Aqueous shunt use increasing as indications appear to broaden

"As experience with shunts has increased, glaucoma specialists have gained a greater appreciation for their advantages while at the same time becoming more aware of the disadvantages of filtering procedures," explained Dr. Gedde, associate professor of ophthalmology, Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami. "Now aqueous shunts are being used commonly as a primary surgical procedure in high-risk glaucomas. One can even argue a reasonable case for considering aqueous shunts as a primary surgical treatment for low-risk eyes."

However, for eyes with prior trabeculectomy, extracapsular or intracapsular cataract extraction, penetrating keratoplasty, scleral buckle procedure, or pars plana vitrectomy, and for those with uveitic or neovascular glaucoma, the proportions of surgeons who would choose to implant a glaucoma shunt increased by 9% to 16%. For all clinical settings combined, the average number of surgeons who would choose to implant a glaucoma shunt nearly doubled over 6 years from 17% to 29%.

Medicare utilization data provided by University of Oklahoma glaucoma specialist Gregory L. Skuta, MD, also show more and more aqueous shunts are being implanted. Tracing the numbers of glaucoma surgeries performed between 1994 and 2003, the annual number of trabeculectomies declined from more than 60,000 to about 37,000. Data on annual aqueous shunt procedures showed there was a steady, gradual rise from about 2,300 to nearly 8,000.

"The decrease in filtering surgery is largely attributable to advances in medical therapy over that 10-year period," Dr. Gedde said. "Trabec-ulectomy is still performed much more often than implantation of an aqueous shunt. However, it is still interesting to see that during a period when the number of trabeculectomies performed fell dramatically, the number of shunt procedures continued to increase."

Disadvantages of trabeculectomy and advantages of shunt procedures may help to explain the trends in practice patterns. Trabeculectomy requires the presence of an unscarred conjunctiva, mandates intensive postoperative care, and as glaucoma surgeons are becoming increasingly aware, is associated with serious late complications of bleb infections and bleb leaks as well as loss of efficacy over time.

"Aqueous shunts are not without their problems, but they do not require virgin conjunctiva and certainly require less intensive postoperative care," Dr. Gedde said. "Shunts are also associated with a lower risk of late infections, and many glaucoma surgeons have the impression that they have a more durable effect that is more likely to persist if the patient undergoes subsequent ocular surgery."