POAG study finds more complications with drainage devices than with trabeculectomy

September 1, 2008

In a retrospective, longitudinal cohort analysis of 14,491 Medicare beneficiaries who underwent one of the three incisional glaucoma surgeries between 1994 and 2003, those who underwent glaucoma drainage implant surgery were more likely to have severe complications, low vision, and progression to blindness than those who had a trabeculectomy. The results run counter to an ongoing randomized controlled trial of the procedures.

Key Points

Dr. Stein and colleagues conducted a retrospective, longitudinal cohort analysis of the records of more than 14,000 Medicare beneficiaries between 1994 and 2005. All of the subjects had a diagnosis of glaucoma. The researchers examined the rates of complications of the three major incisional glaucoma surgeries: trabeculectomy, trabeculectomy with prior scarring, and implantation of a glaucoma drainage device.

"We compared rates of severe and less-severe complications, need for additional surgery, and blindness," Dr. Stein said. "Our main finding was that patients in the glaucoma drainage device group were more likely to experience severe and less-severe complications compared with the two trabeculectomy groups."

Dr. Stein said he suspects that the differences identified by the researchers may be related to case-mix variables that they couldn't capture in the administrative claims database.

"Our study kind of complements the Tube vs. Trabeculectomy study, which is an ongoing randomized, controlled trial comparing trabeculectomy and tube shunt surgery," he said. "That study is showing a similar reduction in IOP between trabs and tubes, but fewer complications in the tube group, whereas we've found an increased rate of complications in the tube group.

"So now we're trying to understand what's responsible for the difference. Is it case mix variables, or are there really patients receiving tubes who really are at increased risk of experiencing complications compared with patients who undergo trabeculectomy?"

Dr. Stein and colleagues examined the records of 14,491 Medicare beneficiaries, aged 68 to 96 years, who underwent one of the three incisional (non-laser) glaucoma surgeries between 1994 and 2003, with follow-up through 2005. They examined the rates of serious adverse outcomes such as endophthalmitis, suprachoroidal hemorrhage, and retinal detachment; less-serious adverse outcomes such as hypotony, corneal edema, and choroidal detachment; and the need for additional glaucoma surgeries.

Among their findings:

The full results are reported in Ophthalmology (2008;115:1109-1116).

'Sicker eyes'

Why the drainage devices group would not have fared as well as the other two groups is a question that he and his fellow researchers have struggled with, Dr. Stein told Ophthalmology Times.

"Based on the initial results of the Tube vs. Trabeculectomy study and our own clinical experience, we would have hypothesized that the trabeculectomy group would have had the highest rate of complications, yet our results showed otherwise," he said. "I think our main explanation is that patients-at least in this series, which was looking primarily at patients in the 1990s and early 2000s-had a primary trabeculectomy and then had a trabeculectomy with scarring before they underwent glaucoma drainage device surgery. So the eyes that eventually required tubes were sicker eyes that had already undergone a number of surgeries."

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