Comparison of Tenon duplication with dura mater covering technique for Ahmed glaucoma valve implantation

Abstract

Purpose:

To compare the efficacy and complications of Tenon duplication with dura mater covering technique for Ahmed glaucoma valve (AGV) implantation.

Methods:

This retrospective study included 44 refractory glaucoma patients (44 eyes) who underwent AGV implantation from 2017 to 2020 in the Ophthalmology Clinic of Eskişehir Osmangazi University Hospital and attended regular postoperative follow-ups. The patients were divided based on whether they underwent Tenon duplication technique (group 1: n = 20) or dura mater covering technique (group 2: n = 24) during surgery. The patients’ age, gender, systemic diseases, glaucoma type, pre-op intraocular pressure (IOP), and ocular surgeries were recorded. The groups were compared for IOP level control, early and late complications, postoperative antiglaucomatous medication requirements, glaucoma surgery requirements, presence of postoperative hypertensive phase (HP), and surgical success which was defined as an IOP ≥5 and ≤21 mmHg, with or without antiglaucoma medication.

Results:

By the end of the mean follow-up (22.6 ± 10.6 months), the success rates were 95% (group 1) and 96% (group 2). The groups showed no differences in postoperative complications, postoperative antiglaucomatous drugs’ onset time, additional glaucoma surgery, need for needling, presence of HP at 6 months postoperatively, and relationship between the glaucoma type and success rates (P values: 0.86, 0.9, 0.48, 0.12, 0.36, and 0.8, respectively). The IOP values at the last follow-up were 15.2 ± 4.1 in group 1 and 14.7 ± 4.8 in group 2. The IOP reduction rates showed no significant differences.

Conclusion:

Since success and complications are similar in both Tenon duplication and dura mater covering technique, unique grafting materials may not be needed in AGV implantation surgery, except in special cases.

Glaucoma, the second most important cause of blindness globally, is defined as a chronic optic neuropathy with progressive visual field defects. Although many risk factors, such as intraocular pressure (IOP),[1,2,3] age,[2,3,4] genetic predisposition,[5] and vascular parameters,[6,7,8] have been identified for the development and progression of glaucoma, lowering IOP is the only scientifically proven method to slow progression.

IOP reduction in glaucoma patients can be achieved with medical, laser, or surgical treatment.[9] Medical treatment is usually the first choice because of the low rate of side effects, whereas laser or surgical option can be considered when the target IOP cannot be achieved.[10] Trabeculectomy, first described by Cairns in 1968, is considered the “gold standard” surgery for primary open-angle glaucoma.[11] However, the success rate of trabeculectomy, although high in the first years (70%–92%), tends to decrease over time (42%–90%), especially in secondary glaucomas.[12,13,14,15,16] Trabeculectomy is also greatly affected by the healing processes of the subconjunctival space in the bleb region. Therefore, modulation of recovery with intraoperative and postoperative antimetabolites (mitomycin C [MMC] and 5-fluorouracil [5-FU]) is an essential part of the procedure.[15,16]

Glaucoma drainage devices (GDDs) provide an alternative to traditional filtration surgery for the treatment of medical therapy–resistant glaucomas and in patients with conjunctival problem.[17] As a working principle, shunting aqueous humor (AH) into the posterior subconjunctival space can prevent healing problems, especially in patients who have had previous glaucoma operation or conjunctival scar. Although the implant types vary, Ahmed glaucoma valve (AGV) is the most commonly used implant option.[18] AGV minimizes the risk of hypotonia by allowing AH above a certain pressure to flow through a silicone tube placed in the anterior chamber toward a pressure-controlled valve mechanism consisting of a polypropylene plate sutured to the sclera in the sub-Tenon space. The most important problems with AGV implantation are tube exposure, encapsulation, and postoperative hypertensive phase (HP).[19] Tube exposure usually occurs 3–4 mm posterior to the corneoscleral limbus. Since this complication will have serious consequences leading to the loss of the eye, it should be treated quickly or preventive measures should be taken during surgery. Various covering techniques and graft materials have been developed to avoid tube exposure, including scleral tunnel, Tenon duplication, pericardial patch grafts, cadaveric dura mater, donor fascia lata graft, and preserved human sclera and cornea.[20] Although there are many comparative studies on tube covering techniques such as scleral flap and scleral tunnel techniques, pericardium, and lyophilized sclera, there are limited reports on dura mater covering and Tenon duplication techniques in AGV implantation surgery.[21,22] The present study compares the Tenon duplication technique and dura mater covering in terms of postoperative complications and the success rate.

