A New Glaucoma Device With Potential

Thomas W. Samuelson, MD

Why I changed my tune about the EX-PRESS Glaucoma Filtration Device.
By Thomas W. Samuelson, MD

New options make this an exciting time to be a glaucoma surgeon. This article describes my experience with the EX-PRESS Glaucoma Filtration Device (Alcon Laboratories, Inc., Fort Worth, TX). I refer to the use of this device as the EX-PRESS-assisted guarded filtration procedure, which I believe is more refined and standardized than traditional trabeculectomy. In 2002, when the EX-PRESS Glaucoma Filtration Device first became available as an unguarded subconjunctival procedure, I called it “glaucoma roulette,” because I worried that its lack of a barrier to filtration would induce hypotony. The device’s 50-µm lumen offers some resistance to aqueous flow, but I did not feel it was enough to act as the sole resistor to flow. As such, I did not incorporate the EX-PRESS device into my practice at that time. Once the EX-PRESS device was modified for use under the scleral flap, I decided to try it in my patients, and I have been using the EX-PRESS device-assisted guarded filtration procedure since then with increasing frequency.

Minimally Invasive

I currently perform fewer transcleral filtration procedures than I have in the past, due to the fact that I have adopted the less invasive “bleb-less” procedures for patients with early-to-moderate glaucoma. However, I like to use the EX-PRESS glaucoma device in eyes in which it is necessary to abandon the trabecular meshwork and perform a transscleral procedure. I like the EX-PRESS device because it is minimally invasive. It requires a very small point of entry into the anterior chamber (I insert the P-50 model through a 25-gauge needle tract) (Figure 1A and B). Such a minimally invasive approach has many advantages. The device’s placement does not shallow the anterior chamber, and the eye maintains pressures close to physiological throughout the procedure. The P-50 model of the EX-PRESS device has a notch in the back that helps direct aqueous flow posteriorly. The EX-PRESS device-assisted guarded filtration procedure carries no risk of iris prolapse or bleeding from the ciliary body, unlike traditional trabeculectomy. The device also permits a much more elegant and standardized sclerostomy. Some glaucoma surgeons may feel that they do not need help making a hole in the eye, but it is challenging to make a sclerostomy that is the same dimensions every time. The EX-PRESS device does not eliminate or substantially reduce surgical expertise required for the remaining portions of the guarded filtration procedure.

Fig.1

Figure 1. The author creates a 60%-depth partial-thickness, trapezoidal scleral flap (approximately 3.5 mm based at the limbus) (A). The EX-PRESS Glaucoma Filtration Device P-50 has a notch to facilitate posterior flow.

EX-PRESS Implantation Technique

Creating the Scleral Flap
To make the scleral flap, I create a small peritomy at the 12:00 o’clock position and inject lidocaine. I often use epinephrine with the lidocaine (1% or 2%) when injecting anteriorly in order to blanche the blood vessels. I tend to leave a small rim of limbal conjunctiva to assist with the conjunctival closure (although I do not incorporate this rim of tissue into the closure). I then utilize a wound-management technique in the effort to create a successful bleb. I typically use either a diamond knife or a #75 supersharp blade to make the 2/3-thickness groove for the scleral flap before completing the flap with a #67 blade. I carefully make sure I am on a smooth plane when dissecting the scleral flap. It is important not to create a multiplane dissection for the EXPRESS device, because the region within the deeper plane can dehisce under the pressure of the insertion if the bed tissue plane is too thin. The key to avoiding this error is making the dissection of the plane as smooth as possible. When using the EX-PRESS device, it is important that each component of the dissection (the flap and the bed) are of appropriate thickness. A thin scleral flap may allow the device to erode through the flap, whereas a thin bed may tear during the device’s insertion. The flap should be 1/2 to 2/3 of the scleral thickness. Although some surgeons prefer to use a guarded preset knife, I do not, because I think scleral thickness varies from eye to eye.

