How Well Do Glaucoma Drainage Devices Work?
Short answer: it depends upon the reason an aqueous shunt was chosen.
Battling an Old Foe
Although glaucoma drainage devices have been around for almost as long as trabeculectomy, they have not gained as wide an acceptance among eye surgeons. For almost forty years glaucoma drainage devices were viewed as the “salvage” option to be used when everything else had failed or could be expected to fail. It should be no surprise, then, that the published success rates were dismal. Still, compared to the alternatives it at least had a chance of success (however limited). This all changed at the turn of the millennium.
In the first decade of the 21st century a landmark study was published which changed the way many glaucoma surgeons viewed glaucoma drainage devices. Called the Tube Versus Trabeculectomy (TVT) study, it compared the results of surgery performed on the eyes of patients who had already had eye surgery. The “tube” used in this study was the 350mm2 Baerveldt®. What did the study show? Something so unexpected that many glaucoma surgeons were shocked into disbelief: that aqueous shunts could be just as effective as trabeculectomy with Mitomycin-C (MMC).
Like most glaucoma treatment studies, the TVT defined success based on final intraocular pressure (IOP). Average IOP one year out from surgery was near identical between those who had the Baerveldt® shunt (12.4mmHg) and those who had trabeculectomy with MMC (12.7mmHg). This similarity was maintained for five years as the average IOP and number of medications required for IOP control was still similar between tubes and trabs. However, some important differences were noted. Just over 50% of the trabeculectomies were still controlling the IOP whereas 70% of the tubes were still successful. Additionally, three times as many trabeculectomies required re-operation as tubes.
So it appears that at least in eyes that have had prior surgery the hard working underdog of glaucoma surgery (tube) has won a round against the previously undisputed champion of glaucoma surgeries (trab).
How Long Does the Effect Last?
Evidence suggests that glaucoma drainage devices fail at a rate of approximately 10% per year. This is similar to the rate of failure for trabeculectomy. By five years after surgery it can be expected that approximately 30-50% of glaucoma drainage devices will have “failed”. Nevertheless, aqueous shunts have been documented to last for more than twenty years.
1) Gedde SJ, Schiffman JC, Feuer WF, et al. Tube Versus Trabeculectomy Study Group. Treatement outcomes in the tube versus trabeculectomy study after one year of follow-up. Am J Ophthalmol. 2007;143:9-22.
2) Gedde SJ, Schiffman JC, Feuer WJ. Treatment Outcomes in the Tube Versus Trabeculectomy (TVT) Study After Five Years of Follow-up. 2012 [Article in Press].
3) Minckler DS, Francis BA, Hodapp EA, et al. Aqueous Shunts in Glaucoma. Ophthalmol. 2008;115(6):1089-1098.
4) Mills RP, Reynolds A, Emond MJ, et al. Long-term survival of Molteno glaucoma drainage devices. Ophthalmol. 1996;103:299-305.
Gedde SJ, Schiffman JC, Feuer WJ, et al. Treatment Outcomes in the Tube Versus Trabeculectomy (TVT) Study After Five Years of Follow-up. Am J Ophthalmol. 2012 [Article in Press].
5) Ah-Chan JJ, Molteno AC, Bevin TH, Herbison P. Otago Glaucoma Surgery Outcome Study: follow-up of young patients who underwent Molteno implant surgery. Ophthalmol. 2005;112:2137-