Methods

This retrospective study included 44 eyes of 44 patients with refractory glaucoma who underwent AGV implant surgery between June 2017 and June 2020 in the Ophthalmology Department of Eskişehir Osmangazi University Hospital. Due to the retrospective nature of the study, patients who were followed up regularly were included in the study. Cases followed for at least 1 year were included in the study. Pediatric cases, patients with irregular follow-up, and those who were not in compliance with their medications were excluded from the study. The patients were divided into a group that underwent the Tenon duplication technique (Group 1) and a group that underwent the dura mater covering technique during surgery (Group 2). Each patient’s age, gender, systemic diseases, glaucoma type, previous surgical interventions, and IOP values were recorded. The two groups were compared for IOP, early and postoperative complications, needing antiglaucomatous medications and glaucoma surgery, and presence of an HP in the first 6 months postoperatively.

Surgery

AGV (New World Medical Inc., Rancho Cucamonga, CA, USA) Model FP7 was used in all eyes. A limbus-based superotemporal conjunctival flap was created 5 mm away from the limbus, between two adjacent rectus muscles, and extended to 90°. The rectus muscles were identified. Before placement of the tube implant, the tube was irrigated with saline solution to open the valve mechanism. The implant’s polypropylene body was sutured to sclera with 6-0 polyglactin sutures. The tube was fixed to the sclera with 10-0 nylon cross sutures. The anterior chamber was entered from 2 mm posterior to the corneoscleral limbus using a 23-gauge needle. The needle tract was anterior and parallel to the plane of the iris. The tube was then trimmed, so that the bevel faced the corneal endothelial surface. In group 1, the Tenon and the overlying conjunctiva were bluntly dissected at the posterior edge of the conjunctival flap and a separate Tenon flap was fashioned. The flap was pulled forward to cover the tube completely and sutured at the corneoscleral junction with 7-0 polyglactin or 10-0 nylon suture. Then, the right and left margins of the Tenon flap were sutured to the sclera with 7-0 polyglactin sutures, two on each side. At the last stage, the anterior edge of the conjunctival flap was pulled down together with the Tenon layer and sutured to the posterior conjunctival margin with continuous 7-0 or 8-0 polyglactin sutures [Video Clip 1].[23] In group 2, dura mater graft (Tutoplast dura; IOP, Inc., Costa Mesa, CA, USA) was covered over the tube and sutured to the sclera with 10-0 nylon suture. The conjunctiva was mutually sutured in a fluid-tight manner. All the eyes received subconjunctival injections of steroids and antibiotics after the operation.

Criteria for success

The surgical success criterion was determined as a postoperative IOP value between ≥5 and ≤21 mmHg, with or without antiglaucomatous therapy, measured at the last follow-up. The definition of hypotonia in this study was an IOP of 5 mmHg or less in more than two consecutive visits.

Statistical analysis

IBM Statistical Package for the Social Sciences (SPSS) version 22.0 (IBM Corp., Armonk, NY, USA) was used for statistical analyses. Summary values of quantitative (numeric) variables were shown as mean ± standard deviation or median (Q1–Q3), and summary values of qualitative (categorical) variables were shown as frequency and percentage. The conformity of quantitative variables to normal distribution was investigated using the Shapiro–Wilk test. Since a normal distribution was not found, two independent groups were compared using the Mann–Whitney U test. The relationship between qualitative variables was evaluated with Chi-square analysis (Fisher’s exact test). Quantitative values obtained from IOP measurements were assessed with repeated measures analysis of variance (repeated measures ANOVA). The significance of the main effects (group and measurement times) and the interaction term (group × time) were evaluated. Survival rates were compared with Kaplan–Meier analysis. Values of P < 0.05 were considered statistically significant.

Results

A total of 44 eyes of 44 patients were included in the study, and 20 eyes in group 1 and 24 eyes in group 2 were evaluated. Table 1 shows the demographic characteristics of the patients.

Table 1.

