Management of fracture and displacement of a previously successful bilateral transconjunctival ab-externo XEN gel stent: a case report

Abstract

Background

The XEN45 Gel Stent (XGS) is an innovative, minimally invasive glaucoma surgery device, which is typically inserted via an ab-interno method, avoiding conjunctival dissection. With increasing experience, some surgeons have advocated for a transconjunctival ab-externo approach, with or without conjunctival dissection, for the delivery of XGS.

Case presentation

A 33-year-old male patient with a history of primary open-angle glaucoma diagnosed three years ago presented to the clinic with the complaint of visual field loss. This case report presents the initial implantation of XGS in both glaucoma eyes, using the transconjunctival ab-externo technique without conjunctival dissection. However, subsequent follow-up revealed that in the left eye, the XGS had been fractured as a result of external force. Meanwhile, in the right eye, the displacement of the XGS was attributed to the surgical needlework. To facilitate re-implantation, the transconjunctival ab-externo approach with conjunctival dissection was employed to enhance the securement of the XGS.

Conclusions

The case highlights that external force and needling can cause XGS fracture and displacement. To reduce this risk, employing a transconjunctival ab-externo approach with conjunctival dissection and securing the XGS with sutures was found to decrease complications, indicating a more effective surgical strategy for XGS implantation.

Introduction

Recently, the field of glaucoma treatment has welcomed the dawn of Minimally Invasive Glaucoma Surgeries (MIGS). These procedures are designed to minimize the intrusiveness while effectively lowering intraocular pressure (IOP), thus reducing the risks associated with intra and postoperative complications, while also promoting faster recovery times [1, 2]. The XEN45 Gel Stent (XGS) (XEN^® gel stent, Allergan) is one of the new commercially available MIGS devices made of porcine gelatin, draining the aqueous from the anterior chamber to a subconjunctival filtration bleb, thus bypassing conventional outflow pathways [3].

The XGS is designed and approved for an ab-interno approach. Generally, this approach obviates the necessity for conjunctival dissection, whether implemented as an independent procedure or in combination with phacoemulsification [4]. However, as surgeons have accumulated more extensive experience with XGS, some have chosen to utilize an ab-externo approach. This approach may involve either an open conjunctiva delivery of the device or implantation without conjunctival dissection. Despite being off-label, the ab-externo approach offers several substantial advantages. These include minimal manipulation of the anterior chamber, avoidance of corneal incisions, the optional use of viscoelastic, and a decreased risk of the stent’s distal end becoming embedded in Tenon’s capsule [5,6,7].

Clinical research on XGS implantation has indicated promising results in terms of reducing IOP and decreasing reliance on topical medications, regardless of whether the implant was placed via an ab-interno or an ab-externo approach [8]. However despite the positive surgical outcomes of the XGS, complications have been recorded in cases with the ab-interno surgical technique [9–10]. To date there are very few reports addressing the complications of transconjunctival ab-externo XGS. Here, we report a case of the management of fracture and displacement of a previously successful bilateral transconjunctival ab-externo XGS.

Case presentation

Case description

A 33-year-old male patient was referred to the clinic with the complaint of loss of visual field. A previous diagnosed of primary open angle glaucoma (POAG) was made 3 years ago. Upon examination, the IOP readings (Goldmann applanation tonometry) were 23 mmHg in the right eye (OD) and 17 mmHg in the left eye (OS) despite maximum anti-glaucoma medication (tafluprost, carteolol, brimonidine, and brinzolamide). Pachymetry measurements showed a central corneal thickness of 572 μm in OD and 570 μm in OS, respectively. High myopia was detected in both eyes, with a spherical equivalent refraction of -13.00 diopters measured without cycloplegia. His best corrected logMAR visual acuity was 0.8 in OD and 0.1 in OS. Gonioscopy showed open angles in both eyes. The anterior segment examination was unremarkable. Fundus exam showed a cup-to-disk ratio (C/D) of approximately 0.9 in both eyes. Recent visual fields test revealed nasal step defect with a mean deviation (MD) value of 11.6 dB in OD and partial arcuate defect with an MD value of 19.7 dB in OS. OCT showed significant retinal nerve fiber layer (RNFL) thinning, with an average RNFL thickness of 54 μm in OD and 52 μm in OS. Due to the unsatisfactory IOP control and progressive visual field deterioration, surgical intervention was considered (Fig. 1).

