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EW GLAUCOMA 52 by Steven J. Gedde, M.D. Results from the Ahmed Baerveldt Comparison (ABC) Study A queous shunts (also known as tube shunts and glaucoma drainage im- plants) are being increas- ingly utilized in the surgical management of glaucoma as an alternative to trabeculectomy. Medicare claims data showed a 184% increase in aqueous shunt sur- gery and a concurrent 43% decrease in the number of trabeculectomies performed between 1995 and 2004. 1 Practice patterns in glaucoma sur- gery were evaluated with sequential surveys of the American Glaucoma Society membership, and selection of aqueous shunts as the preferred surgical approach in eight clinical scenarios increased from 17.5% in 1996 2 to 50.8% in 2008. 3 A growing concern about bleb-related compli- cations, including bleb infections and bleb dysesthesia, have con- tributed to the growing popularity of aqueous shunts. Commercially available aqueous shunts differ in design with regard to the size, shape, and material of the end plate. Shunts are also valved or non-valved, depending on whether a flow restrictor is present that limits aqueous flow if the IOP becomes too low. Glaucoma sur- geons have questioned the superior- ity of various aqueous shunts with respect to safety and efficacy. Several retrospective studies have failed to detect significant differences in sur- gical outcomes among different aqueous shunt types. 4-7 However, the conclusions of these studies are lim- ited by inherent biases of retrospec- tive investigations. The Ahmed Baerveldt Compari- son (ABC) Study is a large, multicenter, randomized clinical trial designed to compare the safety and efficacy of the Ahmed Glau- coma Valve (New World Medical, Rancho Cucamonga, Calif.) and the Baerveldt Glaucoma Implant (Abbott Medical Optics, Santa Ana, Calif.). 8 Patients with refractory glaucoma undergoing aqueous shunt surgery were randomly as- signed to placement of an Ahmed implant (model FP7) or Baerveldt implant (model 101-350). Outcome measures that were used to discrimi- nate the two treatment groups in- cluded visual acuity (VA), IOP, surgical complications, use of ad- junctive medical therapy, and failure (IOP>21 mm Hg or not reduced >20% from baseline, IOP<5 mm Hg, additional glaucoma surgery, re- moval of the shunt, or loss of light perception vision). A total of 276 patients were en- rolled in the ABC Study, including 143 in the Ahmed group and 133 in the Baerveldt group. Mean IOP was lower after Baerveldt placement after 1 year of follow-up (15.4 mm Hg Ahmed group vs. 13.2 mm Hg Baerveldt group, p=0.007), and use of adjunctive glaucoma medications was similar with both aqueous shunts (1.8 medications Ahmed group vs. 1.5 medications Baerveldt group, p=0.07). 9 The cumulative probability of failure at 1 year was not significantly different following Ahmed and Baerveldt implantation (16.4% Ahmed group vs. 14.0% Baerveldt group, p=0.52). More pa- tients who received a Baerveldt im- plant experienced early post-op complications during the first 3 months after surgery (43% Ahmed group vs. 58% Baerveldt group, p=0.016) and serious complications associated with reoperation and/or vision loss of two or more Snellen lines (20% Ahmed group vs. 34% Baerveldt group, p=0.014). No signif- icant difference in the rate of late post-op complications was observed between the two aqueous shunts (29% Ahmed group vs. 37% Baerveldt group, p=0.16). The lower IOP observed with the Baerveldt implant relative to the Ahmed implant is likely explained by the larger end plate, as larger sur- face area plates have been reported to produce greater pressure reduc- tion. 10 However, the greater efficacy of the Baerveldt implant in reducing IOP occurs at the expense of a higher rate of surgical complica- tions. The lower incidence of early post-op and serious complications after placement of the Ahmed im- plant compared with the Baerveldt implant probably relates to the valve mechanism that minimizes the risk of hypotony-related complications in the immediate post-op period. The ABC Study is a landmark clinical trial that has provided valu- able information to assist in surgical decision-making in similar patient groups. Other factors must be con- sidered when selecting a surgical procedure, including the surgeon's skill and experience with each aque- February 2011 June 2011 I n this month's inaugural glaucoma corner, the results of a critically im- portant study comparing the two most popular tube shunts are examined by Steve Gedde, M.D., a new member of the EyeWorld glaucoma editorial board. Dr. Gedde is one of the principle investigators of this study; he also has a leading role in the ongoing Tube Versus Trab (TVT) Study. The TVT Study has found that tube shunts may be superior to trabeculectomies both in efficacy and safety. The ABC Study compares the Ahmed Glaucoma Valve (New World Medical, Rancho Cucamonga, Calif.) to the Baerveldt Glaucoma Implant (Abbott Medical Optics, Santa Ana, Calif.). The results of these studies are essential in- formation for glaucoma surgeons, and we welcome Dr. Gedde's perspective. Reay Brown, M.D., glaucoma editor Baerveldt Glaucoma Implant (Abbott Medical Optics) continued on page 53 Glaucoma editor's corner of the world

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