Demographic characteristics of the patients

		Group 1		Group 2		P
Number of patients (n)		20		24		-
Age (years)		60.5±15.8		54.8±23.3		0.361a
Gender (F/M)		11/9		7/17		0.002b
Follow-up time (months)		16.8±13.3		27.3±16.5		0.027a
Systemic disorders
DM		6 (30%)		0		0.003b
HT		2 (10%)		5 (20.8%)
DM + HT		6 (30%)		2 (8.3%)
Glaucoma subtype
POAG
SG		5 (25%)		3 (12.5%)		0.005b
NVG		11 (55%)		7 (29.2%)
XFG		4 (20%)		11 (45.8%)
Congenital		0		3 (12.5%)
Previous surgery
PHACO		8 (40%)		6 (25%)		0.369b
TRAB		2 (10%)		5 (20.8%)
PPV		4 (20%)		1 (4.2%)
PHACO + TRAB		2 (10%)		3 (12.5%)

^aIndependent samples t-test. ^bChi-squared test. DM=diabetes mellitus, HT=arterial hypertension, NVG=neovascular glaucoma, PHACO=phacoemulsification surgery, POAG=primary open-angle glaucoma, PPV=pars plana vitrectomy, SG=secondary glaucoma, TRAB=trabeculectomy surgery, XFG=exfoliation glaucoma

At the end of the mean follow-up period of 22.6 ± 10.6 months, the success rates were 95% in group 1 and 96% in group 2. No difference between the groups was detected with regard to postoperative complications, postoperative antiglaucoma medications onset time, need for needling, tube exposure, encapsulation, and presence of HP. (P-values: 0.47, 0.86, 0.12, 0.27, 0.9, 0.51 respectively) [Table 2]. The IOP values at the last visit were 15.2 ± 4.1 in group 1 and 14.7 ± 4.8 in group 2. The IOP reduction rates also showed no significant difference between the groups [Table 3].

Table 2.

Postoperative complications

		Group 1		Group 2		P
Hypertensive phase (n)		8 (40%)		12 (50%)		0.507
Postoperative complications (total) (n)		7 (35%)		11 (45.8%)		0.467
Hyphema		1 (5%)		2 (8.3%)		0.662
Iris–lens touch		2 (10%)		4 (16.7%)		0.521
Choroidal detachment		3 (15%)		4 (16.7%)		0.88
Tube exposure		1 (5%)		0		0.268
Tube occluded by vitreous		0		1 (4.2%)		0.356
Encapsulation		1 (5%)		1 (4.2%)		0.895
Needling requirement		4 (20%)		10 (41.7%)		0.124
Hypotonia		0		0		1

Statistical analysis was conducted with the Chi-square test

Table 3.

Intraocular pressure reduction rates between groups

		Group 1		Group 2		P
Pre-op IOP (mmHg)		31.2±8.3		33.9±7.8		0.25
Post-op first IOP (mmHg)		11.6±5.5		12.4±6.6		0.26
Post-op last IOP (mmHg)		15.2±4.1		14.7±4.8		1

Statistical analysis was conducted with the Pearson Chi-square test. IOP=intraocular pressure

Analysis of the success rates according to the last examination pressure and HP in the first 6 months postoperatively based on previous surgery history before trabeculectomy revealed no significant differences (P-values: 1 and 0.39, respectively). No statistically significant differences were found in the comparative analysis of these same parameters with the type of previous surgery (P-values: 0.36 and 0.47, respectively). In terms of surgical techniques, no significant difference was observed in the statistical analyses of postoperative HP and antiglaucomatous onset time (P-values: 0.36 and 0.89, respectively). Group 2 showed a higher HP percentage, but no statistically significant difference was detected when evaluating postoperative complications, success according to the last examination pressure, and HP in the first 6 months according to the glaucoma type (P-values: 0.92, 0.71, and 0.39, respectively). Although the need for needling was seen more in the dura mater covering technique, this was not statistically significant (P = 0.124). There was no difference in survival rate over time between the two groups (P values in log rank: 0.968, Breslow: 0.611, and Tarone–Ware: 0.718). It was estimated that hypertensive recurrence would not occur for a median (95% confidence interval [CI], Low–Upp) of 24 (21.92–26.08) months in patients with Tenon duplication and 16 (8.54–23.46) months in patients with dura mater covering technic [Fig. 1]. No vision loss was observed in any of the patients at their final follow-up.