Fig. 1

Clinical presentation. (A) Fundus photos of the right (A1) and the left eye (A2) showed marked cupping, notching of blood vessels, and thinning of neuroretinal rim at the upper and lower poles. (B) Visual field testing showed nasal step defect in the right (B1) and partial arcuate defect in the left eye (B2). (C) Retinal nerve fiber layer thickness in the right (C1) and left eye (C2) measured by OCT examination

Surgical procedure for initial transconjunctival ab-externo XGS implantation

After a thorough discussion of the risks and benefits of possible surgical options, the patient gave his written informed consent for the proposed XGS surgery. He underwent an uneventful XGS implantation in OS, and then had the same procedure in OD 6 weeks later. A proficient surgeon (KJ. Wang) performed an ab-externo XGS implantation using a transconjunctival technique, without conducting conjunctival dissection.Briefly, the conjunctiva was marked at 2 millimeters (mm) and 5 mm behind the limbus at the 11 o’clock position to indicate the implantation site. Under topical anesthesia, a mixture of 0.4 mg/mL mitomycin c and 2% lidocaine was injected at the intended area. A corneal traction suture was placed in the superior cornea to facilitate the downward rotation of the eye. The XGS injector was placed bevel up, with its tip inserted into the conjunctiva at 5 mm from the limbus; then tilted downwards at 2 mm from the limbus and advanced through the scleral tunnel until it penetrated 1 mm into the anterior chamber. The length and placement of the XGS within the angle can be verified using a gonioscopy lens. Once the XGS was fully released, the outflow of the aqueous humor was confirmed and a diffuse bleb was promptly established following the forced infusion of a balanced salt solution. Post-surgical treatment involved the administration of pranopulin, tobramycin and dexamethasone eye drops four times daily.

Management of XGS fracture in the left eye

The surgical procedure was successful in both eyes, with an IOP stabilizing at 15.5 mmHg in OD and 15.5 mmHg in OS, respectively, without the necessity for supplementary drops at 1 and 2 months postoperatively. However, at 3 months after XGS implantation in OS, the IOP increased to 57 mmHg due to an injury from a child’s kick, and still remained at 29 mmHg after needling and anti-glaucoma eye-drop treatments (tafluprost, carteolol, and brinzolamide). During the slit lamp examination, except for the absence of the XGS beneath the filtering bleb, the other structures of the eye showed a relatively normal state. The cornea was clear and transparent. The conjunctiva was without any significant bleeding or discharge. A clear anterior chamber with a normal depth was observed. The iris and pupil were in normal positions, and the pupillary light reflex was sensitive. During gonioscopy, the tip of the XGS projecting into the anterior chamber was not visible in OS.

To further explore the position of the drainage tube, we performed a filtering bleb separation exploration in OS. During the procedure, the conjunctival sac was meticulously incised, and the Tenon’s capsule surrounding the XGS was carefully separated. The terminal end of the XGS was clearly visible upon inspection. Surprisingly, the XGS removed from the scleral tunnel was only 2 mm in length (Fig. 2A, B), which was significantly shorter compared to its initial implanted length. A thorough examination of the adjacent conjunctival tissue revealed no remnants of the previous XGS, indicating that the XGS may have shifted to other unknown areas.

Fig. 2

Intraoperative and postoperative photographs of the displaced Xen gel stent (XGS) in left eye. (A) Blue pentagram indicates the distal end of the XGS after opening the conjunctival sac. (B) Green triangle indicates the residual end of the XGS with a length of merely 2 mm. (C) A new XGS was implanted with a 10 − 0 nylon encircling suture was placed approximately 3 mm posterior to the limbus to secure the XGS without occluding it. (D) Slit-lamp examination showed an approximately 4 mm of the XGS was observed within the anterior chamber in the left eye

Consequently, a new XGS was implanted through an open conjunctiva, transconjunctival ab-externo placement approach. In brief, the injector was positioned 2 mm from the limbus and the needle was advanced superficially until it penetrated the anterior chamber. A 10 − 0 nylon encircling suture was placed approximately 3 mm posterior to the limbus to secure the XGS without occluding it (Fig. 2C). The outflow of aqueous humor was verified by visualizing beading at the distal end of the XGS. The length and position of the XGS were adjusted to ensure a 1 mm penetration into the anterior chamber. Then the Tenon’s layer and conjunctiva were closely sutured. On the first postoperative day, the IOP was 12 mmHg in OS.

