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To compare the surgical outcomes of the two different methods used for Ahmed Glaucoma Valve (AGV) implantation between the donor scleral graft method and the partial-thickness scleral flap method.
We retrospectively reviewed medical records of 28 eyes of 26 patients diagnosed as neovascular glaucoma followed by AGV implantation. Based on the surgical method, the included eyes were divided into two groups. In the graft group (n = 18), the drainage tube was inserted into the anterior chamber, and then covered with preserved donor sclera. In the flap group (n = 10), the drainage tube was inserted under the partial-thickness scleral flap, and then covered with the flap. We compared the postoperative intraocular pressure (IOP), surgical success rates, and postoperative complications between the two groups.
Postoperative IOP was not significantly different between the two groups (
In AGV surgery for neovascular glaucoma, the scleral graft method may be associated with relatively less complication about tube migration than the scleral flap method. The surgical results, however, were not statistically different.
Various glaucoma drainage devices (GDDs) have been used for the treatment of refractory glaucomas, such as neovascular glaucoma (NVG), and the performance of GDDs can be significantly different among each individual product [
To the best of our knowledge, there have been few studies that compared the outcomes of two different surgical techniques used for AGV implantation. The purpose of this study is to compare the surgical outcomes between the scleral graft method and partial thickness scleral flap method in AGV implantation.
We retrospectively reviewed the medical records of patients diagnosed as NVG who underwent AGV implantation at the Eulji General Hospital in Seoul, Korea between January 2001 and December 2007. The institutional review board of Eulji Medical Center approved the study protocol before patient enrollment.
Inclusion criteria were as follows: 1) age between 20 to 85 years, 2) inadequately controlled NVG due to proliferative diabetic retinopathy (PDR) or central retinal vein occlusion (CRVO), and 3) an IOP above 22 mmHg in spite of maximum tolerated medical therapy. Patients who had no light perception preoperatively or who underwent the AGV implantation for other secondary glaucomas were excluded from this study.
All of the participants had follow-up periods of six months or longer after AGV implantation. Preoperative data included age, sex, implanted AGV model, preoperative IOP, and the number of topical IOP depressants. The eyes were divided into two groups according to the surgical methods covering the silicone drainage tube of AGV. In the graft group (n = 18), the drainage tube was inserted into the anterior chamber, and then covered with preserved donor sclera. In the flap group (n = 10), the drainage tube was inserted under the partial-thickness scleral flap, and then covered with the flap.
The selection of the surgical method for each patient depended on the donor sclera's availability when the operation was planned. That is, when the donor sclera was available, we performed the AGV surgery using the donor sclera graft method; otherwise we performed the surgery using the scleral flap method. The donor sclera used in AGV implantation was obtained from patients diagnosed with traumatic eyeball rupture at our hospital. The remaining cornea, lens, and uvea (iris, ciliary body, and choroid) of the enucleated eyeballs were clearly removed with scissors and blades. Only the sclera was preserved in 99.9% ethyl alcohol at a refrigerator temperature at 4℃.
The donor had no abnormal results on laboratory tests for infectious diseases such as hepatitis, acquired immunodeficiency syndrome, and syphilis. All patients were operated on by one surgeon (JSP). The S2 model had been used before 2004, while the FP7 model replaced the S2 model since 2004.
All patients underwent AGV implantation under retrobulbar anesthesia. A fornix-based conjunctival-Tenon's capsule flap was created in the superotemporal or superonasal quadrant, and blunt dissection was performed between Tenon's and the episclera for AGV implantation beyond the equator of the globe. The tip of the drainage tube was then irrigated with a 26-gauge blunt cannula containing BSS (Alcon Laboratories Inc., Fort Worth, TX, USA) for priming. The valved plate body was then inserted posteriorly into the sub-Tenon's space and sutured to the sclera with 9-0 nylon sutures through the anterior positional holes of the valved plate body, 8 mm posterior to the limbus. The tip of the drainage tube was then cut and beveled up in order to extend by 2 to 3 mm into the anterior chamber. A paracentesis was then made at the limbus, and a small amount of viscoelastic material was injected into the anterior chamber. In the graft group, the anterior chamber was then entered through the limbal area, approximately 0.5 to 1 mm posterior to the limbus, using a 23-gauge needle. The drainage tube was then inserted into the anterior chamber parallel to the iris plane and was secured to the sclera with 10-0 nylon sutures. The preserved donor sclera was then rehydrated in a BSS bath and trimmed to approximately 4 × 7 mm in size. The drainage tube was then covered with preserved donor sclera to avoid potential complications such as tube erosion, and the donor scleral graft was sutured to the underlying sclera at each corner with 10-0 nylon sutures. The conjunctiva and Tenon's capsule were then sutured back to the original position using 8-0 vicryl sutures.
In the flap group, a half-thickness, rectangular, 4 × 4 mm and limbal-based scleral flap was created. The valved plate body was then inserted posteriorly into the sub-Tenon's space and sutured to the sclera with 9-0 nylon sutures through the anterior positional holes of the valved plate body, 8 mm posterior to the limbus. The anterior chamber was then entered with a 23-gauge needle under the scleral flap, then the drainage tube was inserted into the anterior chamber and was secured to the sclera with 10-0 nylon sutures. The scleral flap over the drainage tube was re-attached to the sclera and sutured with 10-0 nylon sutures.
