Scleral tunneling combined with the Tenon’s capsule coverage in Glaucoma Drainage Valve surgery

Abstract

Objective

To evaluate the clinical efficacy of an modified surgical technique using scleral tunneling and Tenon’s capsule for implantation of the Ahmed Glaucoma Drainage Valve (AGV) in refractory glaucoma.

Methods

This research involved the retrospective collection of data from 78 patients diagnosed with refractory glaucoma who underwent implantation of the AGV using a modified technique combining scleral tunneling with autologous Tenon’s capsule. The analysis focused on preoperative and 60-month postoperative indices, which included the surgical technique employed, intraocular pressure (IOP) measurements, the utilization of antiglaucoma medications, rates of surgical success, and the incidence of postoperative complications.

Results

The findings suggest that the modified surgical technique exhibited an accuracy in the placement of implants. It also achieved remarkable postoperative control of IOP. The average IOP of the enrolled patients decreased from a preoperative maximum of 44.5 mmHg to 18.62 mmHg at 60 months postoperatively. Additionally, the usage of antiglaucoma medications decreased from an average of 2.88 preoperative medications to 1.76 medications at 60 months postoperatively. The rates of surgical success were recorded at 85.90% at 12 months, 82.54% at 24 months, 76.60% at 36 months, 71.88% at 48 months, and 66.67% at 60 months following the surgical procedure. It is noteworthy that no severe complications, including drain valve exposure and endophthalmitis, were reported.

Conclusions

The modified AGV implantation technique effectively regulated IOP, reduced medication dependence, and minimized severe complications. However, limitations such as small sample size and lack of a control group necessitate further large-scale trials to confirm its efficacy.

Introduction

The implantation of the AGV has emerged as a principal therapeutic intervention for refractory glaucoma, particularly in cases where traditional filtration surgery has proved ineffective [1,2,3]. Despite its effectiveness, complications such as low IOP, shallow anterior chamber, choroidal detachment, drainage valve malposition, corneal endothelial damage, fibrous encapsulation of the filtration channel, and drainage valve exposure can still occur following AGV implantation.

The exposure of drainage valves is recognized as a particularly challenging postoperative complication associated with AGV implantation, when compared to other glaucoma surgical procedures. This complication predominantly arises from insufficient coverage of the conjunctiva or the Tenon’s capsule, particularly in the region of the drainage tube. Such inadequacies can lead to serious adverse outcomes, including endophthalmitis [4,5,6].

Numerous surgical modifications have been explored to mitigate potential risks, including the use of the AGV in conjunction with allogeneic scleral flaps, allogeneic pericardium, or alternative biomaterials [4, 7, 8]. Nevertheless, these coverages are accompanied by certain risks, including restricted availability of donors, the possibility of rejection responses, and the potential for postoperative complications.

In this study, based on our previous transscleral tunnel implantation method for covering and fixing the drainage tube [9], we propose a modified surgical approach that uses the patient’s own isolated Tenon’s capsule to cover the surface of the AGV, aiming to prevent AGV tube exposure in patients with refractory glaucoma.

Methods

Study patients

This study analyzed the clinical data of 78 patients with refractory glaucoma who underwent implantation of the AGV at The First Affiliated Hospital of Fujian Medical University between April 2018 and December 2023. The patients’ ages ranged from 21 to 83 years, with a mean age of 55.44 ± 15.51 years. The cohort comprised 33 females and 45 males. The study was approved by the Institutional Ethics Committee of the First Affiliated Hospital of Fujian Medical University (No. IEC-FOM-013-2.0) and conducted in accordance with the latest version of the Declaration of Helsinki. Informed written consent was obtained from all of the participants in the study.

Refractory glaucoma enrolled in this study including primary closed-angle glaucoma (13 eyes, 16.7%), primary open-angle glaucoma (6 eyes, 7.7%), traumatic glaucoma (2 eyes, 2.6%) and mixed glaucoma (2 eyes, 2.6%). Neovascular glaucoma accounted for another proportion of cases, with diabetic retinopathy being the most common cause (39 eyes, 50.0%), followed by retinal detachment (5 eyes, 6.4%), uveitic glaucoma (5 eyes, 6.4%) and retinal vein occlusion (6 eyes, 7.7%).

Surgical indications

The indications for AGV implantation included neovascular glaucoma secondary to conditions such as diabetic retinopathy or retinal vein occlusion, failed previous glaucoma surgeries (e.g. trabeculectomy), advanced POAG uncontrolled by medical therapy, uveitis glaucoma, traumatic glaucoma resulting from ocular injury, and mixed-mechanism glaucoma with combined features of several types of glaucoma.

