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Glaucoma drainage devices: Location, location, location
With glaucoma drainage devices gaining in popularity, the implantation technique must be tweaked to achieve the best results with the fewest complications.
Take-home message: With glaucoma drainage devices gaining in popularity, the implantation technique must be tweaked to achieve the best results with the fewest complications.
By Lynda Charters; Reviewed by Herbert P. Fechter III, MD
Augusta, GA-Glaucoma implants seem to be gaining in popularity among glaucoma surgeons over trabeculectomy because of the incidence of fewer complications, noted one physician. However, as with all medical devices, the implantation of glaucoma shunts-such as the Baerveldt Glaucoma Implant (Abbott Medical Optics Inc. [AMO]) and Ahmed Glaucoma Valve (New World Medical)-may have its fair share of complications and adverse events, explained Herbert P. Fechter III, MD.
Despite this, however, he noted that the rates of implantations of the drainage devices have increased over the past decade, likely because of the outcomes of two major trials, the Tube vs. Trabeculectomy Study (Gedde et al., Am J Ophthalmol 2012;153:789-803) and the Ahmed versus Baerveldt Study (Christakis et al. Ophthalmology 2013:120: 2232-2240).
Dr. Fechter, who is in private practice in Augusta, GA, pointed out that with adjustments in Medicare coding, i.e., bundling of aqueous shunt surgery with scleral reinforcement with a graft, glaucoma surgeons will be taking a closer look at their glaucoma surgery techniques and selectively not using patch grafts in the future.
“I have experienced devastating complications such as phthisis bulbi and endophthalmitis and unfortunate complications such as suprachoroidal hemorrhages and retinal detachments. Uveitis can be particularly challenging for glaucoma surgeons because of excessive inflammation that leads to posterior synechiae, iris bombe, and seriously elevated or decreased IOPs,” he said. “In addition, diplopia can develop in about 5% of patients as the result of exuberant blebs, a thick Tenon’s capsule, or an improper plate position.”
Hypotony, a flat anterior chamber, and serous choroidal effusions tend to occur together, he commented. “The postoperative hypotonous eye, with a flat anterior chamber and the tube pressing against the cornea, can be due to several reasons: perhaps because the 7-0 suture ligature was not tight enough, the fenestrations were too exuberant, the sclerotomy site was too large, or the creation of an inadvertent cyclodialysis cleft,” he said.
He offered an example of a patient whose tube opened five weeks after surgery and whose pressure rapidly dropped from 40 mm Hg to single digits, leading to hypotony. “Serous choroidal effusions can develop and, without resolution, hypotony maculopathy may ensue,” Dr. Fechter said.
In these eyes, he uses a viscoelastic device to raise IOP temporarily and deepen the shallow anterior chamber.
Dr. Fechter raised the question about whether proper tube position can decrease the risk of complications, to include corneal endothelial compromise and tube erosion.
He offered ways to improve the tube insertion technique promoted on both the AMO and the New World Medical websites, which demonstrate the tube being routed directly into the anterior chamber through a short scleral tunnel. Dr. Fechter believes that using a long scleral tunnel and directing the tube more superiorly greatly reduces the risk of tube exposure.
His modified technique is demonstrated in three YouTube videos:
Top complications
“These top five complications are all related to ideal tube placement. If the patch graft is removed from the equation, I believe these five complications are going to be important,” Dr. Fechter said.
Modifying the tube position may be advantageous, he said. He likes to make a longer scleral tunnel and route the tube more superiorly than demonstrated on the manufacturer’s web site. The longer scleral tunnel may make the patch grafts unnecessary. He shared that Felix Gill Carrasco, MD, in Mexico City reported 10 years ago that he used this approach in hundreds of cases in which Ahmed devices were implanted without a patch graft and there was no increase in the rate of tube exposure.
A complication that may occur more frequently when creating the long tunnel is postoperative mild hyphema. In contrast to directing the tube straight into the cornea at the limbus, this recommended approach goes more posteriorly and may nick the blood vessels supplying the iris root and ciliary body inadvertently.
“More hyphemas can be expected postoperatively, but they tend to resolve spontaneously within several weeks with no extra medications,” he said.
Another of the top five complications is tube blockage by iris or vitreous.
“If vitreous migrates toward the tube tip, a vitrectomy is needed to obtain the best results,” Dr. Fechter explained.
He uses an anterior bevel when the tube is directed in front of the iris and a posterior bevel when the tube is behind the iris to avoid tube occlusion.
“I like entering posterior to Schwalbe’s line to reduce corneal complications,” he commented. If the tube is too long or positioned too far anteriorly, the corneal endothelium can be damaged, which leads to bullous keratopathy with endothelial cell failure. When the tube is positioned posterior to Schwalbe’s line, the rate of endothelial cell loss will be less, he advised.
Dr. Fechter also advised examining the anterior chamber angle for peripheral synechiae preoperatively to determine the best location to direct the tube. If there is a large iridectomy, the tube can be directed through it and placed more posteriorly, away from the endothelial cells. In pseudophakic patients, the tube can be positioned behind the iris.
“Tube erosion tends to occur where the lid margin crosses the sclera. Routing the tube more superiorly and utilizing a long scleral tunnel may help avoid erosions,” he said.
The technique he uses involves entering the eye at the 12 o’clock position and creating a tunnel about 4 mm long. To do this, he uses a 23-gauge needle, routes it into the anterior chamber parallel to the iris, and then directs the tube through the tunnel.
“By doing this, friction from an elevated tube is greatly reduced and the patch graft can possibly be eliminated,” he emphasized.
Shunts remain an excellent option
Despite the complications, Dr. Fechter thinks that tube shunts remain an excellent option for patients with moderate to severe glaucoma.
“We want our patients with glaucoma drainage devices to have comfortable eyes, with good vision and low IOP. With some technique modifications, we can reduce the risk of tube exposure, tube occlusion and corneal decompensation. As glaucoma surgeons, we constantly strive to improve our surgical techniques to provide our patients with the most effective, efficient and safest surgery,” he concluded.
Herbert P. Fechter III, MD
Dr. Fechter has no financial interest in any aspect of this report.
