Mini glaucoma shunt viable surgical alternative

October 15, 2008

Surgical outcomes were compared in a retrospective study of 76 eyes with a miniature glaucoma shunt (Ex-PRESS, Optonol) implanted and 77 eyes that underwent standard trabeculectomy. The two procedures were associated with similar IOP-lowering efficacy, but the shunt procedure had a benefit for reducing the risk of hypotony.

Key Points

Dr. Herndon compared the outcomes of the two glaucoma procedures performed in his own hands in a retrospective chart review. His study included 76 consecutive shunt procedures in 69 patients performed between June 2006 and July 2007 and 77 consecutive standard trabeculectomy surgeries performed in 65 patients between June 2005 and May 2006.

"This study has the inherent weaknesses of its retrospective design, and another limitation is that different shunt models and different conjunctival closure techniques were used," said Dr. Herndon. "However, its results are consistent with a published retrospective, comparative study by Peter Netland, MD, and colleagues who also reported similar IOP-lowering efficacy for the two procedures, but with a higher rate of hypotony in eyes undergoing standard trabeculectomy. These findings suggest the [miniature] device is a viable alternative to conventional trabeculectomy."

The two surgical groups in Dr. Herndon's study were similar with respect to baseline demographic and clinical features. Just over half of the eyes in the shunt group (53%) had previous incisional surgery, predominantly prior trabeculectomy or cataract surgery, and that history was present in a slightly higher proportion of patients undergoing standard trabeculectomy (61%), although the difference between groups was not statistically significant.

Outcomes data were extracted from visits at 1 day, 1 week, 1 month, and most recent visit. IOP analyses showed that beyond the first day after surgery, no significant differences were found comparing mean IOP in the two groups. At the most recent visit, mean IOP was 11.3 mm Hg in the shunt group and 10.8 mm Hg in the standard trabeculectomy group.

Failure, defined as IOP of 5 mm Hg or less, IOP exceeding 21 mm Hg, or a need for further surgery, was more common in the eyes that had standard surgery compared with the shunt group, 32% versus 22%, respectively, although the difference in rates did not achieve statistical significance. Considering eyes that had failure because of hypotony (IOP < 5 mm Hg), however, a significant difference existed between groups, with a fourfold higher rate in the standard trabeculectomy group compared with the eyes that received the miniature shunt, 16% versus 4%, respectively. No between-group differences were found in the rates for the other failure criteria.

More bleb leaks

Regarding other complications, the shunt surgery was associated with more bleb leaks than standard trabeculectomy.

"I believe this difference is due to a change in technique I made recently from a limbal-based to a fornix-based procedure in the shunt group. There are very few eyes in the standard trabeculectomy group that had fornix-based surgery," Dr. Herndon said.

He also analyzed outcomes separately for the subgroup of eyes that underwent combination glaucoma-cataract surgery. Phacoemulsification was performed at the time of the glaucoma procedure in 19 eyes that had the shunt implanted and 20 eyes that underwent standard trabeculectomy. Throughout follow-up, mean IOP was significantly lower in eyes that underwent phacoemulsification combined with shunt placement than in eyes that had cataract surgery combined with standard trabeculectomy. At the most recent visit, no significant IOP difference existed between these groups, however.

Another subgroup analysis considered differences in IOP control between patients who received one model of the shunt (X-200) versus another model (X-50), which has a more narrow lumen.

"Interestingly, during the early follow-up, IOP was significantly lower in eyes with the [model with the more narrow lumen]. However, at the most recent visit, there was no significant difference between groups. More study is needed to determine the ideal model selection for the target level of IOP control," Dr. Herndon said.

The miniature shunt initially was designed to be placed under the conjunctiva, but the technique has evolved to the use of a subscleral flap placement to reduce the risk of erosion. It has been available in three models (R, T, and X). Earlier this year, the manufacturer introduced a new model (P) that features a slit in the plate to facilitate posterior filtration. Previously, a new delivery system was developed that makes release of the shunt from the introducer easier.

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