Placing the Device
The entry point for the EX-PRESS Glaucoma Filtration Device is critical to success. I preplace two 10-0 nylon flap sutures (a technique I learned from Garry Condon, MD), which adds control to the procedure without any drawbacks. I then enter the anterior chamber with the 25-gauge needle (Figure 2) and position the tip of the device in the needle tract. Up until this point, my second hand is retracting the scleral flap. While actually inserting the EX-PRESS device, however, I prefer to fixate the eye by grasping the margin of the scleral bed rather than the flap. I fear that the pressure needed to push the spur of the device through the incision may be enough to tear a thin flap if the sceral flap itself is used to stabilize the eye during this step. I gently push the device into place until I feel a pop. I keep my finger on the ridge of the insertion device so I do not have to fumble around to find it when I am ready to release the EX-PRESS device from the inserter.

Fig.2

Figure 2. The EX-PRESS filtration device facilitates placement of the P-50 device through a 2- guage needle tract.

Suturing the Flap
Having the sutures already in place makes the closing the wound much easier. I test the flow of aqueous through the device before suturing, but I do not perform titration of flow at this point. I always perform a careful closure of the scleral flap, utilizing at least two sutures. I would caution surgeons not to skip this step. There are no disadvantages to titration of flow with sutures. I either cut the sutures with the laser or use releasable sutures. I advocate using the scleral flap as a resister rather than simply relying on the device to provide all of the resistance to flow.

Discussion

What I really like about the EX-PRESS Glaucoma Filtration Device is its potential to facilitate glaucoma surgery in myriad ways. Andre Mermoud, MD, has described the use of the EX-PRESS device to facilitate a posterior deep sclerectomy.1 He implants the EX-PRESS device and directs the aqueous flow posteriorly to a deep scleral cut down where the uveal tissue has been exposed. He then closes the scleral flap tightly to encourage subscleral outflow. Unlike the trabeculo-descemet’s window of viscocanalostomy, having an EX-PRESS device in the anterior chamber promotes a predictable flow in such procedures. This novel approach is just one other way that creative surgeons are using the EX-PRESS device to perform less invasive surgery. I am excited to have this device available, and I anticipate that glaucoma surgeons will continue to find additional uses for it. Also, it appears to be safe for MRI scanning,2 a question that radiologists often ask. The only negative aspect of the EX-PRESS device is that it adds expense to the trabeculectomy procedure.

Finally, surgeons new to the EX-PRESS device may need to slightly alter their postoperative strategy. For example, a filter utilizing the EX-PRESS device is less responsive to focal massage in the early postoperative period. I have to apply diffuse pressure to the globe to increase the IOP and push the fluid through the device. In addition, I tend to cut sutures earlier when I use the EX-PRESS device. I would like to see data that the EX-PRESS device poses no longterm risk for the corneal endothelium. Again, I now implant the EX-PRESS device the majority of the time, rather than perform my standard trabeculectomy procedure, and I get excellent results.

Thomas W. Samuelson, MD, is an adjunct associate professor at the University of Minnesota in Minneapolis and an attending surgeon at Minnesota Eye Consultants/Phillips Eye Institute in Minneapolis. He is a consultant to and investigator for iScience Interventional, Glaukos Corp., GMP Companies, Inc. AquaSys, Ivantis, Alcon Laboratories, Inc., and Abbott Medical Optics Inc. Dr. Samuelson may be reached at (612) 813-3628; twsamuelson@mneye.com.

  1. Deep sclerectomy still a viable and effective procedure,results show.OSNSupersite. http://www.osnsupersite.com/view.aspx?rid=42774.Septmber 1,2009. Accessed May 17,2010.
  2. Geffen N,Trope GE,Alasbali T,et al.Is the EX-PRESS glaucoma device magnetic resonance imaging safe? J Glaucoma. 2010;19(2):116-118.

To read the EX-PRESS Glaucoma Filtration Device directions for use and important safety information, click here.