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Second glaucoma drainage implants significantly reduce IOP, medication use
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PHILADELPHIA — Second glaucoma drainage implants can markedly reduce IOP and medication use but had a high failure rate, according to a study presented here.
“The majority of eyes can still achieve adequate IOP control with fewer agents, avoiding cyclodestructive procedures,” Wanda D. Hu, MD, said at the Wills Eye Annual Conference.
Hu said that tube shunt surgery has become more popular in recent years.
“Trabeculectomy has always been the gold standard for glaucoma surgery … but the rates of tube shunt surgery have been going up in the past decade significantly, especially with publication of the Tube Versus Trabeculectomy Study, which showed that Baerveldt tube shunts have about the same IOP lowering as trabeculectomy,” Hu said.
However, the TVT Study showed that about 30% of Baerveldt implants (Abbott Medical Optics) failed at 5 years, she said.
“The reason why a lot of these tube shunts failed is because there was a lot of fibrosis around the plate, which [impeded] the aqueous flow out of the anterior chamber,” Hu said.
In the event of tube shunt failure, strategies include needling the fibrotic bleb around the plate, excising an encapsulated bleb, performing endoscopic cyclophotocoagulation (ECP) or transscleral cyclophotocoagulation, and inserting a second tube shunt, Hu said.
Patients and procedures
The retrospective study included 65 eyes of 63 patients. Minimum follow-up was 3 months, and average follow-up was about 2 years.
Primary outcome measures were IOP reduction and failure rates. Secondary outcome measures were postoperative medication use, reoperation rates and complications.
A majority of patients had primary open-angle glaucoma, and all patients had prior tube shunt insertion. About 25% of patients had neovascular or uveitic glaucoma, and 15% had chronic angle-closure glaucoma.
The average interval from primary tube shunt insertion to secondary insertion was 32 months.
“All these patients had at least one glaucoma surgery because they all had a tube shunt,” Hu said. “But most of them had two to four prior glaucoma surgeries. Those included trabeculectomies, bleb needling and ECP. … A lot of these patients had sick eyes. A lot of them had penetrating keratoplasties, prior vitrectomies and a conjunctiva that was not very healthy.”
Second implants were primarily Ahmed FP7 glaucoma valves (New World Medical) and Baerveldt 250 implants, Hu said.
Of 30 eyes that received second inferotemporal tube shunts, 26 received Ahmed valves.
Of 23 eyes that received second tube shunts inserted in the inferonasal quadrant, 18 received Baerveldt implants.
Success was defined as IOP between 5 mm Hg and 22 mm Hg after 3 months and a 25% IOP reduction from baseline with equal or fewer medications than preoperatively.
Failure was defined as reoperation for IOP control, complications and loss of light perception vision.
Postoperative outcomes
Mean IOP decreased 43%, from about 26 mm Hg before second tube shunt insertion to 15 mm Hg at 1 year.
“This carried on to about 3 years,” Hu said.
Average medication use decreased significantly, from 3.59 preoperatively to 1.71 at 12 months.
“But [there was] a general trend to an increase in glaucoma medications over time after the second tube shunt,” Hu said.
The failure rate was 55.4% at a median interval of 2 years.
“Compared to some of the prior similar studies, the criteria for success was slightly more stringent in our study,” Hu said.
Of 26 failures attributed to poor IOP control, four required a third tube shunt and one required laser cyclophotocoagulation.
“Therefore, five out of 26 required further surgical intervention for IOP control,” she said. “The rest were maintained on the medications.”
Three cases of tube exposure and one case of plate exposure required revision surgery. Tube malposition, plate migration and prolonged hypotony were also reported.
The most common complications were serous choroidal detachment, worsening corneal edema and diplopia, Hu said. – by Matt Hasson