ORIGINAL ARTICLE |
https://doi.org/10.5005/jp-journals-10078-1443 |
Ab Externo Transconjunctival XEN® 45 Gel Stent Implantation: Efficacy and Safety of a New Surgical Technique
1,3–5Department of Ophthalmology, Hospital of San Severino Marche, AV3- Asur Marche, Macerata, Italy
2Department of Ophthalmology, IRCCS - San Raffaele Hospital, Milan, Lombardy, Italy
Corresponding Author: Edoardo Cavallero, Department of Ophthalmology, IRCCS - San Raffaele Hospital, Milan, Lombardy, Italy, Phone: +39 02 26433589, e-mail: edoardo.cavallero1986@gmail.com
Received: 18 October 2023; Accepted: 20 June 2024; Published on: 29 October 2024
ABSTRACT
Aim: To evaluate the efficacy and safety of XEN® 45 gel stent implantation with a new surgical approach by ab externo transconjunctival technique.
Materials and methods: A total of 31 eyes of 31 patients affected with primary open-angle glaucoma (POAG) were treated with an ab externo transconjunctival approach. All the XEN gel stent implantations were performed at the Department of Ophthalmology of the Hospital of San Severino Marche, AV3- Asur Marche, Macerata, Italy between January 2021 and May 2021, and the follow-up duration was at least 6 months.
Results: A total of 31 eyes of 31 patients (mean age 65.6 ± 12.3 years; 20 males and 11 females) were included in the study. All the patients were affected by POAG. The mean intraocular pressure (IOP) was 25.3 ± 3.8 mm Hg, and the mean number of IOP-lowering topical medications before surgery was 2.7 ± 0.9. No intraoperative complications were reported. During the follow-up, one patient received medical treatment for a choroidal detachment, one patient had a 2 mm hyphema, and one patient had a partial migration of the stent in the anterior chamber. At the 1-month follow-up, the mean IOP was 12.8 ± 2.5 mm Hg and no patient was on IOP-lowering treatment, while at the 3-month and 6-month follow-ups, four patients were on treatment with one IOP-lowering drug. During the follow-up period, seven patients required postsurgical bleb needling, and one patient underwent a revision with PreserFlo® Microshunt implantation. The final mean IOP was 15.9 ± 2.7 mm Hg, and 27 out of 31 patients had an IOP of <18 mm Hg.
Conclusion: Ab externo transconjunctival XEN® 45 gel stent implantation represents a safe and effective surgical treatment approach.
Clinical significance: The ab externo approach represents a safe and effective technique, allowing early surgical timing and widening the group of patients who could benefit from the filtrating surgical technique before many years of topical medical treatment, which causes marked conjunctival alteration.
Keywords: Ab externo transconjunctival surgical approach, Glaucoma surgery, Microinvasive glaucoma surgery, Primary open-angle glaucoma, XEN® 45 gel stent implantation
How to cite this article: Pirani V, Cavallero E, Cesari C, et al.Ab Externo Transconjunctival XEN® 45 Gel Stent Implantation: Efficacy and Safety of a New Surgical Technique. J Curr Glaucoma Pract 2024;18(3):94–97.