At 1 month after the implantation of a new XGS in OS, the patient returned to the clinic for a routine follow-up examination. During the slit-lamp examination, an approximately 4 mm of the XGS was observed within the anterior chamber in OS (Fig. 2D), with an IOP of 20 mmHg in OD and 16.5 mmHg in OS. We conducted a third surgical procedure on the patient’s left eye to extract the XGS from the anterior chamber.

Management of XGS displacement in the right eye

During the 3-month post-operative follow-up visit for the patient’s OD surgery, the IOP increased to 27 mmHg, accompanied by conjunctival adhesion to the implant. Consequently, a needling procedure was scheduled. Briefly, a 30-G needle attached to a 1.0 mL syringe was utilized to penetrate the conjunctiva in the superotemporal region, approximately 10 mm away from the XGS. The tip of the needle was carefully advanced beneath the conjunctiva and employed to puncture the fibrosis surrounding the tube through lateral sweeping motions, moving back and forth and above and below the XGS. The aim of this procedure was to free the tip of the implant from any adhesions. A positive indication is when the implant can move freely under the conjunctiva.

Two weeks later, upon conducting a slit-lamp examination of the right eye, it was found that the XGS had shifted into the anterior chamber (Fig. 3A). As a result, an XGS adjustment surgery became necessary for the patient’s right eye.

Fig. 3

Slit-lamp examination and intraoperative photographs of displaced and fractured Xen gel stent (XGS) in the right eye. (A) Slit-lamp examination showed the XGS had shifted into the anterior chamber. (B) Blue pentagram indicates the distal end of the XGS after opening the conjunctival sac. (C) The distal end of the stent was found to be obstructed by a substantial accumulation of pigments. (D) The fragile stent was fractured by the tweezers. (E) The fractured XGS. (F) A new XGS was implanted with a 10 − 0 nylon encircling suture was placed approximately 3 mm posterior to the limbus to secure the XGS without occluding it

During the surgical procedure, the conjunctiva and Tenon’s capsule were meticulously dissected to expose the XGS. The distal end of the XGS was found to be obstructed by a substantial accumulation of pigments (Fig. 3B, C). We endeavored to clear the obstruction within the XGS, but unfortunately, the fragile XGS was fractured by the tweezers (Fig. 3D, E). Therefore, we had to remove the entire XGS, and implant a new one through an open conjunctiva, transconjunctival ab-externo placement approach. Under gonioscopic examination, the new XGS was found to be positioned with its end extending 1 mm into the anterior chamber. The XGS was sutured to the scleral surface using 10 − 0 nylon suture to ensure enhanced fixation and prevent displacement (Fig. 3F).

Surgical outcomes during follow-up

The patient achieved satisfactory IOP levels during the follow-up period. The IOP was 13.5 mmHg in OS and 17.5 mmHg in OD, at 4 months and 2 months after the last surgery, respectively. The best corrected logMAR visual acuity was 0.8 in OD and 0.1 in OS. The tip’s length and position were perfectly suited in the anterior chamber under gonioscopy (Fig. 4A). Slit-lamp examination and anterior segment optical coherence tomography revealed a well-functioning bleb (Fig. 4B, C).

Fig. 4

Postoperative XEN gel stent (XGS) position and the bleb morphology. (A) Blue arrows indicate XGS under gonioscopy examination in the right eye (A1) and the left eye (A2). (B) The bleb morphology observed using slit-lamp photography exhibits characteristics of a localized avascular nature in the right eye (B1) and the left eye (B2). (C) The bleb morphology observed using anterior segment optical coherence tomography (OCT) demonstrates characteristics of a high sparse wall type. Please note that blue dashed lines represent the same location of the OCT section in the right eye (C1) and the left eye (C2)

Discussion

In this case report, the initial surgical method selected for the implantation of the XGS in both eyes involved a transconjunctival ab-externo approach without conjunctival dissection. During the follow-up period, the XGS in OS suffered a fracture caused by an external force (a kick from a child). In OD, the XGS was displaced due to the needling procedure. Upon re-implantation, we employed the transconjunctival ab-externo approach with conjunctival dissection.

