TREATING GLAUCOMA

Applying a New Technique to a Tried-and-true Procedure

Trabeculectomy with the Ex-PRESS mini glaucoma shunt lowers IOP and reduces the risk of complications.

By Michael C. Herceg, D.O.

► Ophthalmologists have considered trabeculectomy the gold standard for surgically lowering IOP since J.E. Cairns, M.D.,¹ introduced the procedure in 1968. Since then, several advances and changes in technique have been introduced to improve the success rate of the procedure, including intraoperative use of antimetabolites in the late 1980s and early 1990s.^2-4

More recently, a new procedure in trabeculectomy surgery has come to the fore — the Ex-PRESS mini glaucoma shunt (Optonol Ltd., Neve Ilan, Israel) implanted under a scleral flap. This shunt, used in place of standard trabeculectomy, has been associated with decreased risk of early postoperative complications, such as hypotony and choroidal effusion.⁵

To date, Robert J. Noecker, M.D., and I have implanted about 30 Ex-PRESS shunts in patients at the University of Pittsburgh Medical Center's Eye and Ear Institute. We've been using this technique in patients whom we've considered candidates for traditional trabeculectomy surgery, and in a few cases, we've combined it with phacoemulsification and intraocular lens implantation.

In this article, I'll discuss the efficacy and safety of the Ex-PRESS mini glaucoma shunt, describe the technique for implanting the device and review surgical considerations when performing this procedure.

Device History

Originally developed in 1998, the Ex-PRESS mini shunt is a non-valved device that's about 3 mm in length and made of medical grade stainless steel. The earliest devices were inserted by placing them in the anterior chamber, directly under the conjunctiva near the limbus. These surgeries, however, were associated with high rates of hypotony and conjunctival erosion over the shunt, among other problems.

In 2005, Dahan and Carmichael⁶ introduced the technique of placing the Ex-PRESS shunt under a scleral flap. Since then, the device has gained popularity, as physicians have continued to learn more about the procedure's safety and efficacy.

Efficacy and Safety

We know from prior studies that an Ex-PRESS shunt placed under a scleral flap can lower IOP significantly.

In a study⁵ of 100 patients, the average post-op IOP in the Ex-PRESS shunt group (13.7 mm Hg +/- 6.4 mm Hg from an average of 26.2 mm Hg +/- 10.5 mm Hg pre-op) was similar to the trabeculectomy arm (12.9 mm Hg +/- 8.5 mm Hg post-op from an average of 25.5 mm Hg +/- 9.9 mm Hg pre-op).

In addition, the success rates at 15 months were similar for both groups (90% Ex-PRESS group vs. 92% trabeculectomy), as were the number of postoperative glaucoma medications needed. However, the rate of early post-op hypotony and choroidal effusion was significantly higher in the trabeculectomy group compared with the Ex-PRESS shunt implant arm.

Fewer Complications

The Ex-PRESS shunt has been associated with fewer early post-op complications, such as hypotony, hypotony maculopathy and choroidal effusions or hemorrhage (potentially requiring surgical drainage). One possible explanation for the lower complication rate is the size of the Ex-PRESS mini shunt. It has a fixed, internal lumen diameter of 50 microns, which is smaller than the size of a typical sclerostomy (opening into the anterior chamber) for a trabeculectomy. This smaller diameter is believed to provide increased resistance to aqueous outflow in the immediate post-op period, reducing the risk of hypotony.

There's also the possibility that the scleral flap makes a tighter seal with the Ex-PRESS shunt plate, which allows for a more watertight suture closure of the scleral flap early on. Of course, this tighter seal may require laser suture lysis (LSL) in order to achieve an adequate IOP-lowering effect. However, the advantage is that the LSL could be performed under more controlled conditions — once the eye has had a chance to stabilize after surgery.

As has been the case in published reports, we've seen less of the extremely low (0-3 mm Hg) early IOPs, although in some patients, IOPs have been as low as 5 mm Hg to 9 mm Hg, with large, elevated posterior diffuse blebs on post-op day 1.

Additionally, the eyes of patients with the Ex-PRESS shunt have had less anterior chamber inflammatory reaction and/or hyphema early on. We attribute this to the fact that the iris isn't cut for an iridotomy, and no scleral tissue is removed. Insertion of the Ex-PRESS shunt seems to be less traumatic to the eye, and can be done more precisely and quickly than the creation of a sclerostomy and iridectomy as in standard trabeculectomy surgery.

As mentioned previously, in cases where the post-op IOP is higher than ideal, you can perform laser suture lysis and bleb needle revisions using the same method and technique that's used for traditional trabeculectomy.

Implantation Technique

The initial steps for implanting the Ex-PRESS mini shunt under a scleral flap are very similar to a standard trabeculectomy. Typically, we place a superior clear corneal bridle suture first to rotate the eye downward for maximum exposure of the superior conjunctiva. We use a fornix-based conjunctival peritomy (approximately 60° arc) to create a 3-mm trapezoid-shaped scleral flap (Figure 1). The flap is continued anteriorly at 50% to 75% scleral depth, up to the blue-zone of clear cornea. Next, we apply topical mitomycin (0.2 mg/mL) for 2 minutes, and copiously irrigate the eye with two bottles of Balanced Salt Solution.