Figure 1.

Means and medians for survival time with Kaplan–Meier analysis

Discussion

Filtering surgery is usually the first surgical option for glaucoma treatment. GDDs, such as AGV, are often an option available to patients with glaucoma refractory to filtering surgeries.[24] Although GDDs have been used frequently for years to reduce eye pressure, complications of AGV, such as tube exposure, choroidal detachment, hyphema, iris–lens touch, and encapsulation, can occur. Ou et al.[25] reported that the most common complication after AGV implantation in patients with primary congenital glaucoma was tube–corneal touch. Tube exposure is also a significant AGV implantation problem, as it leads to both mechanical damage and inflammation-mediated melting of the self-tissue or the donor graft. Inferiorly placed implants, diabetes, presence of prior inflammation, previous ocular surgery, and younger age are well-known risk factors for tube exposure associated with GDDs.[19,26] In addition, there are studies claiming that previous eye surgery is not a risk factor for exposure.[27] Untreated cases of tube exposure are well known to lead to possible endophthalmitis, with a poor prognosis. Recognizing these complications of AGV tube, we investigated the methods and modifications that could potentially prevent exposure and maintain IOP reduction during the postoperative period.

Although a number of surgical methods have been described to prevent tube exposure, such as placement of patch graft (e.g., fascia lata, pericardium, donor sclera, or lyophilized dura mater), lengthy scleral tunnel, and/or duplication and advancement of Tenon’s tissue, there is no consensus on the best approach. Tamcelik et al.[23] divided their patients into three groups according to the covering techniques used during AGV implantation. They did not see any exposure in the Tenon duplication group and claimed it to be the safest method. Gedar Totuk et al.[28] tried to prevent AGV tube exposure by creating a long scleral flap augmented with Tenon advancement and duplication; they had no exposure in the 2-year follow-up. Since an exposure case was seen in the Tenon duplication group in our study, it can be thought that adding the long scleral flap technique to the Tenon duplication technique may have an effect on reducing exposure. However, long scleral tunnel or scleral flap techniques are not ideal for all cases, such as in patients who have previously undergone multiple ocular surgeries and therefore have very thin scleral tissue. In those patients, the graft material would be combined with Tenon duplication technique to prevent tube exposure. Our study showed no significant difference between the two techniques in terms of surgical success and complications. The finding that there was no statistically significant difference in the IOP-lowering effect of both techniques and in the incidence of HP in our study is a valuable new result.

There are over 1000 articles about AGV in the literature, yet there is no clear consensus on the failure criteria of AGV implantation. Although some authors consider the requirement of needling as a failure, there are some who consider the lack of regulation of IOP despite needling as a failure. For example, in the review of Riva et al.[29] and the study of Eibschitz-Tsimhoni et al.,[30] cases whose IOP could not be controlled despite medical treatment and 5-FU injection together with needling were considered unsuccessful. We do not consider needling as a failure, as all of the patients in our study who needed needling achieved the desired IOP values after needling and the values were found to be within normal ranges in their follow-up.

The limitations of our study include its retrospective nature, nonrandomized design, and follow-up loss at later time points. The selection bias due to the retrospective nature of the study could affect the reliability and validity. Although differences between the groups, especially in terms of gender, follow-up time, systemic disease, and glaucoma subtype, may affect the outcome of the study, we think that the acceptability of the study continues because there was no significant difference between the two groups. A possibility of overestimating surgical failure exists, as patients with more severe pathologies may continue to visit the ophthalmologist for longer periods. An underestimation of surgical failure is also possible due to the short follow-up time. The study’s strengths include the fact that all the operations were performed at a single hospital by two qualified surgeons. Comparison of the Tenon duplication technique and the dura mater covering technique also had not been done before.

In conclusion, the use of special allograft materials, which can prolong the operation time and increase the patient’s economic burden, may not be necessary in AGV implantation surgery, except in special cases.

Patient consent for publication

Not applicable.

Ethics approval

This study was approved by the ethics committee of Eskişehir Osmangazi University (approval ID: 04.10.2022/30), and the study complied with the tenets of the Declaration of Helsinki.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.