Exclusion criteria for surgery

In this study, we clarified the exclusion criteria to ensure the accuracy and reliability of the study. The exclusion criteria were as follows: (1) patients with active inflammation or other serious eye diseases; (2) those with suboptimal compliance who were unable to effectively participate in the required ophthalmological examinations and subsequent follow-ups; (3) patients with systemic diseases, such as serious insufficiency of the heart, liver, kidneys, and other vital organs; (4) pregnant women, lactating women, or patients with psychiatric disorders; and (5) patients with incomplete baseline information who could not provide complete medical records. These criteria were designed to exclude patient groups that could influence the outcome of the trial and the analysis of the data, thus improving the validity of the study results.

Surgical technique

This study details a modified surgical technique that has been used in our department’s clinical practice since 2018. The technique involves scleral tunneling combined with the Tenon’s capsule for AGV implantation in all patients.

The surgical procedure was conducted in the following manner: Patients were placed in a supine position, and the operative eye was subjected to standard sterilization and draping protocols. A retrobulbar block anesthesia was administered using 2% lidocaine, and a speculum was employed to maintain the eyelids in an open position. A curved incision was executed along the scleral margin at the bulbar junction, accompanied by radial incisions at both extremities of this incision on the bulbar conjunctiva, with cauterization utilized to manage hemostasis.

The AGV model FP7 (New World Medical Inc., Rancho Cucamonga, CA, USA) was surgically positioned in a supratemporal location in all subjects’ eyes. The insertion of the AGV into the drainage port was facilitated using a blunt needle filled with saline, which was subsequently injected to prime the shunt. Successful initialization of the device was verified by the observation of fluid flow from the drainage system.

The AGV implant was placed in a temporal position relative to the conjunctiva and subcapsular to Tenon’s capsule. It was secured to the sclera approximately 8 to 10 millimeters from the limbus utilizing a 6 − 0 non-absorbable suture. The drainage tube was trimmed to facilitate insertion into the anterior chamber by 2 to 3 millimeters, featuring a beveled edge for optimal placement.

A 23-gauge needle was inserted into the anterior chamber at a distance of 4 mm from the superior temporal limbus, oriented parallel to the iris. A lengthy submerged scleral tunnel, approximately half the thickness of the sclera, was created. Sodium hyaluronate was then administered into the anterior chamber and the drainage device was positioned along this tunnel, extending approximately 2–3 mm into the anterior chamber, taking care to avoid contact with either the corneal endothelium or the iris.

To anchor the drain and ensure its stability, an “8” configuration suture was used with an 8 − 0 absorbable suture. This suture was placed 6 mm from the corneal limbus on the superficial sclera, not ligating but securing the tube, preventing it from being displaced or eroded through the conjunctiva. The suture is tied in such a way that it supports the tube without obstructing the flow of aqueous humour, thus maintaining the functionality of the AGV implant.

The Tenon’s capsule beneath the incision was meticulously dissected to envelop the surface of the drainage valve and subsequently secured to the superficial sclera using 8 − 0 absorbable sutures. The conjunctival flap was then closed utilizing interrupted 10 − 0 non-absorbable sutures. Following the procedure, Tobramycin-dexamethasone ophthalmic ointment was administered to protect the operated eye (see Fig. 1).

Fig. 1

Surgical Technique for Scleral Tunneling Combined with Tenon Coverage in Glaucoma Drainage Valve Surgery. A-C: Initial conjunctival and scleral incisions are made at the bulbar junction, with radial incisions at both ends for exposure. D-E: The AGV implant is placed in a supratemporal position, secured to the sclera 8–10 mm from the limbus with a 6 − 0 non-absorbable suture. F-G: A scleral tunnel is created using a 23-gauge needle, extending from the scleral surface into the anterior chamber, approximately half the thickness of the sclera. H: Insertion of the drainage tube into the anterior chamber through the scleral tunnel, taking care not to contact the corneal endothelium or the iris. I: Applying an “8” suture configuration with an 8 − 0 absorbable suture to anchor the tube to the superficial sclera, 6 mm from the corneal limbus. J: Dissection of the Tenon’s capsule under the incision to cover the AGV implant, secured with 8 − 0 absorbable sutures. K: Closure of the conjunctival flap with interrupted 10 − 0 non-absorbable sutures. L: Postoperative appearance showing the covered AGV implant with no visible exposure

All surgeries were performed by the corresponding author of this study, Dr Wang Xiaohui, a highly experienced ophthalmologist with over 25 years of clinical experience in glaucoma management and surgery.