Figure 1: A fornix-based conjunctival peritomy and trapezoidal scleral flap are created in the same manner as for trabeculectomy. The flap is carried anteriorly to the blue zone of the clear cornea. Sponges soaked in Mitomycin C are placed subcon-junctivally as posteriorly as possible.

Up to this point, our surgical procedure is exactly the same as the procedure used in a classic trabeculectomy. Here, however, rather than entering the anterior chamber through the blue zone with a paracentesis blade for the scleral punch, we instead insert a 27-gauge needle. The target location for entry is the posterior border of the blue zone, and the approach pathway is roughly along the iris plane (Figure 2). This needle track serves as a pilot hole for inserting the Ex-PRESS shunt.

Figure 2: After creation of a pilot hole with a 27-gauge needle, the device is inserted with its prepackaged inserter. The placement position is the posterior edge of the blue-zone, roughly in the plane of the iris. The device is inserted up to its plate (past its barb), and once it's in good position, the release button on the injector is pressed, which disengages the device.

The device comes with an injector — somewhat similar to a punctal plug inserter. You simply push the device into the eye with the inserter, going up to the hub, and past its barb, which locks it into place. Then, press the release button on the inserter to disengage the shunt from the injector.

To facilitate the insertion of the device, you can use viscoelastic through a paracentesis port to firm up the eye. Once you've inserted the shunt, you need to confirm its position by repositioning the scleral flap and observing the device tip's location within the anterior chamber (Figure 3). If the position is satisfactory, we close the scleral flap with two interrupted 10-0 nylon sutures, and the conjunctiva with 9-0 polyglactin sutures as usual.

Figure 3: In this post-op image, the Ex-PRESS mini glaucoma shunt is in the anterior chamber, parallel to the iris plane and away from the corneal endothelium.

We use the same post-op prophylaxis regimen with the Ex-PRESS shunt as we do for trabeculectomies: a fourth-generation fluoroquinolone antibiotic, atropine and prednisolone acetate. The patient continues the prednisolone for at least 6 to 8 weeks post-op.

Technique Considerations

One of the main obstacles surgeons face with any glaucoma filtration surgery is the inability to predict how patients will respond to the procedure. When making a sclerostomy, the body's natural response is to attempt to close off and heal the opening, which is why the use of anti-metabolites has become so widespread in glaucoma surgery. These medications help delay the body's natural inflammatory healing response to the sclerostomy. Unfortunately, the healing response varies greatly among patients. For example, younger patients and those of African ancestry have a lower success rate with trabeculectomy surgery, because they tend to have a more aggressive inflammatory healing response.

One of the main benefits of the Ex-PRESS mini shunt is its fixed size. As mentioned earlier, it has an internal lumen diameter of 50 microns. This eliminates one of the variables associated with traditional trabeculectomy surgery — the size of the sclerostomy. As experienced surgeons know, it's the relationship between the size/thickness of the flap and the size of the sclerostomy that determines the ultimate filtration effect. As the size of the sclerostomy increases, a larger/thicker flap or tighter suture closure is needed to prevent postoperative hypotony from overfiltration. Similarly, with a smaller sclerostomy, a smaller flap or less tight closure is needed to prevent underfiltration and high IOP.

The size of the sclerostomy is an intraoperative variable in trabeculectomy surgery, because of interpatient differences in scleral thickness and, subsequently, in the amount of scleral tissue removed when using a punch or similar instrument. In addition, intraoperative bleeding and poor exposure may limit one's ability to determine the exact size of the sclerostomy.

However, when an Ex-PRESS shunt is inserted directly through a partial thickness sclera flap, the size of the sclerostomy will be the same every time. The scleral flap can be created and closed the same way every time, which helps to standardize the procedure somewhat. Even if the sclerostomy size with the Ex-PRESS shunt is different from what you're used to, it's at least predictable, which allows you to adjust your technique (flap size/suture tension) accordingly in order to compensate, once you have some experience with the device.

Valuable Procedure

I believe the Ex-PRESS mini glaucoma shunt placed under a scleral flap is a valuable procedure to consider in a patient deemed appropriate for trabeculectomy. It has been proven to significantly lower IOP as effectively as standard trabeculectomy, but with less risk of early, significant postoperative complications. In addition, it may lend some degree of predictability to the postoperative outcome — especially for surgeons who don't perform glaucoma filtering procedures routinely.

Although we don't have long-term follow-up data on patients who've had the Ex-PRESS mini shunts implanted (most are less than one year), our early results have been encouraging. We repeatedly have seen diffuse, posterior blebs with good IOP control. In addition, in the early post-op period, the eyes appear more quiet and stable, and patients require fewer follow-up visits.

Because of variations among individuals and in their healing responses after glaucoma-filtering surgery, some patients will experience successful outcomes while others will not. The Ex-PRESS mini shunt certainly won't change this fact. However, by increasing the standardization of the procedure and limiting tissue distortion (and subsequent inflammation and bleeding), we can increase the predictability of postoperative outcomes, thereby maximizing the chances of success. nMD