Long-term Outcomes of Ahmed Glaucoma Valve Implantation in Refractory Glaucoma at Farabi Eye Hospital, Tehran, Iran.

PURPOSE: To describe long-term outcomes and complications of Ahmed glaucoma valve (AGV) implantation in subjects with refractory glaucoma at Farabi Eye Hospital, Tehran, Iran.
MATERIALS AND METHODS: This retrospective cohort study evaluated patient records of all subjects with refractory glaucoma who had undergone AGV implantation up to January 2013. The main outcome measure was the surgical success rate. Complete success was defined as intraocular pressure (IOP) <22 mmHg, without anti-glaucoma medications or additional surgery. Qualified success was IOP <22 mmHg regardless of number of anti-glaucoma medications. In all cases, loss of vision (no light perception) was considered an independent indicator of failure. Data were also collected on intraoperative and postoperative complications.
RESULTS: Twenty-eight eyes were included in the study. With a mean follow-up of 48.2 ± 31.7 months (median: 40.50 months; range: 3-124 months), the IOP decreased from a mean preoperative value of 30.8 ± 5.6 mmHg to 20.0 ± 6.4 mmHg at last visit. The number of medications decreased from 3.7 ± 0.4 preoperatively to 2.5 ± 1.1 postoperatively. Cumulative qualified success was achieved in 69% of eyes. Mean time to failure according to qualified success criteria was 92.3 ± 9.4 months. Postoperative complications were recorded in 16 (57.1%) eyes. The most common complication was focal endothelial corneal decompensation at the site of tube-cornea touch.
CONCLUSION: AGV implantation with adjunctive topical anti-glaucoma drops controlled IOP in approximately 70% of eyes with refractory glaucoma with a median of 40.5 months of follow-up. However, complication rates were higher.

INTRODUCTION

Globally, glaucoma is the leading cause of irreversible blindness, and this is especially relevant to complicated, refractory cases of glaucoma.1 Glaucoma drainage devices (GDD) are frequently used for the management of refractory glaucoma cases, and as a secondary choice following failure of other surgeries. Additionally, several studies have reported favorable results with GDD implantation as the primary surgical option in glaucoma patients.234

The Ahmed glaucoma valve (AGV; New World Medical, Inc., Rancho Cucamonga, California, USA) was introduced into the market at 1993 and has a built-in silicone venturi valve to restrict aqueous outflow and prevent postoperative hypotony.5 It is used in refractory glaucoma cases both as a primary surgical choice and after the failure of conventional filtering surgery.

Several reports exist on success rate of AGV in different situations and races.46789 However, reports are rare on long-term outcomes of the device from the Middle East. In the current study, we evaluated the outcomes of AGV implantation in refractory glaucoma cases in a major Tertiary Eye Hospital in Iran.

MATERIALS AND METHODS

This retrospective cohort study evaluated the medical records of patients with refractory glaucoma who underwent AGV implantation at Farabi Eye Hospital, Tehran, Iran. The chart review included all consecutive cases with refractory glaucoma, unresponsive to medical and conventional surgical intervention, who underwent AGV implantation by one surgeon (Prof. Heidar Amini) between July 2002 and April 2004. We selected this period to evaluate the long-term result of the cases that is the fate of the procedure over a 10-year period. The chart review was performed in 2013. Patients with previous drainage device implantation were excluded from the study. As the hospital serves both primary and referral patients, some of the operated patients are followed-up by the referring physician and have follow-up data were missing after the 1st postoperative week. These cases were excluded from this study. Preoperative data were collected on patient age, gender, intraocular pressure (IOP) measured by a calibrated Goldmann applanation tonometer, number of anti-glaucoma medications, best-corrected visual acuity using a tumbling E-chart, and cup-to-disk ratio. Surgical data were collected including any intraoperative complications along with other intraoperative findings and site of AGV implantation. Postoperatively, data were collected on IOP, the number of medications and complications. All surgical and clinic records in the hospital were hard copies and were reviewed case by case for this study.

Complete success was defined as IOP <22 mmHg, without anti-glaucoma medications or need for additional surgery. IOP <22 mmHg regardless of the number of anti-glaucoma medications was classified as qualified success. IOP ≥22 mmHg with maximal, tolerable medications, IOP ≤5 mmHg, need for additional surgical intervention, loss of light perception, or phthisis bulbi was considered a surgical failure.

