PRODUCT DETAILS
The Ex-PRESS mini glaucoma shunt is constructed of implantable, biocompatible stainless steel approved for human use (Figure 1). It is 2.96 mm long and has an outer diameter of 400 µm. The lumen size of the product (R-50) available in the US is 50 µm. The shunt's penetrating tip is blunt and needle-shaped in order to minimize tissue damage and facilitate insertion. While the distal end has a flat, angled flange to prevent intrusion and blend with the limbal anatomy, the proximal end has a beveled spur to prevent extrusion, and the distance between the spur and the shunt's distal flange equals the scleral thickness. The angles of the disc and spur are designed to follow the normal anatomy of the limbal area. The shunt's proximal end also features three additional transverse orifices to prevent plugging by the iris, blood, or inflammatory membranes. The device comes loaded on a disposable inserter.
Figure 1. The penetrating tip of the Ex-PRESS mini glaucoma shunt is blunt and needle-shaped in order to cause minimal tissue damage and facilitate insertion
The concept of the Ex-PRESS mini glaucoma shunt is similar to that of trabeculectomy; both divert aqueous humor from the anterior chamber to the subconjunctival space. The patented flow-restricting unit inside the shunt's lumen, however, provides a fixed resistance to flow. The shunt is sterilized with gamma irradiation. In a pretrial study conducted by Optonol, magnetic exposure did not affect the Ex-PRESS mini glaucoma shunt. The study's results confirmed that patients implanted with the shunt are at no additional risk when undergoing MRI procedures, but it is advisable to avoid an MRI of the head in the first 2 weeks after surgery.
INDICATIONS
The Ex-PRESS mini glaucoma shunt is an option in all instances in which the surgeon would normally first elect to perform a trabeculectomy, but it is not a substitute for Seton procedures. The device's applications include primary open-angle glaucoma, pseudoexfoliative glaucoma, aphakic or pseudophakic glaucoma, and combined cataract and glaucoma procedures. The shunt is unsuitable for patients with narrow angles, extensive perilimbal conjunctival fibrosis, opaque corneas, uveitis, ocular infection, severe dry eye, and severe blepharitis.
SURGICAL TECHNIQUES AND POSTOPERATIVE MANAGEMENT
The implantation procedure may be performed using local or topical anesthesia. The eye is prepared and draped using conventional sterile procedures. After pulling the eye down with a retraction suture, the surgeon creates a small 2- to 4-mm circumferential incision on the conjunctiva approximately 8 mm away from the limbus. He uses a cotton-tipped applicator or a pair of Westcott scissors to undermine the Tenon's capsule up to the limbus. In high-risk cases, the surgeon may use an antimetabolite at this point in the procedure.
After filling the anterior chamber with a viscoelastic material via a temporal clear corneal paracentesis, the surgeon slides a 26-gauge needle under the conjunctiva onto the limbus and enters the anterior chamber while keeping the needle parallel to the iris. Next, the surgeon inserts the Ex-PRESS mini glaucoma shunt through the needle-created track with the aid of the introducer. He should again fill the anterior chamber with viscoelastic material to prevent its shallowing postoperatively. The surgeon may also inject the viscoelastic under the conjunctiva after its closure for an additional tamponade effect. The idea is to prevent overfiltration and hypotony. The ideal position of the shunt is shown in Figure 2.
Figure 2. The shunt is shown in its ideal position.
The shape of the anterior chamber, the IOP, and the presence of inflammation dictate postoperative medications, and care of patients following surgery resembles that of trabeculectomy. Complete wound healing may last 3 to 4 weeks.
RESULTS
An open-label, multicenter study1 conducted at 14 international sites in eight countries enrolled a total of 113 patients with primary open-angle glaucoma into three protocols. The first protocol involved 56 patients with failed medical therapy or trabeculoplasty. The second comprised 36 patients with failed medical therapy or laser trabeculoplasty who underwent combined cataract surgery and implantation of the Ex-PRESS mini glaucoma shunt. The third protocol consisted of 21 patients who had prior failed trabeculotomy surgeries. The follow-up period was 1 year.
At 1 year postoperatively, the mean IOP reduction was 33.8% (Figure 3), and the average number of glaucoma medications prescribed dropped significantly from 1.55 preoperatively to 0.52. The cumulative probability of success for version R-50 at 1 year was 79%.
Figure 3. A multicenter study demonstrated these dynamics of IOP after insertion of the Ex-PRESS mini glaucoma shunt. (*preoperatively / **day 1 postoperatively)
My personal experience since November 2002 consists of eight eyes of seven patients. At 8 weeks, the average reduction of IOP was 40%. One eye developed a shallow anterior chamber that resolved after viscoelastic injection.
COMPLICATIONS
Hypotony (an IOP of less than 5 mm Hg) in the first few days may be encountered in 63.6% of patients. All cases resolve by 1 month. Other complications may include choroidal detachment (0% to 7%); suprachoroidal hemorrhage (0% to 4%); shallow anterior chamber (0% to 6%); flat anterior chamber (0% to 2%); and anterior chamber reformation (0% to 3%).1 All of the complications described here may be dealt with accordingly.
There are some complications specific to the Ex-PRESS mini glaucoma shunt. Mechanical erosion of the conjunctiva at the plate occurs in 2% to 7% of patients. To avoid erosion, one may wish to refrain from implanting the device in patients with thin conjunctiva and to insist on optimal positioning during surgery. Conjunctival erosion requires either removal of the shunt or covering the defect with healthy conjunctiva.
An encysted bleb may occur in 28.4% of patients when no antimetabolites are used; in high-risk patients, intraoperative antimetabolites may prevent excessive scarring. The problem is treated by needling or 5-fluorouracil injections.
Surgeons may consider explanting the shunt when it is incorrectly placed or when no filtration is seen through it and the patient requires further filtration surgery. Explantation involves performing a scleral incision at the device site and enlarging it laterally. The surgeon then grasps the unit with a serrated forceps and rotates the shunt until the spur is parallel to the scleral incision. Next, he gently withdraws the device and sutures the conjunctival and scleral holes.
CONCLUSION
There are several advantages associated with the Ex-PRESS mini glaucoma shunt as compared with trabeculectomy. Its small size requires minimal manipulation of tissues, and its implantation procedure is rapid and reversible. There is no need for an iridectomy, and postoperative inflammation is minimal. As with a full-thickness filtration procedure, implanting the shunt may cause initial hypotony. The restriction of flow through the tube and the use of viscoelastic materials may prevent this complication, however.
Karanjit S. Kooner, MD, MBA, is an associate professor at the Department of Ophthalmology, UT Southwestern Medical Center. He holds no financial interest in the product mentioned herein. Dr. Kooner may be reached at (214) 648-4733; kjkooner@yahoo.com.
1. CIBA Vision. Surgical solutions: Ex-PRESS mini glaucoma shunt. Available at: http://www.cibavision.com/products/surgical_solutions/Ex-PRESS.shtml. Accessed January 28, 2003.