Post-operative management

All patients received standardised postoperative pharmacotherapy: (1) Antibiotic prophylaxis with 0.5% levofloxacin eye drops (Cravit^®, Santen) four times daily for 2 weeks; (2) anti-inflammatory therapy with 1% prednisolone acetate (Pred Forte^®, Allergan) tapered from eight to two times daily over 6 weeks, combined with NSAIDs (Pranoprofen eye drops^®, Senju) twice daily for 3 months; (3) IOP-lowering medications were used if IOP exceeded 21 mmHg.

Patients were examined preoperatively and at various follow-up times ranging from 1 day to 60 months postoperatively (specific follow-up times are shown in Fig. 2) and IOP was measured with a non-contact tonometer (TOPCON). Postoperative follow-up was performed by the surgeon. All patients were examined postoperatively using a slit-lamp microscope to examine the operated eye and a funduscope or SLO to determine the fundus condition. The above observations and the use of postoperative antiglaucoma medications, adverse events or reoperations were carefully recorded after surgery.

Fig. 2

The mean preoperative and postoperative IOP in this study. Error bars indicated standard deviations. The mean preoperative IOP was 46.40 ± 10.61 mmHg and decreased significantly to 17.70 ± 4.75 mmHg at the last follow-up. IOP showed a significant reduction at all postoperative time points: 16.19 ± 3.45 mmHg at 12 months, 17.29 ± 3.89 mmHg at 24 months, 17.73 ± 4.81 mmHg at 36 months, 18.25 ± 3.88 mmHg at 48 months, and 17.70 ± 4.75 mmHg at 60 months, achieving an overall reduction rate of 61.85%

Definition and criteria for surgical success

Criteria for the evaluation of the surgical outcome were defined as follows:1. Complete success: IOP was controlled within the target range of 6–21 mmHg without the need for additional topical glaucoma medications or further glaucoma surgery. 2. Conditional success: IOP was controlled within the target range of 6–21 mmHg with the use of additional topical glaucoma medications.3. Failure: IOP remained above 21 mmHg despite the addition of topical anti-glaucoma medication, or significant complications occurred that affected the surgical outcome. The overall surgical success rate was calculated as the sum of the complete and conditional success rates.

Statistical analysis

Statistical analyses were performed using SPSS 26.0. Continuous variables were compared via paired t-test or Wilcoxon signed-rank test as appropriate. Longitudinal medication patterns were assessed using Friedman test with post-hoc Dunn-Bonferroni correction. Effect sizes calculated using Cohen’s d. Two-tailed p < 0.05 defined significance.

Results

IOP

The cohort demonstrated sustained IOP reduction throughout the 60-month follow-up. Mean IOP decreased from 46.40 ± 10.61 mmHg preoperatively to 17.70 ± 4.75 mmHg at final follow-up (mean difference: 28.7 mmHg, 95% CI 26.3–31.1; paired t-test t = 21.34, p < 0.001). Temporal analysis revealed significant reductions at all postoperative intervals: 16.19 ± 3.45 mmHg at 12 months (p < 0.001), 17.29 ± 3.89 mmHg at 24 months (p < 0.001), 17.73 ± 4.81 mmHg at 36 months (p < 0.001), 18.25 ± 3.88 mmHg at 48 months (p < 0.001), and 17.70 ± 4.75 mmHg at 60 months (p < 0.001). The overall IOP reduction rate reached 61.85% (see Fig. 2).

Antiglaucoma medications

Prior to surgery, patients were utilizing an average of 2.9 ± 0.7 antiglaucoma medications. This number decreased to 1.7 ± 1.0 at the 12-month follow-up, 1.8 ± 1.1 at 24 months, 1.8 ± 0.9 at 36 months, 1.9 ± 1.0 at 48 months, and 1.8 ± 0.8 at 60 months postoperatively (see Fig. 3).