Studies have compared the advantages, disadvantages, and clinical outcomes of the ab-interno and the transconjunctival ab-externo approach, as well as the ab-externo approach with and without conjunctival dissection. Table 1 provides a brief comparison of the three surgical methods advantages and their disadvantages [4,5,6]. Certain studies have indicated that the XGS demonstrates comparable efficacy, with similar postoperative IOP control, medication reduction, incidence of complications, and bleb revision rates of different implantation methods in patients with POAG [6, 7, 11, 12]. However, some other studies have reported different outcomes. Helwe et al. found that XGS using a transconjunctival ab-externo approach with conjunctival dissection may result in a more significant reduction in IOP when compared to ab-interno approach [7]. Ucar et al. proposed that the implantation of XGS through a transconjunctival ab-externo approach without the conjunctival dissection, significantly reduced the rate of postoperative needling compared to the ab-interno method [12]. In contrast, Tan and colleagues observed similar rates of needling in both the ab-interno and the transconjunctival ab-externo groups with conjunctival dissection [13]. Helwe et al. demonstrated that both transconjunctival ab-externo techniques, with and without conjunctival dissection, effectively reduce medication use and IOP. However, the transconjunctival ab-externo approach with conjunctival dissection showed higher success rates and superior IOP control, despite requiring a longer procedure time and increased use of 5-FU [14]. The transconjunctival ab-externo approach without conjunctival dissection is faster, sutureless, and minimizes the impact on conjunctival quality, which is beneficial for future trabeculectomy or glaucoma drainage device implantation procedures. By comparison, the transconjunctival ab-externo technique with conjunctival dissection provides superior control over bleb formation and aqueous outflow direction, potentially offering additional IOP reduction benefits due to improved outflow dynamics and bleb morphology after conjunctival dissection [4, 14]. In this case, the initial surgical method selected for both eyes was a transconjunctival ab-externo approach without conjunctival dissection, followed by a second transconjunctival ab-externo approach with conjunctival dissection. Both methods yielded favorable postoperative IOP outcomes.

Table 1 Comparison of advantages and disadvantages of Xen implantation surgery methods

The XGS is designed to undergo a slight expansion within 1 to 2 min post-implantation, adopting a flexible and tissue-conforming property intended to minimize the risk of implant migration. Once implanted, it assumes an “S” curve within the scleral channel, thereby effectively anchoring the implant in position. However, despite these design features, there have been reports of XGS via ab-interno approach forward into the anterior chamber during patient follow-up [9, 15,16,17]. Gilmann et al. reported a case of XGS via ab-interno approach dislocation into the anterior chamber, with localized corneal damage. Moreover, they speculated three theories regarding the displacement of XGS, including eye rubbing, alleviating scar formation due to the application of MMC, and inertial forces generated by ocular movements [15]. Menchini et al. present a case of a complete dislocation of the XGS into the anterior chamber, accompanied by a decrease in endothelial cell density. They highlighted the importance of measuring the length of the free-tube segment within the anterior chamber and assessing endothelial cell density at every visit [16]. At present, this case represents an instance where the XGS was fractured due to external force, and after needling (with eye rubbing possibly being a contributing factor), the XGS became displaced. Consequently, during the re-implantation of the XGS, we fixed it with sutures to ensure its securement, which may minimize its displacement.

Similar to conventional filtering surgeries, this operation can lead to the formation of a subconjunctival bleb, which may be prone to subsequent fibrosis. In such cases, needling may be performed, either alone or in combination with the use of antimetabolites. Previous studies report that the probability of needle puncture ranges from 27.9 to 51.3% [5, 12, 18]. Despite the lack of a standardized timeline for conducting needling after XGS implantation, it is crucial to remain vigilant to prevent treatment failures caused by subconjunctival fibrosis [19]. Gallardo et al. suggested that the detection of XGS curvature indicates the beginning of early fibrosis. It is believed that prompt needling upon observing any XGS curvature can effectively reduce the risk of treatment failure [11]. However, it is crucial to recognize that the needling process can potentially cause XGS breakage and displacement [15, 20, 21]. Therefore, when performing the needling procedure in patients after a XEN implantation, it is important to maintain a clear visualization and exercise caution to prevent any damage to blood vessels [20, 21].

Conclusions

External force and needling may lead to the fracture and displacement of the XGS. The adoption of a transconjunctival ab-externo approach with conjunctival dissection and securing the XGS with sutures can enhance its stability and reduce the risk of dislocation.