Because the conjunctiva is soft and elastic, however, it offers little resistance to the aqueous that flows out of the device during the early postoperative period. As a result, overfiltration is possible in the short term. The implant can erode through the conjunctiva over the long term and lead to extrusion of the device. For these reasons, we prefer implanting the Ex-PRESS mini glaucoma shunt under a scleral flap, which offers more resistance to aqueous outflow and reduces the risk of device extrusion, although this technique does prolong the operating time as compared with the conjunctival technique.
With the authorization of the Ethics Committee of the University of the Witwatersrand in Johannesburg, South Africa, and of Optonol Ltd., we conducted a pilot study to evaluate the benefits of implanting the Ex-PRESS mini glaucoma shunt under a scleral flap. All subjects signed an informed consent prior to undergoing surgery. This article details our surgical technique and shares our results after 2 years of follow-up.
SURGICAL TECHNIQUE
First, we create a fornix-based conjunctival flap with a single, radial, relaxing incision in an upper quadrant. Next, we lift a 5 X 5-mm, limbal-based scleral flap of approximately 50% depth while taking care that the dissection passes the vascular arcade and reaches clear cornea (Figure 1). We apply mitomycin C (MMC) 0.02% under the scleral flap in high-risk cases but limit the MMC exposure to the scleral bed in order to preserve a healthy conjunctiva. Using a 25-gauge needle, we perforate the anterior chamber under the scleral flap, in the center of the blue-grey transitional zone between the white sclera and clear cornea (Figure 2). We are careful to hold the needle parallel to the iris plane while making this pre-perforation in order to ensure proper positioning of the shunt.
Figure 1. At 50% depth, the 5 X 5-mm trapezoidal scleral flap extends into clear cornea.
Figure 2. The authors use a 25-gauge needle to make a pre-perforation at the center of the transitional area between white sclera and clear cornea.
After filling the anterior chamber with a high-viscosity viscoelastic material through either the pre-perforation or a separate paracentesis, we insert the Ex-PRESS mini glaucoma shunt through the pre-perforation and into the anterior chamber (Figure 3). Next, we securely suture the scleral flap over the implant at its distal corners and at one distance between the limbus and the end of the scleral flap (Figure 4). We suture the conjunctiva back into place with one or two buried sutures. We use either 10–0 or 9–0 nylon for all sutures.
Figure 3. Under direct visualization, the authors insert the Ex-PRESS mini glaucoma shunt through the pre-perforation.
Figure 4. The authors secure the scleral flap with a single suture at the apex and two sutures at one distance from the limbus.
Postoperative care includes instilling steroid-antibiotic combination drops q.i.d. until the patient's IOP reaches 12 mm Hg. Thereafter, the patient uses nonsteroidal anti-inflammatory drops t.i.d. for 6 weeks.
SUBJECTS
Using the scleral-flap technique, we implanted the Ex-PRESS mini glaucoma shunt in 24 eyes of 23 patients between August 2001 and March 2003. Twenty-one of the patients suffered from primary open-angle glaucoma, and two had pseudoexfoliation glaucoma. All the patients were at high risk for glaucoma surgery failure. Of the nine white patients, all but one had a history of at least one previous failed filtration surgery. The remaining 14 subjects were of races with a known risk for filtration surgery failure (eight black, four Indian, one Asian, and one of mixed white and black race). The subjects' mean age was 60.7 years ±14.9 SD, with a range of 30 to 78 years.
RESULTS
We used MMC 0.02% under the scleral flap of all the patients. IOP decreased from a mean preoperative level of 27.2 ±6.9 mm Hg to 13.7 ±2.9 mm Hg at 12 months. The average IOP was 16.6 ±3.2 mm Hg at 18 months. These changes in IOP occurred without additional medical therapy, except in the case of a single patient who needed betaxolol. The majority of the patients (70%) did not show large filtering blebs, but the rest had mildly elevated, healthy, diffuse blebs.
Complications occurred in six patients. The shunt touched the iris in the eyes of two patients, and one patient developed a postoperative hyphema that required an anterior chamber washout 4 days postoperatively. Three patients experienced postoperative hypotony with shallow anterior chambers, and two of them developed choroidal effusions. In all three patients, these complications resolved spontaneously, and further surgery was not required. All complications occurred in the early stages of the study when the scleral flap was not sutured as securely as it was later in the trial.
CONCLUSIONS
Our pilot study demonstrates that the scleral implantation technique described herein can minimize the potential short-term and long-term complications associated with implantation of the Ex-PRESS mini glaucoma shunt under a limbal-based conjunctival flap while still providing optimal IOP control. Although it prolongs operative times, implanting the device under a scleral flap is still simpler and safer than performing a trabeculectomy. The latter procedure requires the surgeon to punch a hole in the limbal area under the scleral flap and perform a peripheral iridectomy, and trabeculectomies can result in vitreous exposure when the hole is placed too posteriorly. Implanting the Ex-PRESS mini glaucoma shunt through a small pre-perforation avoids this complication.
We found that aqueous was shunted from the anterior chamber into the subscleral space in a controlled manner through the 50-µm lumen of the Ex-PRESS mini glaucoma shunt. Most of the aqueous is probably reabsorbed intrasclerally via aqueous veins under the scleral flap and in the MMC-treated scleral bed. We find that implanting the Ex-PRESS mini glaucoma shunt under a scleral flap combines the advantages of penetrating and nonpenetrating glaucoma surgery.
Elie Dahan, MD, is the former Head of the St. John Eye Hospital in Johannesburg, South Africa. Dr. Dahan is Senior Lecturer and Honorary Senior Consultant (Glaucoma and Pediatric Ophthalmology) for the Department of Ophthalmology at the University of the Witwatersrand in Johannesburg, South Africa. He does not hold a financial interest in the product or companies mentioned herein. Dr. Dahan may be reached at +27 11 880 4200; dahaneli@cis.co.za.
Trevor Carmichael, MD, PhD, is Professor of Ophthalmology and Chairman of the Department of Ophthalmology at the University of the Witwatersrand in Johannesburg, South Africa. He does not hold a financial interest in the product or companies mentioned herein. Dr. Carmichael may be reached at carmichaeltr@medicine.wits.ac.za.