Fig. 3

The mean number of preoperative and postoperative medications used for patients. Error bars indicated standard deviations. ± Before surgery, patients were taking an average of 2.9 ± 0.7 antiglaucoma medications. This number decreased significantly to 1.7 ± 1.0 at 12 months, then fluctuated slightly to 1.8 ± 1.1 at 24 months, 1.8 ± 0.9 at 36 months, 1.9 ± 1.0 at 48 months and 1.8 ± 0.8 at 60 months postoperatively, reflecting a sustained reduction in medication dependence after surgery

Success rate

The overall success rate of AGV surgeries was recorded at 85.90% at the 12 months, which subsequently declined to 82.54% at 24 months, 76.60% at 36 months, 71.88% at 48 months, and 66.67% at 60 months. The rates of complete success were observed to be 33.33%, 28.57%, 14.89%, 12.50%, and 23.81% at the corresponding time intervals. In contrast, the conditional success rates were documented as 52.56%, 53.97%, 61.70%, 59.38%, and 42.86% across the same periods (see Fig. 4).

Fig. 4

Success rate following Ahmed glaucoma valve implantation. The overall success rate at 12 months postoperatively was 85.90% and gradually decreased to 82.54% at 24 months, 76.60% at 36 months, 71.88% at 48 months and 66.67% at 60 months. Complete success rates, defined as IOP within target range without additional medication or surgery, were 33.33%, 28.57%, 14.89%, 12.50% and 23.81% at each of these intervals. Conditional success rates, which include patients who required additional medication to achieve IOP control, were 52.56%, 53.97%, 61.70%, 59.38% and 42.86% for the corresponding periods. These data reflect the durability and efficacy of AGV implantation using our modified surgical technique

Complications

Postoperative complications were observed in 38.5% of the patients, which included hyphema (10.3%), shallow anterior chamber (9.0%), choroidal detachment (7.7%), encapsulated cyst (5.1%), tube malposition (3.8%), and iris tube occlusion (2.6%) (see Fig. 5). All complications were addressed through conservative management, and no reoperations were necessary. Additionally, there were no reported cases of postoperative diplopia, strabismus, tube erosion or exposure, or endophthalmitis.

Fig. 5

Postoperative complications and management after modified AGV implantation. All complications were managed conservatively without reoperation. CI: confidence interval

Discussion

The AGV, which was introduced thirty years ago, has emerged as the most prevalent glaucoma drainage implant, especially in cases of refractory glaucoma. While the efficacy of AGV implantation in managing refractory glaucoma is well-documented, numerous early and late postoperative complications have been identified, one of which is drain exposure resulting from conjunctival perforation [1]. The techniques for implantation have undergone significant advancements, with the management of drain exposure being a critical consideration in the implantation of AGV. Initially, the drain tube was primarily inserted into the anterior chamber through direct puncture behind the limbus, and various graft materials, including allogeneic scleral implants and pericardium, were utilized to cover the exposed portion of the tube on the scleral surface [10]. These coverings are faced with varying degrees of rejection, such as scarce sources, time-consuming and costly retrieval processes, imperfect implant preservation techniques, and even the risk of implant contamination leading to endophthalmitis.

In recent years, to solve the problem of complications, especially drainage valve exposure, an increasing number of researchers have proposed using the Tenon’s capsule separation and folding to cover the body of the drainage valve to minimise the risk of exposure [11, 12]. Nonetheless, challenges persist concerning the preparation of scleral flaps. Intraoperative detachment of a scleral flap that is either excessively thick or insufficiently thin may result in various complications, including tearing of the scleral flap or complete penetration of the sclera, potentially harming intraocular tissues. Compared to Tamçelik et al.‘s Tenon’s advancement method, our technique provides dual mechanical-biological protection through scleral tunneling combined with autologous Tenon’s grafts, achieving none tube exposure at 60 months follow-up, while demonstrating applicability in patients with compromised Tenon’s integrity.

Our improved technique showed an overall success rate of 66.67% at 60 months, which is not less than conventional AGV implantation methods reported in the literature. For example, a 5-year follow-up study of conventional AGV with mitomycin-C for glaucoma showed an overall success rate of 57 ± 7% [13]. In the Romanian cohort, the 5-year success rate of standard AGV for refractory glaucoma was 60% [14]. There is a significant difference in the long-term success rate of AGV implantation using conventional methods, which may be related to postoperative complications such as drain exposure and migration [15, 16]. In our study, we observed that the modified technique has a significant advantage in reducing these serious complications, which may help improve the long-term success rate.

