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Abstract and Introduction
Abstract
Purpose To compare the safety and intraocular pressure (IOP) lowering efficacy of initial glaucoma drainage device (GDD) implantation performed at the superior versus inferior limbus.
Methods A retrospective chart review was conducted to identify patients with glaucoma who had undergone initial Baerveldt GDD surgery at the inferior limbus for uncontrolled IOP. All eyes of patients had a minimum of 6 months of postoperative follow-up. These eyes were frequency-matched to eyes with initial Baerveldt GDD implantation performed at the superior limbus, within 5 years of age and 6 months of follow-up. Baseline demographic and clinical information, as well as preoperative and postoperative IOP, visual acuity, and number of antiglaucoma medications were extracted. Failure was defined as IOP>21 mm Hg or not reduced by 20% below baseline on 2 consecutive follow-up visits after 3 months, IOP≤5 mm Hg on 2 consecutive follow-up visits after 3 months, reoperation for glaucoma, or loss of light perception vision. Statistical methods consisted of Student t tests, χ test, and Kaplan-Meier time to failure analysis.
Results Fifty eyes (17 inferior, 33 superior) of 43 patients were enrolled. Mean postoperative follow-up in both groups were similar (mean 26.2±15.2 mo for inferior and 23.9±10.43 mo for superior, P=0.54). Trabeculectomy had been performed previously in 8/17 (47%) and 11/33 (33%) eyes (P=0.34) with inferior and superior implants, respectively. Mean preoperative IOP (mm Hg) in the superior group (26±11) was significantly higher (P=0.02) when compared with the inferior group (21±7). Success rates were similar (P>0.05) between the inferior and superior GDD groups during the study period, with 64.7% and 75.8% classified as successful at 1-year of follow-up and 43.1% and 65.7% at 2 years of follow-up, respectively. There was no difference in cumulative proportions of eyes failing between the groups (P=0.20, log-rank test). The mean postoperative IOP and number of antiglaucoma medications were similar (all P>0.05) in both groups during the first 2 years of postoperative follow-up. The frequency and types of postoperative complications in both the groups were similar. The 36-month cumulative reoperation rates for IOP control were 33.8% and 9.1%, respectively, in the inferior and superior GDD groups (P=0.04 log-rank test).
Conclusions No differences were observed in the overall success rates of initial GDD implantation performed at the superior and inferior limbus in this cohort. However, inferior GDD implantation was associated with a greater incidence of reoperation for IOP control.
Introduction
Elevated intraocular pressure (IOP) is the most important and only modifiable risk factor for the development and progression of glaucomatous optic neuropathy. Current therapies are therefore directed towards lowering IOP. Glaucoma surgery is indicated when the medical therapy and appropriate laser treatment do not provide adequate IOP reduction. Since their introduction in 1969, glaucoma drainage devices (GDDs) have been incorporated in the surgical management of patients with uncontrolled IOP. GDDs create an alternate aqueous pathway from the anterior chamber by channeling aqueous out of the eye through a tube to a subconjunctival bleb or to the suprachoroidal space. This tube is usually connected to an equatorial plate under the conjunctiva.
Tube shunts have traditionally been reserved for refractory glaucomas at high risk of failure with trabeculectomy. A growing experience with these devices has prompted their use in the eyes with lesser risk of trabeculectomy failure. Improvements in the material design and surgical techniques for performing GDD implant surgery have led to increased utilization in the recent years. Data from the United States Medicare database for glaucoma procedures performed between 1995 and 2004 demonstrate a 184% increase in the number of aqueous shunt procedures.
GDDs differ in terms of implant material, size, and design features, including the presence or absence of a valve that limits aqueous flow through the device if the IOP becomes too low. Two commonly utilized devices include the Baerveldt Glaucoma Implant (BGI) (Abbott Medical Optics Inc., Abbott Park, IL) and the Ahmed Glaucoma ValveTM (AGV) (New World Medical Inc., Rancho Cucamongo, CA). A recent randomized controlled study comparing the BGI and the AGV reported that the average IOP 1-year postoperatively was slightly higher in patients who received an AGV, however, this group experienced fewer early and serious postoperative complications. GDD surgery is commonly performed at the superotemporal limbus and may offer advantages including greater intraoperative exposure for the surgeon, greater postoperative coverage of the patch graft by the upper eyelid, and relatively increased orbital volume in that area to accommodate a bleb over the plate. GDD placement at the inferior limbus may be required in the eyes with extensive superior conjunctival scarring, intraocular silicone oil, or poor exposure.
Limited data exist comparing the relationship between the orbital location of GDD implantation and surgical success. Rachmiel et al reported a similar IOP control in the eyes after superior AGV implantation when compared with the inferior placement. We hypothesized that the relatively larger surface area of the BGI (350 mm) when compared with the AGV (184 mm) may predispose to a higher rate of complications when performed at the inferior limbus, owing in part to the reduced space in the inferior conjunctival fornix when compared with the superior fornix. We conducted the present study to compare the safety and the IOP lowering efficacy of initial BGI implantation performed at the superior versus inferior limbus in patients with glaucoma with uncontrolled IOP.
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