Original articleXEN® Gel Stent for management of chronic open angle glaucoma: A review of the literature
Introduction
Glaucoma is a blinding optic neuropathy affecting nearly 60 million people world-wide. Among all forms of glaucoma, primary open angle glaucoma (POAG) is the most frequent etiology [1]. The therapeutic arsenal for POAG includes pressure-lowering medications, laser treatments and surgery. In France, the most commonly performed glaucoma surgeries are trabeculectomy [2] and non-penetrating deep sclerectomy (NPDS) [3]. These are both filtering surgeries whose basic premise is to lower intraocular pressure (IOP) by creating a pathway for release of aqueous humor from the anterior chamber (AC) of the eye into a subconjunctival space: the filtration bleb (FB). These filtering surgeries are effective but are accompanied by a non-negligible rate of complications such as postoperative hypotony, essentially for trabeculectomy, aqueous leak from the bleb, or even cataract [4], [5], [6]. Problems with conjunctival-Tenons scarring involve 25 to 30% of surgical patients [7] and are responsible for the majority of surgical failures. Finally, an infection of the filtering bleb, or “blebitis,” may occur, with a risk of endophthalmitis with a very unfavorable, but fortunately rare, prognosis. The cumulative incidence of endophthalmitis secondary to blebitis after trabeculectomy with mitomycin C (MMC) is between 0.4% (36-month follow-up) and 1.1% (5-year follow-up) [6], [7], [8].
Consequently, new techniques for decreasing the IOP have been developed so as to limit the intra- and postoperative complications of filtering surgery; these are known as MIGS (minimally invasive glaucoma surgeries). The exact characteristics qualifying a surgical technique as a MIGS have not achieved consensus. We may nonetheless consider MIGS as a surgical procedure designed to decrease IOP by increasing the outflow of aqueous less traumatically than classical filtering surgery, allowing for rapid recovery with a good safety profile [9]. Most often, these techniques are performed ab interno, not requiring a conjunctival opening, and are associated with cataract surgery [10]. XEN® is one of these new treatment options.
This technique consists of the ab interno implantation through the AC of a 6 mm long collagen tube with a 45 μm lumen, known as XEN®, placing the AC in communication with the subconjunctival space (Figure 1, Figure 2) [11], [12]. This surgery may be performed alone or at the same time as cataract surgery [13]. This new technique should avoid complications related to conjunctival dissection, as well as being more rapid [14]. Placement of a XEN® gel stent is currently indicated stand-alone surgery or in combination with cataract surgery for progressive mild to moderate open angle glaucoma uncontrolled on topical medications, with or without cataract. [13]. The XEN® received the CE mark in December 2015 and FDA approval in November 2016, and since then, several studies have been published.
The purpose of this literature review was to evaluate, through the publications on the subject, the safety and efficacy of this new technique. The data analyzed were the percentage IOP lowering at 1 year postoperatively, the decrease in number of glaucoma medications, the frequency of postoperative maneuvers, and the frequency and type of complications.
In April 2018, we performed a PubMed search, using the terms (glaucoma AND XEN®) OR (glaucoma AND micro-stent) OR (glaucoma AND gel implant) OR (MIGS AND XEN®). The references in the articles retrieved from this bibliographic search were also studied. We thus included in this literature review all the prospective and retrospective cohort studies which studied the effect of placement of a XEN® gel stent, whether combined or not with cataract surgery, on IOP in patients with primary or secondary open angle glaucoma. The case reports and cohort studies which did not report IOP, the number of medications used, the frequency of maneuvers or postoperative complications were not included.
Among the 86 articles identified on PubMed, we eliminated 75 in the screening step, either because they presented the stent with no patient follow-up (n = 37) or because they studied a different procedure (n = 17); 18 articles were case reports, and three were reviews of the literature. Three articles were eliminated during the step of reading the complete text, since they did not include our outcomes measures (Fig. 3: flow chart).
After screening and analysis of eligibility, eight articles published between 2016 and 2018 were retained, six regarding prospective studies [11], [12], [13], [15], [16], [17] and two regarding retrospective studies [14], [18]. There were no randomized controlled trials. The characteristics and populations of the various studies are summarized in Table 1.
The analyzed data involved 958 eyes of 777 patients. Two articles presented results for patients who underwent XEN® placement as a stand-alone procedure [14], [16], and two articles presented only patients who underwent combined surgery [12], [13]. The other four articles presented both stand-alone XEN® patients and patients with combined procedures [11], [15], [17], [18]. Four studies presented eyes naïve to any filtering surgery [13], [14], [15], [17]. Finally, one article addressed patients with refractory glaucoma [16]. The outcomes measures were variable depending on the study, but all reported preoperative and 12-month postoperative IOP, the number of glaucoma medications, postoperative maneuvers and complications encountered.
Section snippets
Surgical technique
Since the surgical technique is standardized, implantation varied very little from one study to the other. The procedure was performed under local anesthesia (topical, intracameral, sub-Tenons or peribulbar). After subconjunctival injection of 0.1 mL mitomycin C (MMC) diluted to 0.1 mg/mL (or 0.2 mg/mL in the study by Schlenker et al. [14]) in the superotemporal quadrant, a 1.8–2.2 mm inferotemporal corneal incision was made. A miotic was injected, then the AC filled with viscoelastic. The
Effect on IOP and number of medications
The various studies found a mean 12-month IOP between 13 and 16 mmHg. This represented an IOP reduction of 25 to 56% depending on the study. This decrease was accompanied by a decrease in the number of glaucoma medications in all the studies. The change in IOP and number of medications in the various studies are presented in Table 2 (Table 2 and Fig. 4). By using a weighted average of the IOP's in the various studies, the IOP reduction was 42% at 1 year (going from 25 mmHg preoperatively to 14
Postoperative maneuvers
Table 3 summarizes the frequency and type of postoperative interventions performed in the various studies presented. Needling was the most frequent maneuver performed, with a rate of 32% (0–43%). In total, 55 eyes (5.7%) required repeat filtering surgery by trabeculectomy, repeat XEN® implantation, placement of a Baerveldt valve or performance of a cyclodestructive procedure.
Two studies with a small study population reported a low number of postoperative maneuvers. Pérez-Torregrosa et al. [13]
Complications
The complications encountered are listed in Table 4. The most frequent were transient hypotony (< 1 month) (3%), the appearance of a choroidal effusion or choroidal folds, all transient (1.5%), hyphema (1.9%), Seidel sign (1.1%) and a flat anterior chamber (1.1%). Regarding serious complications, four cases of malignant glaucoma were reported in the study by Schlenker et al. [14] (0.4%), and one case of retinal detachment (0.1%) in that of Mansouri et al. [19]. No endophthalmitis was reported in
Disclosure of interest
The authors declare that they have no competing interest.
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