As we work to stay ahead of glaucoma progression, we frequently encounter noncompliance with prescription eye drop regimens, and compliant patients who are unable to achieve optimal pressures with medication alone. As the disease grows more aggressive through time, even IOP that seems well controlled can worsen on our watch. All it takes is one deviation from the medication schedule or one financial problem that leads to an unfilled prescription, and the optic nerve is damaged.
Sometimes the best choice is surgery. That often means laser trabeculoplasty or trabeculectomy, but several minimally invasive glaucoma surgery (MIGS) devices are changing the surgical landscape. One such device is the XEN Gel Stent, which was developed by AqueSys and later acquired by Allergan. XEN earned FDA approval in November 2016 for the management of refractory glaucomas for patients whose previous surgical treatment has failed or those with primary open angle glaucoma, and pseudoexfoliative or pigmentary glaucoma with open angles that are unresponsive to maximum-tolerated medical therapy. I participated in the clinical trials for XEN and found that the device is simple and elegant, safe and atraumatic to the eye, and as effective as any other treatment at reducing IOP to the low teens.
EMPLOYING THE SUBCONJUNCTIVAL ROUTE
Traditional trabeculectomy is relatively high risk, high reward. By bypassing the trabecular meshwork to channel outflow to the subconjunctiva, it lowers IOPs significantly. However, results are variable. Trabeculectomy can lower IOP too quickly at first, causing discomfort and blurred vision; patients often require manipulation and fine-tuning after surgery. Complications are not uncommon.
Several less invasive MIGS procedures present less risk, but also less reward. Because they don’t bypass the eye’s outflow mechanism, they generally do not lower IOP as much as trabeculectomy.
The XEN Gel Stent provides an opportunity to employ a subconjunctival drainage pathway without incurring the risk, invasive dissection, or potential complication rate of trabeculectomy. It creates a gentle laminar flow of aqueous, so although it lowers IOP significantly, it doesn’t do so in a rapid manner that can cause complications. Patients see very well the day after XEN implantation, without much swelling.
IMPLANTING THE XEN GEL STENT
I find XEN implantation to be the most elegant glaucoma procedure to perform. The stent comes in a preloaded injector, similar to those used for intraocular lenses. I make a clear corneal incision with the injector, going through the anterior chamber and sclera and into the subconjunctival space. I push the injector’s button, delivering the stent to the needle track, where it connects the anterior chamber and subconjunctival space, and then I remove the injector. The small incision requires no sutures.
The XEN Gel Stent is composed of collagen-derived gelatin, engineered to a permanent form. The eye accepts the non-inflammatory, gelatin-based material without the problems that can occur with some synthetic materials. Just 6-mm long and the diameter of a hair, the hydrophilic tube quickly expands to form a soft, tissue-conforming drainage channel. This very straightforward implantation can be done alone or in conjunction with cataract surgery. Patients with XEN may undergo future posterior procedures to reduce IOP, if needed.
REVIEWING XEN CLINICAL DATA
In a prospective, multicenter, single-arm, open-label clinical trial of the XEN Glaucoma Treatment System (the XEN45 Gel Stent and the XEN Injector),65 patients were implanted with the stent.1 At 12 months, more than three quarters of those patients had a 20% or higher IOP reduction from baseline (mean medicated baseline 25.1 [+ 3.7] mmHg, compared with mean at 12 months of 15.9 [+ 5.2] mmHg). Overall, patients used fewer IOP-lowering medications, going from a mean of 3.5 at baseline to 1.7 at 12 months. The procedure was very safe.
Another recent study combined XEN with phacoemulsification for 30 eyes of patients using at least two IOP-lowering medications.2 These patients with mild to moderate open-angle glaucoma had a mean preoperative IOP of 21.2 mmHg (±3.4) with 3.07 medications. After phacoemulsification and XEN, IOP decreased 61.65% on day one, 31% at 6 months, and 29.34% at 12 months. Most patients were using no eye drops; the number of medications dropped to a mean of 0.16.
Although no treatment is guaranteed to obviate the need for eye drops, XEN’s potential efficacy makes it a realistic choice with the goal of reducing or eliminating the need for drops in the right candidates. Other procedures might just lower the IOP so patients can use fewer drops — a valuable change, particularly for advanced or complex cases — but I’ve had patients whose pressures dropped to the low teens with XEN, eliminating any need for drops. Patients appreciate that the reward for having surgery is drop independence.
LOOKING TOWARD THE FUTURE
The range of MIGS devices available today is exciting. We are finally getting the tools to fulfill that desire for a long-term way to manage glaucoma that doesn't require medication.
As I have become more comfortable using XEN on-label for patients with moderate disease, it seems like a benign step to move XEN to an earlier stage in the treatment algorithm. For patients who have some optic nerve damage and are only 40 or 50 years old, we might think about surgery right away to ensure that they maintain their vision decades into the future. Long-term follow-up data are needed, but perhaps we may, one day, follow our European counterparts and move XEN to a first-line treatment, rather than an option to employ only after medications have failed to achieve our goals. We may be able to intervene surgically as soon as we become aware of compliance-related challenges, rather than after noncompliance results in permanent damage.
The number one goal is to lower pressures, and if we have a device that does all the work, it’s a win-win for patients and surgeons. GP
- FDA. 510(k) Summary: XEN Glaucoma Treatment System. Nov. 21, 2016. Accessed online Jan. 24, 2017. https://www.accessdata.fda.gov/cdrh_docs/pdf16/K161457.pdf
- Pérez-Torregrosa VT, Olate-Pérez Á, Cerdà-Ibáñez M, et al. Combined phacoemulsification and XEN45 surgery from a temporal approach and 2 incisions. Arch Soc Esp Oftalmol. 2016;91(9):415-421.