Details on how I perform this procedure.
I have been using the EX-PRESS Glaucoma Filtration Device (Alcon Laboratories, Inc., Fort Worth, TX) (Figure 1) for more than 4 years now as an advancement over trabeculectomy. Many glaucoma surgeons are already familiar with this device and know that it refines trabeculectomy and promotes consistency. This article describes my step-by-step technique for using this device to the best advantage.
First, I think it is critical to identify landmarks for placing the EX-PRESS device correctly. Landmarks may not be as critical as in a canaloplasty, but they certainly deserve attention in this procedure. I do this before making any incisions or entering the anterior chamber. I like to assess the important landmarks throughout the case, not just when I have the EX-PRESS glaucoma device in my hand. To help me identify landmarks before I create the scleral flap, I look for a randomized pattern of scleral fibers posteriorly. At the scleral spur, I see a white, glistening band of fibers that crosses the bed of this section. The blue zone is a transition zone to the clear cornea. I want to make sure that I implant the EX-PRESS device in the anterior chamber, just at the level of the scleral spur, but not too far posteriorly (Figure 2). It is important for the device to enter the eye exactly at the anterior aspect of the scleral spur and for it to remain at the iris plane so that it does not point downward toward the iris (Figure 3).
Positioning and Sizing the Scleral Flap
After I make my conjunctival opening, I create a fornix-based flap. I like to look at the sclera and visualize the location of the blue zone and the scleral spur, estimating where my entry point for the EX-PRESS device will be. My fellows will often place a small ink spot there to remember exactly where to position the implant so that they can build a flap around that area (Figure 4). A trabeculectomy flap can be large or small, but not so small that it does not cover the implant. The external plate of the EX-PRESS device is 1 x 1 mm, so I make these flaps 4 x 3 mm so there is enough tissue to overlap the implant laterally and posteriorly to resist aqueous flow (Figure 5). Personally, I do not like to make the flap overly large; it is unnecessary and may push down onto the external plate of the device excessively. Then, I advance the flap into the clear cornea so there is a small gap between it and the implant that prevents the flap from pushing down on the device.
The thickness of the scleral flap is just as important with the EX-PRESS Glaucoma Filtration Device as it is during standard trabeculectomy. I prefer to make these flaps 0.50 to 0.75 mm thick. To make the entry point into the anterior chamber, I find both sapphire blades and hypodermic needles useful. I use a 27-gauge needle for the majority of my cases. Again, the entry point should be anterior to the scleral spur. It may take some time to get used to operating with the eye turned down, but this position helps the surgeon enter the sclera perpendicular to the iris; otherwise, the entry point may face the iris. If placed incorrectly, the implant may pinch the iris. Of course, I also make sure to place the EX-PRESS device at a safe distance from the cornea. It is important to differentiate between the entry point (based on external scleral landmarks) and the entry plane (based on the iris plane).
To insert the EX-PRESS Glaucoma Filtration Device, I rotate it 90° so that it enters the eye with the spur facing the long axis of the entry point (Figure 6). I rotate the device to its final position once it is inside the eye. Figure 7 shows the perfect positioning of the implant in the anterior chamber, and Figure 8 shows how the external back plate must be flush with the scleral bed before the flap is closed. There have been some issues in the past when the back plate is not placed properly.
Surgeons can use their preferred trabeculectomy technique for the EX-PRESS Glaucoma Filtration Device. I usually administer topical anesthesia (lidocaine). I prefer to use a fornix-based flap, but I leave a conjunctival stump to suture the conjunctiva closed. I use a blunt spread of the conjunctiva and Tenon’s capsule into the quadrant to avoid some of the blood vessels. I like to use diamond blades, although metal blades are certainly a reasonable choice. I personally do not use set-depth blades, however; I prefer to make the cuts freehand so I can visualize their depth. I may advance the blade deeper than I need to posteriorly so I can gauge the sclera’s thickness, and then I will retract the blade slightly to perform the lamellar dissection. I like to use the tunnel technique to make the scleral flap, because I think it leaves the scleral bed smoother.
I do not dissect the scleral flap as anteriorly as I perform a trabeculectomy dissection. It is not necessary to dissect too far into clear cornea, as the device’s entry point will not be in the cornea. Nevertheless, it is important to dissect at least past the area of the blue zone to create enough space to accommodate the implant. Before inserting the EX-PRESS device, I make sure I can visualize the scleral spur and the blue zone. I then apply a wound-management technique before making my entry point.
Although the EX-PRESS procedure is a penetrating procedure, I do not fill the eye with viscoelastic, because it stays quite formed, even after I enter the anterior chamber. I introduce the knife just at the anterior aspect of the scleral spur. Again, it is important to carefully place the device at the iris plane. When the applicator is in place, I simply push down to release the device. The entry point for the device is narrower at the vertical meridian and wider in the horizontal meridian. If necessary, I can turn the implant 90° to position it correctly. Some striation often occurs, but the tissue will push the device in because of the spur. I like a tight fit of the EX-PRESS device into the incision in the eye—large enough to insert with excessive trauma and stretching of tissue, but not so large to cause excessive leakage from around the device. Some egress of aqueous will be visible when the implant is in place.
Closing the Scleral Flap
Although some surgeons do not place any sutures in the scleral flap, I feel more comfortable doing so to create some resistance to flow. I use an intraoperative gonio mirror to make sure I have placed the device in the correct plane and position. Sometimes, in eyes with a very deep anterior chamber, such as highly myopic eyes, it can be difficult to see the implant in the peripheral anterior chamber (hence the use of a mirror to identify it). To dynamically check the flow, I continuously inject BSS solution (Alcon Laboratories, Inc.) into the area. I place two standard slipknots that I typically use for trabeculectomy (two single throws in the same direction), which allows me to tighten or loosen the scleral flap after assessing the flow. I may not be as obsessive about the amount of flow as I am with trabeculectomy, but I do want to make sure the chamber is maintained and that there is some resistance to flow. Finally, I lock the sutures so that the flap is closed. I use a running horizontal mattress suture to close the conjunctiva to itself in a watertight fashion.
The most important steps of implanting the EX-PRESS Glaucoma Filtration Device are to (1) identify the landmarks, (2) size and locate the scleral flap appropriately, (3) make the entry point at the anterior spur and the entry plane at the iris plane, and (4) close the flap to permit some additional resistance. I feel that the EX-PRESS device represents a nice advancement from standard trabeculectomy.
Iqbal “Ike” K. Ahmed, MD, FRCSC, is an assistant professor at the University of Toronto and a clinical assistant professor at the University of Utah in Salt Lake City. He is a paid consultant for Alcon Laboratories, Inc. Dr. Ahmed may be reached at (905) 820-3937; email@example.com.
To read the EX-PRESS Glaucoma Filtration Device directions for use and important safety information, click here.