Source of support: Nil
Conflict of interest: None
INTRODUCTION
Primary open-angle glaucoma (POAG) represents the second leading cause of global irreversible blindness, with an estimated prevalence of 112 million people in 2040.1 POAG is a progressive optic neuropathy that leads to the death of the optic nerve’s ganglion cells with a corresponding loss of visual field. The pathogenesis of glaucomatous damage has not been completely explained, while there is agreement in considering intraocular pressure (IOP) elevation as the only modifiable risk factor. The European Glaucoma Society (EGS) guidelines recommend starting with a monotherapeutic IOP-lowering medical treatment followed eventually by laser treatment to reach the target pressure. However, different works and daily clinical practice have demonstrated that the continuous use of IOP-lowering topical drugs could damage the ocular surface, significantly decreasing the patient’s compliance.2,3 Laser treatment, although a hypotensive activity could be demonstrated in almost 70% of patients, has limited efficacy over time and there is a risk of inflammatory transient pressure spikes.4,5 Surgery is the therapeutic option in cases of low adherence to medical treatment or in cases of uncontrolled IOP after using the maximum topical drugs. Trabeculectomy is still considered the gold standard of surgical treatment regarding hypotensive efficacy, but over time it can have some important severe complications, such as choroidal detachment or intraocular hypotension, sometimes irreversible.6,7 In the early 2000s, different types of procedures were developed so that pressure-lowering surgery could be performed through a microincisional approach without disturbing the conjunctiva. These procedures were termed ”microinvasive glaucoma surgery” (MIGS), and they work in various ways: by decreasing resistance to outflow at the level of the trabecular meshwork (TM), inserting a shunt into the suprachoroidal space, or creating a shunt into the subconjunctival space. These surgical procedures have demonstrated the ability to reduce IOP by a modest amount and have a very reasonable safety profile.8
The XEN® 45 is a 6 mm long hydrophilic tube with an internal diameter of 45 µm made of porcine gelatin cross-linked with glutaraldehyde to limit the surrounding tissue reaction. It creates a permanent channel through the sclera, allowing for controlled passage of aqueous humor from the anterior chamber to the subconjunctival space. By providing a new outflow route, the XEN® 45 decreases the accumulation of aqueous humor and lowers IOP.
We present a retrospective review of a new surgical technique of XEN® 45 gel stent implantation by ab externo transconjunctival approach, aiming to minimize intraoperative and postoperative complications.
MATERIALS AND METHODS
This is a retrospective analysis of 31 eyes of 31 patients who underwent XEN gel stent implantation by a single surgeon (VR) using a new ab externo transconjunctival approach at the Department of Ophthalmology of Hospital of San Severino Marche, AV3- Asur Marche, Macerata, Italy from January to May 2021. The study was conducted in accordance with the standards of the 1964 Helsinki Declaration and its later amendments. All participants provided informed consent for the retrospective review of medical records, and all data collection was performed confidentially, following the minimum necessary standard. All patients had a diagnosis of POAG and had uncontrolled IOP, progressing glaucoma, and/or intolerance to topical hypotensive drugs. Exclusion criteria included eyes previously treated with any glaucoma surgery or a history of uveitis. All patients were phakic. At the preoperative and postoperative visits, all patients underwent a complete ophthalmological examination including Snellen best-corrected visual acuity (BCVA), slit-lamp examination, measurement of IOP, and fundus examination. IOP was measured using Goldmann applanation tonometry. Glaucoma medications were counted as the number of individual hypotensive agents or oral acetazolamide.
Patients were evaluated postoperatively at 1 day, 1 week, 1, 2, 3, and 6 months. The principal outcomes were the success rate of surgery, defined by an IOP <18 mm Hg, the rate of intraoperative and postoperative complications, and the decrease in the number of glaucoma medications.
Statistical calculations were performed using the Statistical Package for the Social Sciences (SPSS) (version 17.0, SPSS Inc., Chicago, Illinois, United States of America). All quantitative variables were presented as mean and standard deviation in the results and tables. Comparisons of mean IOP between baseline and different follow-up times were performed using the Student’s t-test. The chosen level of statistical significance was p < 0.05.
