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Miniature glaucoma implant compares favorably with trabeculectomy
The shunt showed a lower rate of early postop hypotony than trabeculectomy when implanted under a partial-thickness scleral flap.
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A miniature glaucoma device implanted under a partial-thickness scleral flap lowers IOP as effectively as standard trabeculectomy, with lower rates of early postoperative hypotony and choroidal effusions, according to a study.
Investigators at the University of Tennessee Health Science Center compared the techniques in a single-center, retrospective comparative series to evaluate how the Ex-PRESS mini glaucoma shunt (Optonol) performs when compared with standard methods.
During early clinical trials, the device was implanted near the limbus and under the conjunctiva to drain aqueous from the anterior chamber into the subconjunctival space, according to the authors. However, that approach caused adverse events, including hypotony and erosion of the conjunctiva over the device.
In this study, the researchers chose to use the under scleral flap (USF) technique for implantation of the Ex-PRESS mini glaucoma shunt. Using this technique, a partial-thickness scleral flap was performed to determine whether the outcomes would improve.
“The scleral flap may provide resistance to aqueous outflow and may minimize the risk of conjunctival erosion,” Peter J.G. Maris Jr., MD, and colleagues stated in the study published in the Journal of Glaucoma.
The study included 50 eyes of 49 patients consecutively implanted over an 11-month period with the Ex-PRESS device and 50 matched control eyes of 47 patients treated with trabeculectomy during an overlapping 2-year period. In cases with visually significant cataract, trabeculectomy was combined with a cataract procedure.
Patients included in the study were 18 years and older with uncontrolled IOP on maximally tolerated medical therapy.
The researchers collected postop data for IOP, medications, visual acuity and complications at day 1, days 3 to 5, weeks 1 and 2 and months 1, 2, 3, 6, 12 and 15. Average follow-up was 11 months for both groups, with a minimum of 3 months, according to the study.
They defined surgical success as an IOP of 5 mm Hg or more and 21 mm Hg or less with or without glaucoma medications and without further surgery.
Similar IOP reduction
Mean preoperative IOP was 26 mm Hg in both groups, according to the results. At 3 to 5 days, 1 and 2 weeks and 1 and 3 months postoperatively, the mean IOPs were statistically significantly lower in the trabeculectomy group than in the Ex-PRESS group.
The mean IOPs did not differ significantly between both groups at the other time points, the authors said. After 3 months, the percentage decrease in IOP ranged from 40% to 47% in the Ex-PRESS group and 29% to 45% in the trabeculectomy group.
At final follow-up, the success rate was 90% in the Ex-PRESS group and 92% in the trabeculectomy group.
“Although it is possible that we did not detect differences in efficacy between these techniques due to study design, our findings indicate that similar success can be achieved with both Ex-PRESS implantation under a scleral flap and trabeculectomy,” the authors wrote.
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Images: Optonol |
Less hypotony, fewer effusions
Although trabeculectomy provided lower initial IOPs than the Ex-PRESS implant, there was a significantly higher rate of early postop hypotony in the trabeculectomy group compared with the Ex-PRESS group, according to the authors.
The results showed there were two cases of early postop hypotony in the Ex-PRESS group compared with 16 cases in the control group, demonstrating the advantages of placing the device under a scleral flap rather than directly under the conjunctiva, the authors said.
They also reported four choroidal effusions in the Ex-PRESS compared with 19 in the trabeculectomy group. One eye in the Ex-PRESS group and five eyes in the trabeculectomy group required surgical drainage of the effusions.
According to the authors, the scleral flap provided resistance to aqueous flow in both groups, but the 50 µm lumen in the Ex-PRESS device may have provided the additional resistance that lead to slower initial decrease of the IOP in conjunction with the low rates of early postop hypotony and choroidal effusions.
Suture tension or tighter scleral flap seal may have also played a role in the study outcomes, the authors said.
“Although both groups were observed to have little or no flow of aqueous around the flap at the end of surgery, alternative explanations for these findings include less suture tension on the flap in the trabeculectomy group, or a tighter seal of the flap against the Ex-PRESS implant,” they said.
Surgical technique
The surgical procedure included preparation in all eyes of a triangular scleral flap at 50% depth measuring 3 mm at the limbus, according to the study. Mitomycin C 0.4 mg/mL was then applied under the scleral flap for 1 to 2 minutes.
The trabeculectomy procedure diverges from the Ex-PRESS implantation when a sclerostomy is created under the scleral flap with two to three punches with a Kelly Descemet’s punch followed by surgical peripheral iridectomy, according to the authors.
This step is skipped during implantation of the Ex-PRESS device. Instead, the surgeon inserts the implant through a 27-gauge needle tract at the limbus without the injection of viscoelastic into the anterior chamber at the end of the procedure.
“This may reduce the intraoperative time and minimize variability of results in different patients for implantation of the Ex-PRESS device compared with trabeculectomy,” the authors said.
The scleral flap is then closed in both groups with three interrupted 10-0 nylon sutures with similar tension followed by closure of the conjunctiva with a running 9-0 polyglactin suture on a tapered needle.
For more information:
- Peter A. Netland, MD, PhD, the corresponding author of this study, can be reached at Hamilton Eye Institute, University of Tennessee Health Science Center, 930 Madison Ave., Suite 100, Memphis, TN 38163 U.S.A.; +1-901-448-7885; fax: +1-901-448-9350. The authors have no proprietary interest in the Ex-PRESS implant.
- Optonol Ltd., maker of the Ex-PRESS mini glaucoma shunt, can be reached at Communication Center, Neve Ilan 90850, Israel; +972-2-534-9666; fax: +972-2-534-9660; e-mail: support@optonol.com; Web site: www.optonol.com.
Reference:
- Maris PJG Jr, Ishida K, Netland PA. Comparison of trabeculectomy with Ex-PRESS miniature glaucoma device implanted under scleral flap. J Glaucoma. 2006;16:14-19.
- Jared Schultz is an OSN Staff Writer who covers all aspects of ophthalmology. He focuses geographically on Europe and the Asia-Pacific region.