Fewer complications may have improved surgical success rates. To counteract the potential for drainage valve exposure, we utilized the patient’s own Tenon’s tissue as a protective covering, ensuring that the tube remains distanced from the conjunctiva throughout its length, thereby safeguarding it against mechanical injury. As the drain passes through the patient’s own Tenon’s capsule tissue, this helps to reduce inflammatory or immune responses to the foreign material, for example reducing the risk of allograft rejection. This reduces the likelihood of rejection and inflammation due to an immune response. At the conclusion of the follow-up period, while 38.5% of participants experienced postoperative complications, it is noteworthy that none of the patients in this study encountered severe complications. The complete absence of tube exposure in our cohort contrasts favorably with historical AGV exposure rates of 5.8-12.4% using conventional scleral flap techniques [17,18,19]. This improvement likely stems from the dual protective mechanism of our technique: (1) the scleral tunnel provides biomechanical stabilization exceeding donor scleral grafts and (2) autologous Tenon coverage eliminates antigenic risks inherent in allografts.

An additional benefit of this methodology is that the tube traverses the patient’s own Tenon’s capsule, thereby mitigating the risk of inflammation or immune responses to foreign materials, such as the rejection of allografts [4, 18, 20, 21]. By creating tunnels within the sclera and partially burying the drains within them, we provide additional biomechanical stability to the drains. This stability exceeds what can be achieved using a donor scleral graft and helps to reduce drain displacement and exposure. Additionally, the application of an “8” suture, located 6 mm from the corneoscleral limbus, enhances the stability of the drainage valve, thereby restricting its mobility and partially regulating drainage. This approach is instrumental in preventing premature overfiltration and providing an additional layer of protection to the tube, reducing the risk of tube exposure and subsequent complications.

It is essential to consider the following aspects during the intraoperative phase of the surgical technique employed in this study. Following the conjunctival incision, it is crucial to ensure that the space between the Tenon’s capsule and the sclera is adequately distanced to enable the implantation of the drainage valve, as well as the subsequent separation and suturing of the Tenon’s capsule. In the process of constructing the scleral tunnel, a submerged puncture should be executed between the layers of the sclera to provide the surgeon with a clear view of the superficial sclera and to maintain visibility of the puncture needle’s channel [7, 22]. As the puncture needle nears the anterior chamber angle, it is essential to adjust its position to maintain parallel alignment with the iris plane, thereby facilitating the puncture of the anterior chamber while avoiding any harm to the corneal and iris tissues. The puncture should be executed in a single, fluid motion rather than through a series of repetitive sawing actions, as the latter technique may inadvertently enlarge the puncture site and exacerbate peritubular leakage. However, this technique, like other AGV surgeries, has some drawbacks, including a shallow anterior chamber and even postoperative choroidal leakage [23, 24].

In cases where the depth of the anterior chamber is insufficient, a lateral corneal incision may be performed, followed by the injection of balanced salt solution or sodium hyaluronate into the anterior chamber to aid in its formation. It is imperative to implant the drainage tube with care, ensuring that it is not held with excessive force to avoid any risk of breakage or deformation. The tapered end of the tube should be oriented towards the cornea to assess for potential obstructions at the tube’s opening. This positioning will also facilitate subsequent interventions, such as the laser removal of any obstruction at the tube opening or the irrigation of the tube lumen via a limbal incision using a needle.

In certain older patients, the attenuation of the Tenon’s capsule may complicate the separation process and restrict the applicability of this technique. Additionally, individuals who have experienced multiple prior surgical interventions may present with the Tenon’s capsule that is either excessively thin or unevenly distributed, further constraining the utilization of this method.

Although this study highlights the potential benefits of the modified AGV implantation technique, several limitations must be acknowledged. The retrospective, single-center design, combined with a moderate sample size (n = 78), limits the generalisability of our findings to broader populations and may reduce the statistical power to detect rare adverse events. The lack of a control group, particularly those undergoing standard AGV implantation or alternative procedures, prevents direct comparisons of efficacy and safety. In addition, the retrospective nature of the study introduces potential selection bias, as variability in preoperative disease severity and postoperative management protocols may influence the interpretation of results. Although our 60-month follow-up provides valuable mid-term data, the long-term durability of IOP control and the safety profile, especially with regard to late complications such as tube erosion or corneal endothelial damage, remain to be fully established. These limitations highlight the need for future multicentre, prospective studies with standardised protocols, matched controls and longer follow-up to fully validate the clinical utility of this modified technique.

Conclusions

In summary, the scleral tunnel technique, when utilized in conjunction with the Tenon’s capsule separation cover as proposed in this study, demonstrates efficacy and safety for the implantation of AGV and the prevention of tube exposure in individuals suffering from refractory glaucoma. This method is characterized by its simplicity, cost-effectiveness, and broad applicability. Nonetheless, it is important to exercise caution when applying this procedure to patients with thin conjunctiva or Tenon’s capsule, in order to assess its long-term safety and effectiveness.