Approved by the FDA, the Ex-Press Mini Glaucoma Shunt (Optonol Ltd., Neve Ilan, Israel) is a small device without a valve that lowers the IOP by shunting aqueous from the anterior chamber into the subconjunctival space. In experimental studies, the device showed good biocompatibility.1
During initial clinical trials, the device was placed near the limbus without a scleral flap, which was associated with erosion through the conjunctiva, hypotony, and other adverse effects.2-6 These problems have been minimized by placing the device under a partial-thickness scleral flap,7,8 which provides resistance to aqueous outflow and reduces the risk of conjunctival erosion. Unlike during trabeculectomy, the surgeon performs no iridectomy and no sclerectomy when implanting the Ex-Press device under a partial-thickness scleral flap. Despite similarities between the procedures, the implantation of the Ex-Press does not involve the excising of trabecular tissue.
This article focuses on the device's implantation and its results in studies and the clinic.
TECHNIQUES
After preparing a fornix- or limbus-based conjunctival flap, surgeons create a partial-thickness scleral flap, similar to that used for trabeculectomy,8 and then apply mitomycin C to the area according to their preference. The Ex-Press is placed at the limbus, under the flap, through a 25-gauge needle tract.
Most commonly used is the P model (Figure 1). The R model, which has a longer stem, can be placed through a 27-gauge needle tract (Figure 2). Most surgeons use the device with a 50-µm internal diameter, although a version with a 200-µm internal diameter is available. The Ex-Press now comes preloaded on an inserter, which helps to guide the device into the needle tract and releases the device when it is in the proper position.
After the Ex-Press' insertion, the surgeon should confirm that the tube's tip is properly positioned in the anterior chamber. If the tip is in the corneal stroma, the device must be removed and repositioned. The surgeon closes the flap with interrupted 10–0 nylon sutures (if laser suture lysis is planned) or with releasable sutures. The conjunctival flap is closed in the same manner as for trabeculectomy. In most instances, a viscoelastic is not needed during the procedure.
RESEARCH RESULTS
Maris et al compared the results of trabeculectomy in 50 eyes with the results of the Ex-Press' implantation under a partial-thickness scleral flap in 50 eyes.8 In this study, the mean IOP in the immediate postoperative period was lower after trabeculectomy than after the device's implantation, although the long-term IOP control and surgical success rates were similar. Early postoperative hypotony and its sequelae were less common in the eyes that received the Ex-Press than in those that underwent a trabeculectomy.
In a series of 345 eyes, investigators compared the results obtained with the Ex-Press under a scleral flap (241 eyes) versus its implantation in combination with cataract surgery (114 eyes).9 IOP control was similar in both groups, although a few individual time points had a significantly lower mean IOP after the Ex-Press' implantation alone versus in combination with cataract surgery. In this study, the device was effective alone or as a combined procedure with cataract surgery. The most common device-related complication in this series was a blocked tube, which occurred in six eyes (1.7%). Treatment with an Nd:YAG laser effectively removed the obstructing material in all cases. The obstruction was not visible in most of these eyes, although Nd:YAG laser treatment (1 to 2 mJ) of the tube's tip resulted in a dispersion of whitish particles near the tube's tip, an elevation of the bleb, and a reduction in the IOP.
LONG-TERM COMPLICATIONS
Placing the Ex-Press under the conjunctiva can be associated with conjunctival erosion over the implant such that exposure and even extrusion of the device occurs.10,11 Placing the device under a partial-thickness scleral flap minimizes but does not completely eliminate the possibility of its exposure.12 Conjunctival erosion and the implant's exposure are treated with the removal of the device. The Ex-Press can also dislocate into the anterior chamber,9,13,14 usually necessitating the device's removal. Long-term corneal problems are possible but have not been common in the studies reported to date. Long-term bleb-related problems are probably similar to those observed after trabeculectomy.
The Ex-Press is not ferromagnetic. In vitro testing has shown no movement of the device in an MRI field. Thus, patients with the device may have an MRI scan.
CLINICAL EXPERIENCE
When implanted under a scleral flap, the Ex-Press has certain advantages compared with trabeculectomy. The former causes less trauma to ocular tissue and less inflammation, because its implantation involves no sclerectomy or peripheral iridectomy. Because the internal diameter of the device is the same from procedure to procedure (unlike the preparation of a sclerostomy in trabeculectomy), the Ex-Press' placement has predictable results. Perhaps due to the device's resistance to aqueous flow, there are fewer complications, especially hypotony in the early postoperative period and its sequelae. Because the procedure is simpler and has fewer steps compared with trabeculectomy, the device's implantation requires less intraoperative time.
The disadvantages of the Ex-Press include its cost and the potential for device-related complications. The results obtained by the author and his colleagues suggest that device-related complications are uncommon when the Ex-Press is implanted under a partial-thickness scleral flap.
The Ex-Press may be used for primary glaucoma surgery and, less commonly, for secondary surgery. Relative contraindications include young age (because of the lack of long-term biocompatibility studies) and chronic inflammation (because of the potential for the tube's/device's blockage).
CONCLUSION
When implanted under a scleral flap, the Ex-Press is effective by itself or in combination with cataract surgery. The device is as effective for long-term IOP control as trabeculectomy, and it minimizes early postoperative hypotony and its sequelae. Device-related complications are uncommon when the device is implanted under a partial-thickness scleral flap.
Peter A. Netland, MD, PhD, is the Siegel professor and the director of the Glaucoma Service at the Hamilton Eye Institute of the University of Tennessee Health Science Center in Memphis. He acknowledged no financial interest in the products or company mentioned herein. Dr. Netland may be reached at (901) 448-5492; pnetland@gmail.com.
