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Implantation of a miniature glaucoma device (Ex-PRESS R-50, Optonol) under a scleral flap is a modification of trabeculectomy that appears to provide similar IOP-lowering efficacy but with fewer complications.
Pittsburgh-Although the search for a better alternative to trabeculectomy continues, experience with implantation of a miniature glaucoma device (Ex-PRESS R-50, Optonol) under a scleral flap indicates that this procedure is fulfilling the important goal of achieving IOP lowering with a more favorable safety profile, said Garry P. Condon, MD.
"Placement of the miniature glaucoma implant under a scleral flap is really a modification of trabeculectomy. It does not eliminate a bleb, and the art of surgery and meticulous attention to detail are still mandatory" said Dr. Condon, associate professor and director, glaucoma division, Department of Ophthalmology, Allegheny General Hospital, Pittsburgh. "However, it is minimally penetrating surgery that causes less tissue trauma and appears to offer more stable early postoperative outflow and anterior chamber depth along with reduced risks of hyphema and choroidal effusion. When it comes to reducing complications of glaucoma surgery, any step forward is a step in the right direction."
The implant is a small steel device that originally was inserted under the conjunctiva. That procedure was associated with complications, particularly device exposure due to conjunctiva erosion, and was abandoned for several years until Dahan and Carmichael introduced the scleral flap-based procedure performed at the limbus. Their technique was published in a paper in 2005, and the procedure has gained wider attention based on reports from Netland and colleagues at the University of Tennessee.
The implant is pre-loaded and introduced through a 27-gauge needle track. With this small entry, the anterior chamber remains perfectly stable without the need for viscoelastic, Dr. Condon said.
"This is not nonpenetrating surgery, but with just a 27-gauge hole, this is minimally penetrating surgery," Dr. Condon said.
He recommended using adjustable slip knots to achieve a snug scleral flap closure while allowing intraoperative adjustment of aqueous egress. A watertight conjunctival closure also is imperative, he said.
In a retrospective study reported in 2007, Netland and colleagues revealed outcomes through 15 months of follow-up for 50 eyes with the miniature glaucoma device implanted under a scleral flap and 50 eyes that underwent standard trabeculectomy. During the first 3 to 5 days after surgery and at subsequent visits through 3 months, mean IOP was significantly lower in the patients who underwent trabeculectomy compared with the implant group. No significant between-group differences in mean IOP were seen thereafter, however, nor were significant between-group differences seen in a survival curve analysis of success rates.
Importantly, the incidence of early hypotony was 32% in the trabeculectomy group compared with only 4% in the miniature implant group. Choroidal effusion also was much less common with the implant compared with trabeculectomy: 8% versus 38%. The between-group differences in rates for both complications were statistically significant.
"I believe it is this information and the propagation of this approach that changed the way the miniature implant is being used in this country. Recent data showing an increase in tube surgery reflect primarily usage of this device. While 2,275 of these miniature implant procedures were performed in 2006, that number increased dramatically to 5,600 in 2007," said Dr. Condon.
He reported that his personal experience parallels the outcomes reported by Netland et al. In analyses of data for 41 eyes with the miniature implant and 32 eyes with trabeculectomy, mean IOP was a little lower in the implant group at 3 months, although the difference was not statistically significant. Patients with the implant had fewer complications, however, he said.
"There were no eyes with hyphema, choroidal effusion or shallow anterior chamber in the implant group, while each of these complications occurred in two or three eyes after trabeculectomy," Dr. Condon reported.
Compared with trabeculectomy
Compared with standard trabeculectomy, the implant procedure also is associated with less tendency for blood to be directed back into the opening and into the anterior chamber, and it may minimize scleral fibrosis because the metal flange of the implant would reduce the surface area available for scarring.
Dr. Condon observed that the implant surgery does not eliminate concerns about bleb-related complications. Late migration of the device is a potential concern but has not been seen so far. Also, compared with standard trabeculectomy, the implant procedure has a higher cost. Angle-closure glaucoma is a relative contraindication, he said.