gagne had been doing this since 2016 in Canada. I was also unaware that there were several other surgeons in the U.S. who started doing this around the same time.”
Among those surgeons who started using this approach in October 2018 was Dr. Grover. Dr. Grover had been involved in the initial FDA pivotal trial so had plenty of experience using the ab interno technique before incorporating the ab externo technique.
The ab externo approach, Dr. Grover said, is an even less invasive way of doing the surgery. “You don’t actually need to make an incision in the cornea at all. It is a very streamlined method, so it’s an efficient way of performing the surgery,” he said.
“This approach was a revelation,” Dr. Kim said. “Its speed, simplicity, and effectiveness at avoiding Tenon’s entanglement was a significant advantage over ab interno approaches. The visual recovery was almost instantaneous as the surgery did not require any incisions into the cornea or the conjunctiva. This incision-less ab externo transconjunctival approach has been dubbed the ‘XEN-ex’ technique.”
Like air XEN, XEN-ex “dramatically lowered” Dr. Kim’s needling rates compared to ab interno XEN implantation; unlike air XEN it is much easier to perform and teach to residents. “The simplicity of this approach is key,” he said.

Variations

The parallel evolution of the ab externo approach among surgeons has led to variations in the exact technique individual surgeons use.
At their practice, Dr. Do and Dr. Panarelli prefer first injecting MMC at 60–80 mcg 10 mm posterior to the limbus, then making a 3–4 clock hour peritomy. “The XEN is then inserted via an ab externo approach into the anterior chamber and the peritomy is closed with the stent safely tucked beneath the Tenon’s layer,” they said. “Performing a limited tenonectomy may decrease the risk of stent obstruction/early failure; however, this may potentially lead to a higher risk of erosion through the conjunctiva.”
Meanwhile, though Dr. Kim uses XEN-ex in the majority of his cases, he said: “For cases at high risk for failure (young, deeply pigmented, inflamed conjunctiva patients), I will do ‘open XEN’ cases utilizing a fornix-based conjunctival peritomy combined with a generous tenonectomy and ab externo XEN implantation.” Dr. Kim weighs the advantages against disadvantages such as the risk of erosion in each patient. In addition, to minimize the risk with the open XEN tenonectomy technique, he sutures the XEN to the sclera with a 9-0 vicryl suture to make it flat.
Dr. Grover, on the other hand, doesn’t make a peritomy at all. “I usually tent the [conjunctiva] over and move the conjunctiva and drag it into place so that the buttonhole through the conjunctiva is nowhere near where the XEN will actually be; this minimizes the risk of erosion and exposure,” he said. “Some people tunnel through the subconjunctival space; I pinch the conjunctiva and move it into place.”
One trick Dr. Grover does, which he credits to Oluwatosin Smith, MD, is putting ink on the tip of the XEN implant injector needle to allow him to know exactly where his conjunctival insertion site is located, whether it is Seidel positive and to confirm it is well away from the XEN implant.
Performing under topical anesthesia, Dr. Grover uses a traction suture to control the eye and uses preservative-free dexamethasone on a 30-gauge needle to reform the eye. Rather than making a paracentesis, he will insert the 30-gauge needle through the cornea and inject this solution into the anterior chamber any time he needs to pressurize the eye. This modification again streamlines the surgery and avoids using a 15-degree blade and a viscoelastic.
He also uses MMC after injecting the implant through a sub-Tenon’s injection.