Complete surgical success is defined as 6 mmHg ≤ IOP ≤ 21 mmHg without IOP-lowering medication, additional glaucoma surgery, nor loss of light perception during the follow-up period. Qualified success is defined as 6 mmHg ≤ IOP ≤ 21 mmHg with supplemental medication, but without loss of light perception. Mean success periods are defined as a time to maintain "qualified success" or "complete success" from an initial visit, and those were compared to each other by log rank test. Failure is defined as follows: 1) constant hypotony below 6 mmHg, 2) IOP > 21 mmHg despite of supplemental medication at least three times consecutively, 3) further glaucoma surgical intervention or recommendation thereof, or 4) loss of light perception. Further surgical intervention for glaucoma is defined as additional glaucoma surgery that requires a return to the operating room, such as placement of another tube shunt, tube exchange, and tube removal, etc. Intracameral injection of air or viscoelastics for maintaining the anterior chamber was excluded from this category and would not be recorded as evidence of failure until three months postoperative.
We collected data such as IOP, and postoperative complications at one day, one week, two weeks, one month, three months, six months, and one year or more postoperatively until the last visit. IOP was measured with a Goldmann applanation tonometer. We prescribed topical IOP-depressants (maximally, three eye drops) for the patients with an IOP more than 21 mmHg during follow-up periods.
Statistical analysis was done by SPSS ver. 17.0 (SPSS Inc., Chicago, IL, USA). The preoperative data for the two groups were compared using the Mann-Whitney
This study investigated 28 eyes (18 eyes in the graft group and ten eyes in the flap group).
The mean IOP values in the graft group versus the flap group were as follows (
Six months postoperative, complete and qualified success rates were 22.2% (4 / 18) and 72.2% (13 / 18) in the graft group, and 10.0% (1 / 10) and 80.0% (8 / 10) in the flap group, respectively. At postoperative one year, the complete and qualified success rates were 22.2% (4 / 18) and 55.6% (10 / 18) in the graft group, and 10.0% (1 / 10) and 70.0% (7 / 10) in the flap group, respectively (
The aim of the present study was to compare the surgical outcomes of the two methods for AGV implantation. In our study, the graft group and flap group did not show significant differences in terms of postoperative IOP and the mean success period. At about six months postoperative, we observed three cases of tube obstruction and subsequent temporary elevation of IOP in the flap group. Such factors as a small sample size (n = 10) and an abrupt change of individual IOP might have affected the overall mean IOP, and thereby resulted in significant deviation from the normal. The overall success rate of AGV implantation varies among different types of glaucoma, ranging from 63% to 100% at one year of follow-up [
All cases, which had shallow anterior chamber or early hypotony in the graft group, were spontaneously resolved in the postoperative one week. Two eyes, which had persistent shallow anterior chamber or hypotony in the flap group, were treated with intracameral injection of viscoelastics or air. We observed no tube migration in the graft group, but three eyes (30.0%) demonstrated tube migration in the flap group, which was statistically significant (
However, we need to consider the potential problems when a preserved donor sclera is used for covering the drainage tube. Donor scleral grafts may transmit several infectious diseases. Seiff et al. [
Although we used preserved donor sclera for covering the drainage tube, we were also able to use Tutoplast to cover the drainage tube. Tutoplast is more readily available and easier to handle because of its uniform quality and size. In addition, Tutoplast has been sterilized through gamma-irradiation and chemical treatment [
We concluded that the frequency of tube migration was significantly higher in the flap group than the graft group. However, postoperative IOP values and surgical success rates were not significantly different between the two methods. This study has some limitation due to the lack of long-term follow-up and small case number. Further studies with longer follow-up and larger case number will be needed to assure our conclusion.
No potential conflict of interest relevant to this article was reported.
The baseline and postoperative intraocular pressure (IOP) measurements in the graft group and flap group. Only at six months postoperatively did the graft group have a significantly lower mean IOP compared to the flap group (indicated by an asterisk,
The cumulative survival graph was determined by the Kaplan-Meier method, and the success rate was compared using the log rank test. The cumulative success rates were 94.4% versus 90.0% at six months and 77.8% versus 80.0% at one year in the graft and flap groups, respectively. The success rates were not significantly different (
Baseline characteristics in the graft group and flap group
Values are presented as mean ± SD or number (%).
IOP = intraocular pressure; NVG = neovascular glaucoma; DM = diabetes mellitus; CRVO = central retinal vein occlusion; AGV = Ahmed Glaucoma Valve.
*Mann-Whitney
The surgical results of both group at postoperative six months and one year
*Analyzed by Fisher's exact test.
Postoperative complications in the graft group and flap group
Values are presented as number (%).
*Aanalyzed by Pearson chi-square test; †Analyzed by Fisher's exact test; ‡Indicates hypotony occurring within the first postoperative month.