Surgical Technique
XEN® 45 is precolored by Trypan Blue to enhance visibility in the anterior chamber and subconjunctival space, especially in cases of subconjunctival hemorrhages (Fig. 1A). After topical anesthesia, the bulbar conjunctiva is carefully lifted in the superotemporal quadrant, and a preloaded injector needle is inserted through the conjunctiva 8 mm from the corneal limbus, laterally from the insertion site into the anterior chamber (Fig. 1B); the preloaded injector needle is advanced between the tenon capsule below and the mobile conjunctiva above, proceeding until 2 mm from the limbus (Fig. 1C); the patient is instructed to look downward, guiding the needle into the anterior chamber and keeping it parallel to the iris before releasing XEN® 45. Subsequently, the position of the needle tip is carefully observed using indirect gonioscopy to ensure it is anterior to the pigment trabecular meshwork. After releasing XEN® 45, the tube in the anterior chamber is adjusted under the conjunctiva to achieve an optimal length of 1–2 mm (Figs 1D and E). A low-intensity diathermy is then performed near the insertion site in the conjunctiva to reduce the risk of Seidel’s phenomenon. Finally, a subtenonian injection of 0.2 mL of a solution of mitomycin-C (MMC) 0.1 mg/mL is administered at 8–10 mm from the limbus (Fig. 1F). The injection of MMC is delayed until the end of the surgical procedure to avoid altering the virtual space between the conjunctiva and tenon capsule. Care is taken to ensure that the insertion of the stent occurs above the tenon capsule. To minimize the risk of fibrotic processes of the filtering bleb, all patients underwent a subconjunctival injection of an anti-fibrotic agent, 5-fluorouracil, 15 days after the surgical intervention.
Figs 1A to F: (A) XEN® 45 is precolored by Trypan Blue; (B) Bulbar conjunctiva is carefully lifted in the superotemporal quadrant and a preloaded injector needle is inserted through the conjunctiva at 8 mm from corneal limbus; (C) The preloaded injector needle is pursued between the tenonian capsule below and the mobile conjunctiva above; (D) XEN® 45 in the anterior chamber is regulated throughout the conjunctiva until an optimal length of 1–2 mm; (E) XEN® 45 correctly positioned in the anterior chamber observed by indirect gonioscopy; (F) Subtenonian injection of 0.2 mL solution of MMC 0.1 mg/mL done at 8–10 mm from the limbus
RESULTS
A total of 31 eyes of 31 patients (mean age 65.6 ± 12.3 years; 20 males and 11 females) were followed up for at least 6 months after ab externo transconjunctival XEN® 45 gel stent implantation. All patients had POAG and were phakic. The mean preoperative IOP was 25.3 ± 3.8 mm Hg, and the mean number of glaucoma medications was 2.7 ± 0.9. No intraoperative complications were reported. After 1 month, the mean IOP decreased to 12.8 ± 2.5 mm Hg (p = 0.009) (Table 1) and no patients were on IOP-lowering treatment. At the 3- and 6-month follow-ups, four patients were on treatment with one IOP-lowering medication (Fig. 2). During the follow-up period, one patient received medical treatment for choroidal detachment, one patient had a 2 mm hyphema, and one patient experienced partial migration of the stent into the anterior chamber. Additionally, seven patients required postsurgical bleb needling, and one of these seven patients underwent a revision with PreserFlo® Microshunt implantation. The final mean IOP was 15.9 ± 2.6 mm Hg (p = 0.038) (Table 1) and 27 out of 31 patients had an IOP <18 mm Hg (Fig. 3).
| Baseline | 1 month | 2 months | 3 months | 6 months | |
|---|---|---|---|---|---|
| IOP (mm Hg) | 25.3 ± 3.8 | 12.8 ± 2.5 | 14.2 ± 3.8 | 12.9 ± 2.9 | 15.9 ± 2.7 |
| p-value | 0.009 | 0.029 | 0.014 | 0.038 |
Fig. 2: Number of patients under IOP-lowering therapy before surgical treatment (baseline) and at different follow-up times after ab externo transconjunctival XEN® 45 gel stent implantation
Fig. 3: Number of patients with IOP <18 mm Hg before surgical treatment (baseline) and at different follow-up times after ab externo transconjunctival XEN® 45 gel stent implantation
DISCUSSION
This retrospective analysis demonstrated the efficacy and safety profile of the new surgical approach using ab externo transconjunctival technique, particularly in young phakic patients whose eyes have been relatively spared from prolonged use of glaucoma topical medication.