In/ex

“Extremely fast, extremely simple, and intuitive,” Dr. Kim said that the ab externo approach requires no incisions in the cornea, no viscoelastic, no balanced salt solution irrigation, and can be performed through a usually self-sealing 27-gauge needle tract in the conjunctiva and allows almost immediate visual recovery. The approach also allows superotemporal implantation and avoids entanglement in Tenon’s capsule, a major cause of XEN failure.
Dr. Grover added a nuance to these advantages, noting that the injector isn’t designed for the ab externo approach so this approach can sometimes be cumbersome to use; nevertheless, he added that it can readily be adapted with practice.
Dr. Do, Dr. Kim, and Dr. Panarelli now insert the XEN 45 using an ab externo approach almost exclusively. “I haven’t done any ab interno XEN cases since September 2018,” Dr. Kim said. “I’m not sure if this approach has a role for me anymore.”
Dr. Grover, however, still prefers the ab interno approach in patients with a prominent brow or sunken eyes, or in combination with cataract surgery when the eye has already been opened up. “I think it is essential to know how to comfortably perform the ab externo and ab interno techniques as sometimes, if the ab externo technique does not provide the ideal positioning for the XEN, I occasionally convert to an ab interno approach. Rarely, when using the ab externo approach, the XEN can be implanted too posteriorly and close to the iris. I then retrieve the device via an ab interno approach and reimplant via an ab interno approach.”
He therefore recommends that surgeons still learn the traditional ab interno approach first before “playing around” with ab externo techniques.
Dr. Do and Dr. Panarelli avoid this problem by having an open peritomy and direct visualization of the external tip of the XEN 45, allowing them to make micro-adjustments, pulling the stent out and pushing it into the anterior chamber to ensure that the stent is properly positioned in the intrascleral and sub-Tenon’s space. Ensuring ideal positioning of the distal end of the microstent beneath the Tenon’s layer and conjunctiva has resulted in surgical outcomes being more predictable, they said. Moreover, the blebs are more diffuse and posteriorly directed, and this improved bleb morphology makes them comfortable injecting higher concentrations of MMC. Their needling rate is less than 5%, and they have not had any erosions with their approach.

Expanding toolbox

Even as XEN use evolves, surgeons are already expectantly awaiting the FDA approval of another microsurgical glaucoma drainage device: the PreserFlo (formerly the InnFocus Microshunt, Santen Pharmaceutical). While we can postulate, Dr. Grover said that we don’t know yet how exactly these devices will fit together in the expanding glaucoma surgical toolbox. He was a primary investigator for the FDA trial on the InnFocus and speaks to the efficiency of this surgery as well. Moreover, what he does know is that the XEN has been a game changer; if and when the PreserFlo is approved, he thinks the device will be a game changer as well.
“We’ll have to play it by ear and determine which surgery is better for which patient, but I think the big theme is they both will be tremendous additions to our surgical armamentarium,” he said, adding, “The data coming out of Canada and the Dominican Republic with regard to PreserFlo are extremely encouraging and make most U.S. glaucoma doctors excited to get their hands on the PreserFlo.”

Editors’ note: The views expressed in this article attributed to Dr. Kim are his own and do not reflect the official policy of the Department of Army/Navy/Air Force, Department of Defense, or U.S. Government. The identification of specific products or scientific instrumentation is considered an integral part of the scientific endeavor and does not constitute endorsement or implied endorsement on the part of Dr. Kim, DoD, or any component agency. The views expressed in Dr. Kim’s interview are his own and do not reflect the official policy of the Department of Army/Navy/Air Force, Department of Defense, or U.S. Government.

Contact information

Do
: annado88@gmail.com
Grover: dgrover@glaucomaassociates.com
Kim: wonkim74@hotmail.com
Panarelli: joepanarelli@gmail.com

About the doctors

Anna Do, MD
Resident
New York Eye and Ear Infirmary of Mount Sinai
Icahn School of Medicine
New York

Davinder S. Grover, MD
Attending surgeon and clinician
Glaucoma Associates of Texas
Dallas

Won Kim, MD
Walter Reed National Military Medical Center
Bethesda, Maryland

Joseph Panarelli, MD
Associate professor of ophthalmology
Chief, Division of Glaucoma Services
New York University Langone
Eye Center
New York

Financial interests

Do: None
Grover: Allergan, Glaukos,
New World Medical
Kim: None
Panarelli: Aerie Pharmaceuticals, Allergan, Glaukos, New World Medical, Santen Pharmaceutical

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