Surgical technique

One experienced surgeon (HA) performed all surgeries. Briefly, under monitored anesthetic care along with topical and subconjunctival anesthesia for adult patients and general anesthesia for pediatric subjects; a clear corneal traction suture was placed parallel to limbus and a limbal based superotemporal or superonasal peritomy was performed. The AGV was primed with balanced salt solution, and its plate was fixed to sclera at least 10 mm posterior to the surgical limbus with two nylon 8-0 sutures. The tube was trimmed and inserted into the anterior chamber in a plane parallel to iris and as far from corneal endothelium as possible. A scleral patch graft from banked donor sclera was placed over the tube, and water tight closure of Tenon's and conjunctiva was performed with running vicryl 8-0 sutures. At the conclusion of surgery, subconjunctival cefazoline, and betamethasone were administered.

Statistical analysis

The main outcome measure was surgical success rate. Kaplan-Meier survival analysis was performed to evaluate success rate over the study period. Furthermore, repeated measure analysis of variance (ANOVA) along with Bonferroni adjustment was performed to evaluate IOP and medication changes over time. All statistical analyses were performed using SPSS software (IBM Corp., New York, NY, USA). A P < 0.05 was considered as statistically significant.

RESULTS

Twenty-eight eyes of 28 patients were eligible and included. The mean age was 44.3 ± 22.3 years (median: 44.00 years; range: 7–75 years). Fifteen patients were male (53.5%), and all included patients were Caucasians and Iranians. The mean follow-up time was 48.2 ± 31.7 months (median: 40.5; range: 3–124 months); 92.8% had at least 12 months follow-up and 78.5% of participants had 24 months follow-up. Pseudophakic glaucoma was the most common type of glaucoma (13 eyes; 46.4%). Demographic and preoperative clinical data of the participants are summarized in Table 1.

Table 1

Demographic data and preoperative characteristics of eyes that underwent Ahmed glaucoma valve implantation in this study

Mean preoperative IOP was 30.8 ± 5.6 mmHg (range: 23.0–50.0 mmHg) with 3.7 ± 0.4 medications (range: 3–4 medications). All cases had IOP >22 mmHg despite using IOP lowering medications. Mean postoperative IOP decreased to 20.0 ± 6.4 mmHg (range: 15.0–35.0 mmHg) with a mean of 2.5 ± 1.1 (range: 0–4) medications. Table 2 represents the IOP over the postoperative visits. The IOP, differed statistically significantly at different times when analyzed with ANOVA using Bonferroni adjustment. However, using Tukey's post-hoc test, a statistically significant difference was observed only for comparison between preoperative and postoperative IOPs at different times (P < 0.0001), and there was no statistically significant difference between IOP measurements comparing different postoperative visits.

Table 2

Intraocular pressure and number of medications preoperatively and postoperatively

In life-table survival analysis and based on the predefined success criteria, qualified success was achieved in 69% of subjects at the end of 120 months of follow-up. The mean ± standard error of mean time to failure according to complete and qualified success criteria was 51.6 ± 6.8 months and 92.3 ± 9.4 months, respectively [Figure 1].

Figure 1

Survival curve of complete success following Ahmed glaucoma valve implantation in 28 eyes with refractory glaucoma (a) complete success, (b) qualified success

On average, visual acuity decreased by one Snellen line at the last postoperative visit. Mean preoperative visual acuity was 0.62 ± 0.43 logarithm of the minimum angle of resolution units and statistically significantly decreased to 0.76 ± 0.49 at last follow-up visit (P = 0.007). The visual acuity remained unchanged in 12 (42.9%) eyes, improved in 6 (21.4%) eyes, and decreased in 10 (35.7%) eyes (P < 0.0001).

No major intraoperative complications were recorded. Postoperative complications occurred in 16 (57.1%) eyes [Table 3]. The most common complication was focal endothelial corneal decompensation due to tube-cornea touch in 3 (10.7%) eyes. This complication was managed with surgical tube revision. Two aphakic eyes had vitreous incarceration in the tube orifice and were managed with neodymium-doped/yttrium aluminum garnet vitreolysis. AGV tube was extruded in two cases, which were managed with scleral patch graft and conjunctival advancement.