The ab externo transconjunctival approach proves to be less traumatic by avoiding procedures in the anterior chamber, which can be potentially dangerous for the iris and the lens. It also reduces injury to the blood-aqueous barrier, resulting in lower production of aqueous humor rich in proinflammatory and profibrotic factors for the filtering bleb.
At the beginning of the ab externo surgical technique, neither anesthetic drugs nor MMC were injected into the subconjunctival space. Care was taken to place the stent in the space between the tenon capsule below and the mobile conjunctiva above. This correct placement of the stent is challenging to achieve in the ab interno technique.
Performing low-intensity diathermy at the conjunctival insertion point of the needle reduces the risk of transconjunctival Seidel’s phenomenon.
Recently, some studies have demonstrated that various ab externo approaches with XEN stent implantation may be not inferior to the traditional ab interno approach in terms of efficacy and safety.
Tan et al. evaluated the safety and efficacy differences between the ab interno and ab externo approaches for XEN gel stent implantation, analyzing 50 eyes that underwent ab interno placement and 30 eyes that underwent ab externo placement. The authors found no significant differences in outcomes between ab interno and ab externo placement of the XEN gel stent and concluded that both approaches demonstrated similar safety and efficacy for lowering IOP. Bleb needling was performed on 42% of eyes in the ab interno cohort and 26.7% of eyes in the ab externo cohort.9
These data are similar to our series, where five out of 31 eyes (16.1%) required postsurgical bleb needling after 2 months and two out of 31 eyes (6.5%) after 3 months. This finding could be related to the 45 µm internal diameter of the XEN gel stent implantation, which is associated with a flow rate through the device of 1.2 mL/minute, lower than the basal aqueous production of 2–3 mL/minute. This results in a decrease in aqueous supply, reducing the presence of proinflammatory and profibrotic factors and lowering the risk of bleb fibrosis, particularly in the early postoperative period.
Scheres et al. compared the long-term efficacy and safety of the XEN® 45 gel stent implant and the PreserFlo® MicroShunt. Regarding postoperative complications, the authors described in the XEN group, six cases (15%) of stent curling. Specifically, in one patient, the stent migrated toward the anterior chamber, necessitating repositioning in the operating room.10
Differently from other authors, in our series, only one patient experienced partial migration of the stent into the anterior chamber.
Purgert et al. conducted a retrospective analysis comparing outcomes of ab interno and ab externo XEN implantation, evaluating 36 and 19 eyes, respectively, that underwent the two different techniques. The authors demonstrated the efficacy of both approaches to XEN gel stent implantation for glaucoma management, achieving similar IOP reduction and medication reduction at 6 months. Interestingly, they found that the ab externo approach had the additional benefit of reducing early postoperative bleb needling.11
Similarly to the current data, at the 6-month follow-up, mean IOP decreased by >35% compared to the baseline value, with 85% of patients completely free from glaucoma medications (Fig. 2).
This study has several limitations, the most significant being its retrospective nature; therefore, our results should be interpreted and evaluated within the context of this design. Additionally, the sample size was relatively small, and the postoperative follow-up period was limited to 6 months after surgical treatment. Another limitation is the ethnic homogeneity of the sample, as all patients were Caucasians, which restricts the generalizability of our findings to other ethnic populations. Further studies with longer follow-up periods and larger patient cohorts are necessary to validate our findings comprehensively.
CONCLUSION
The ab externo surgical approach represents a less invasive technique for creating a subconjunctival filtering bleb and can be considered safe and effective compared to the ab interno approach. It better respects the biological and structural integrity of the eye.
This technique should be considered in young, phakic patients with preserved structural conjunctiva, unaffected by inflammatory processes.
Due to its safety and effectiveness, coupled with its low invasive profile, the ab externo approach could enable earlier surgical intervention and expand the patient population benefiting from filtering surgical techniques, thus potentially mitigating the marked conjunctival alterations associated with prolonged topical medical treatments.
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