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Surgical innovations in glaucoma: Experiences and outcomes with Xen
Two early adopters of the device share their first results and tips for implantation.
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Andrew Scott is a glaucoma fellow at Moorfields Eye Hospital in London and, under the supervision of locum consultant ophthalmologist Ahmed Elkarmouty, has been an early adopter of the Xen injectable implant. In this article, Scott and Elkarmouty share their early experience with the Xen and give us their top tips for successful implantation of this innovative surgical modality.
Anthony Khawaja, PhD, FRCOphth
Outgoing Chair of the SOE Young Ophthalmologists committee
In May 2016, Xen, the first injectable gel implant for people with primary open-angle glaucoma who are not well managed on drops, was launched in the U.K. by Allergan. The ab interno implant creates a new subconjunctival outflow pathway to reduce IOP. We have been early adopters of this innovative surgical modality, and here we would like to share our experience, key learning points and early outcomes of our first 25 cases.
Patient selection
We offered Xen implantation to any patient who needed a first glaucoma operation. However, we believe that some groups may benefit more from this glaucoma procedure:
- Young patients whose fear of surgery steers them toward this shorter and less invasive surgical modality.
- Very old patients, especially those with significant cataracts, in whom a shorter combined procedure is an attractive option.
- Patients with back pain who cannot have general anesthesia and cannot tolerate a long time lying supine.
- High myopes who may be at risk of choroidals and macular folds with conventional trabeculectomy.
- Patients who express a wish to be drop-free in the long term or are not compliant with drops. The less invasive nature of this surgical modality may reduce the surgeon’s threshold for intervention.
- Patients with very friable conjunctiva in whom conventional trabeculectomy or tube insertion may be difficult.
Our experience with Xen
Of our first 25 patients, 14 were white, nine black and two Chinese, and their glaucoma was being treated on average by three drops. Mean IOP was 23 ± 8 mm Hg (range: 14 mm Hg to 40 mm Hg), and mean age was 72 ± 16 years (range: 39 years to 95 years).
All our surgery is performed under local anesthesia using a sub-Tenon block with lignocaine. We administer 0.1 mL of high-dose anti-scarring agent in the subconjunctival space before the procedure. We inject it at 12 o’clock and spread it across to the superonasal quadrant using spears. The patient then undergoes implantation.
The Xen implant is about 6 mm long and the width of a human hair. It is inserted with a small preloaded disposable 27-gauge injector via a small self-sealing corneal incision, ensuring the procedure is minimally invasive. The injector goes across the anterior chamber of the eye to the upper nasal quadrant. The Xen implant remains clear of the iris and corneal endothelium, and the injector enters through the trabecular meshwork, creating a scleral tunnel to the subconjunctival space. The implant is placed in the non-dissected Tenon space to join the anterior chamber to the subconjunctival space.
We are very aggressive with anti-inflammatory medication in the postoperative period. At the end of the procedure, we give our patients 40 mg triamcinolone in a sub-Tenon injection and prescribe 0.1% dexamethasone every 2 hours for up to 3 months after implantation. During the postoperative phase, we have a very low threshold for performing bleb needling and 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.
Outcomes
The graphs show the preop and postop IOP data collected so far. To date, numbers are small, especially for the 6-month time points.
- At 2 weeks, 25 patients showed IOP reduction of 9.4 mm Hg (95% CI 5.6–13.3, P = .0001).
- At 3 months, seven patients showed IOP reduction of 9.3 mm Hg (95% CI 5.8–12.7, P = .0006).
- At 6 months, four patients showed IOP reduction of 9.8 mm Hg (95% CI 0.8–18.7, P = .040).
Needling was performed in five patients: three white, two black and one who had undergone implantation combined with phaco. Shallow anterior chambers were noted in three patients postoperatively, which self-resolved after a few days. No maculopathy or choroidals were seen in any of the patients. Two patients required second Xen procedures, both of which were successful.
Top tips for optimum outcomes
Plan the implant location before incision, and make sure the area is marked at 3 mm from the limbus. This ensures that the tenon is not adherent to the episclera and prevents perforation by the needle when entering the subconjunctival space. It is also important to mark an area where there are no conjunctival vessels to minimize risk of hemorrhage, which may obscure needle entry into the subconjunctival space.
Beware of sleeve resistance when entering the anterior chamber, particularly in phakic eyes to avoid any damage to the lens. Always use pilocarpine drops before surgery in phakic eyes to minimize this risk.
Aim high (more anterior) when inserting the needle into the angle. Remember, viscoelastic deepens the anterior chamber considerably, and this may interfere with your judgement of the angle anatomy, particularly if the procedure is not carried out under direct visualization by a gonioscopy lens. If injected too posteriorly in the angle, the Xen may enter the iris root or may be too close to the iris, which may occlude its tip.
Use traction while advancing the needle through the sclera until the full bevel can be seen.
Remove traction and maintain slight forward pressure with the injector while delivering the implant through gentle actuation of the slider.
Note: The Xen gel implant can only be inserted by surgeons who have received the specialist Allergan 1:1 Xen training.
Conclusion
While we have been early adopters of this innovative technology, we are also cautious and have always put our patients’ safety and interests first. We obtain consent from all patients, and they are aware of the limited long-term data available for this product. We are still working out which patients may benefit most from this implant and how best to manage patients in the postoperative period. We also are waiting for more robust data from comparative randomized controlled trials to guide our practice.
For maximum benefits for patients and clinicians, it is important to recognize the need for specialist training before starting to implant the Xen. The success of the procedure is technique-dependent, and there is a learning curve to be mastered. With regular exposure to Xen surgery, careful instruction and the necessary support, the Xen gel implant could become a beneficial part of your hospital’s glaucoma armamentarium.
- For more information:
- Andrew Scott, MD, FRCOphth, MRCSEd, FEBO, PhD, an OSN Europe Edition Board Member, is a glaucoma fellow at Moorfields Eye Hospital, London. He can be reached at andrew.scott@moorfields.nhs.uk.
- Ahmed Elkarmouty, PhD, FRCOphth, is locum glaucoma consultant at Moorfields Eye Hospital, London. He can be reached at ahmed.elkarmouty@moorfields.nhs.uk.
Disclosures: Scott and Elkarmouty report no relevant financial disclosures.