By Commentary by Adam C. Reynolds, MD
The last 10 years have seen a significant increase in the use of classic aqueous shunt surgery as an alternative to trabeculectomy. With the type of shunts available more varied and techniques to prevent complications more refined, tube shunt surgery has become a reasonable and sometimes better alternative to trabeculectomy for some refractory cases of glaucoma.
The authors of this Academy-produced Ophthalmic Technology Assessment have provided an evidence-based summary of specific questions and answers regarding tube shunt surgery by using Cochrane meta-analytical criteria and analyzing published literature. Their analysis, which is based on level I evidence, concludes that aqueous shunts are a viable alternative to trabeculectomy or cyclodestructive procedures for many cases of refractory glaucoma.
Seventeen studies published from 1992 through 2007 were included in the study. There was level I evidence, the rating assigned to well-designed and well-conducted randomized clinical trials, of little obvious difference when comparing IOP control and duration of benefits of aqueous shunts and trabeculectomy. Failure rates for treatments averaged about 10 percent per year in this analysis.
There was little consensus regarding appropriate indications for aqueous shunt surgery, as indications have broadened recently. However, shunt surgery has been recommended for failed primary trabeculectomy and as primary surgery in certain conditions, such as trauma, chemical burns, and pemphigoid, a finding with level III evidence, the rating for case series, case reports and poor-quality case control and cohort studies. There is sufficient level I evidence that using intraoperative antifibrotic agents or systemic corticosteroids as adjuncts to tube shunt procedures does not improve long-term function or decrease complications.
There are too few direct comparisons of sufficient quality to assess relative differences in efficacy or complication rates for various types and brands of shunts. Research has suggested that implants with larger surface areas provide better IOP control. There is insufficient published data to assess whether there is a decreased risk of hypotony with valved tube shunts versus nonvalved shunts.
The major long-term complications of anterior chamber tube shunts are endothelial failure and erosion of the shunt through the conjunctiva usually close to the corneal limbal junction. Other less common complications include short-term hypotony, excessive capsule fibrosis and failure, plate erosion and strabismus. Infections associated with tube shunt surgery were found to be rare, particularly when compared to rates of infections associated with trabeculectomy with antifibrotic agents.
The authors of this review acknowledge that direct comparisons of different tube shunts in high-quality multicenter studies may be useful to assess the best design parameters for increasing performance and decreasing complications. Further work to improve tube shunt function over time should also focus on improving material biocompatibility and alternative postoperative management techniques.
Discuss this article
Tell us your thoughts on this article, and see your ideas posted online in our new ONE Opinion feature. Don't forget to include the article title in the subject line.
Financial Disclosures
Dr. Reynolds has received consulting fees from Allergan, Inc., iScience Interventional, Optonol Ltd., and Transcend Ltd. He has received lecture fees from Alcon Laboratories, Inc., Allergan, iScience Interventional, Optonol, and Pfizer Ophthalmics.