Table 3

Postoperative surgical complications following Ahmed glaucoma valve implantation in 28 Iranian eyes with refractory glaucoma

Qualified success was achieved in 77.8%, 69.2%, and 66.7% of phakic, pseudophakic and aphakic eyes, respectively (P = 0.871).

Table 4 compares the results of the current study with the results of previously published articles.

Table 4

Summary of previous published study on surgical outcome of glaucoma drainage devices along with the result of current study

DISCUSSION

In the current study, we retrospectively reviewed the results of AGV implantation in Iranian patients with refractory glaucoma. In this series of 28 patients with a median follow-up time of 40.5 months, 69% of eyes achieved qualified success. However, various complications were encountered in almost 57% of cases during follow-up.

Surgical success rates for glaucoma shunting procedures vary in published studies from 20%32 to 98%.20 However, because of differences in the study population, type of implants, and the duration of follow-up, the results are not directly comparable to our study. Hence, it is tenous at best to make a globally valid conclusion about the efficacy of the procedure for the refractory glaucoma cases. The majority of the current body of literature regarding the success of drainage devices is from the developed countries, whereas refractory glaucoma seems to be more prevalent and disabling in developing and undeveloped countries.33 The current study focused on the long-term success of AGV shunting procedure in refractory glaucoma cases in Iran.

Table 4 presents the outcomes of previous studies on tube shunt implantation including our study. The differences on types of races of the study population could explain the variations in success rate between studies. Interestingly, a large multicenter study by Gedde et al.17 (tube vs. trabeculectomy study [TVT]) had compared outcomes of primary shunting procedure, using 350 mm2 Baerveldt glaucoma implant in 107 eyes, and trabeculectomy with mitomycin C in 105 eyes. The cumulative probability of failure for tube shunt (vs. trabeculectomy) during 1st year, first 3 years, and first 5 years of follow-up was, 3.9% (vs. 13.5%), 15.1% (vs. 30.7%), and 29.8% (vs. 46.9%), respectively.23435 They17 concluded that tube shunts had a higher success rate than trabeculectomy in their cohort of patients. The cumulative probability of failure in the current study at 1-year, 3-year, and 5-year follow-up was 14%, 31%, and 31%, respectively. These rates are higher than the TVT study.17 Syed et al.26 reported similar surgical outcomes for the Ahmed and Baerveldt implants, and we believed that the observed differences are because we included eyes with failed previous incisional surgeries in our study. Souza et al.6 retrospectively evaluated 78 eyes with AGV implant and proposed that prior glaucoma surgery could increase the risk of failure of AGV implantation by more than three-fold.

In the current study, postoperative complications occurred in 57.1% of eyes. We implanted silicon type AGV (AGV FP7) in our patients that may be associated with a higher complication rate.36 However, there was no major tube-related visual loss in our patients, and our complication rate is comparable to previous studies [Table 4].

Limitations of this study include the retrospective design and the small sample-size. Another drawback was our inclusion of only subjects with previously failed incisional surgeries and refractory glaucoma in the study. Additionally, the study population was heterogeneous in terms of the type of glaucoma and duration of follow-up. Farabi Eye Hospital is the largest Referral Eye Hospital in Iran, and many patients went for further management to the referring ophthalmologist after a few postoperative visits. Hence, we had a high rate of patient dropout. However, our study has the largest follow-up of AGV implantation in the region.

CONCLUSIONS

We believed that AGV implantation could have an acceptable success rate in patients with refractory glaucoma and failed previous incisional glaucoma surgery in patients in the Middle East. However, to achieve adequate IOP control, topical anti-glaucoma medications should be continued postoperatively in most subjects. A further implication of the current study is the need for periodic, long-term follow-up for proper management of failures or complications. After the 1st postoperative month, we suggest follow-up visits every 3 months in the 1st year, then every 6 months over the next 4 years, and annually thereafter. However, this recommendation should be further validated and should be tailored according to clinical judgments on many factors including but not limited to the severity of glaucomatous damage, level of IOP, general health of patients, and life expectancy.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.