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Positive impression of iStent reinforced after 1 year of use
A surgeon explains how minor technique refinements have led to a more comfortable procedure.
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Glaucoma affects about 2.2 million Americans, and worldwide the number of suspected cases of glaucoma is estimated to be around 70 million. Although medical management has been the primary treatment modality for the most part, with an estimated worldwide annual market of more than $5 billion, this is being challenged by the new treatment approaches on the horizon of glaucoma management, especially for the large segment of glaucoma patients who fall into the categories of mild to moderate glaucoma.
Microinvasive glaucoma surgery (MIGS) is a new direction that is rapidly changing this surgical landscape. Unlike some glaucoma procedures that bypass the natural physiologic aqueous outflow, MIGS, an ab interno procedure, embraces the natural physiologic pathway in enhancing aqueous outflow and thus lowers IOP. In doing so, it also preserves ocular tissue such as the conjunctiva for possible future surgical options. Current MIGS procedures approved by the U.S. Food and Drug Administration include the iStent (Glaukos) and the Trabectome (NeoMedix). Others in the pipeline include the CyPass Micro-Stent (Transcend Medical) and the Hydrus (Ivantis), which are currently in clinical trials.
When viewing the cards of efficacy vs. safety for glaucoma surgical procedures, MIGS ranks high on safety with fewer potential postoperative complications, while trabeculectomy ranks higher than MIGS in efficacy and hence may be considered a better choice for the more advanced glaucoma subpopulation. MIGS is more for mild to moderate glaucoma patients who can have a combined cataract and glaucoma surgical procedure in one sitting. With regard to MIGS, the surgeon needs to be familiar with the anatomy of the angle to facilitate iStent and Trabectome procedures. Combining glaucoma procedures with cataract surgery seems to somewhat shift glaucoma surgery into the general ophthalmology playing field.
Newer directions of continued exploration described by others would include the use of more than one iStent and combining procedures such as in “ICE” — iStent, cataract surgery and endocyclophotocoagulation. However, from a reimbursement standpoint, only a single iStent is currently covered during cataract surgery in the U.S.
In this column, Dr. Arregui describes his continuing experience with iStent surgery.
Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor
Pablo Arregui
I published an article in Ocular Surgery News in January 2013 on my experiences as a new user of the iStent Trabecular Micro Bypass. My initial experiences were positive, albeit with a few fumbles and awkward maneuvers. More than a year later, my patients’ outcomes and my increasing comfort with the procedure have only served to reinforce my feelings that the iStent is an exciting and excellent option for patients with cataract and mild to moderate glaucoma.
Indications
The iStent device is a 1-mm-long “L-shaped” stent that is inserted into the trabecular meshwork and sits in Schlemm’s canal. It creates a patent opening to increase aqueous outflow and decrease IOP. The iStent is indicated for placement in conjunction with cataract surgery in mild to moderate glaucoma patients. If a patient is on any topical hypotensive drops or has a history of argon laser trabeculoplasty or selective laser trabeculoplasty, I recommend the procedure because I feel they will benefit from the stent. When I present it to these patients, I tell them that while we are removing their cataract, we are also going to do a procedure to help control their glaucoma. The majority of these patients I have been following and treating for many years, and they are appreciative of a potential alternative to topical glaucoma medications or a way to provide additional protection against glaucoma progression.
Results in our patients have been excellent. Most cataract surgery patients see a drop in pressure of 2 mm Hg to 3 mm Hg. When the iStent procedure is included, we are seeing an additional 2 mm Hg to 3 mm Hg drop in IOP. For patients who are on three drops or have moderate to advanced glaucoma and require cataract surgery, I perform endocyclophotocoagulation in addition to implanting the iStent.
An evolving technique
The initial online and wet lab training I received from Glaukos was excellent. Combined with a little extra practice with a gonioscope, the thorough training allowed me to be comfortable with the procedure from the start. As with all things, my technique has continued to refine over the last year. The first thing I do is raise the bed slightly higher to account for a different microscope ocular placement later in the surgery. It is minor, but being in a comfortable position relative to the patient makes the procedure a bit easier.
Following successful cataract surgery, Arregui injects Miostat to lower the pupil size and expose the angle, making light contact with the iris with the shaft of the injector to bring the pupil down more quickly.
Arregui then injects viscoelastic to expose 3 to 4 clock hours of the angle.
Images: Arregui P
Looking through the gonioprism, Arregui inserts the iStent into the angle, keeping it in the inserter momentarily to ensure it is in position.
After releasing the iStent in the angle, Arregui uses the tip of the cannula to tap the iStent to ensure it is properly seated.
Cataract surgery is performed as usual. After placing the IOL, I then place a small amount of Miostat (carbachol, Alcon) directly over the nasal iris as well as in the nasal angle to provide better access and visibility. The patient’s head is tilted 45° away from me at the same time that the microscope is tilted the same amount toward me. With the inserter in the anterior chamber and the gonioprism placed on the cornea, the inserter is then advanced across the pupil to the nasal angle to be inserted into the trabecular meshwork.
Initially, I was satisfied just to get the stent in place, even if the positioning was not perfect. I even advised other surgeons in my previous column to not “muck it up” by messing with it once it was in place. I have changed my tune a bit on that aspect. While patients still see a positive effect, when the stent is fully inserted into the trabecular meshwork it probably works a little better. If the retention ridges can be seen fairly clearly with only a translucent layer covering them, I know I have not gone deep enough into the trabecular meshwork. The ridges should be barely visible through an opaque layer of tissue.
Now that I am comfortable with the procedure, I am much more willing to grab the stent and reposition it if I feel that it is not in optimal placement. I will first try to back out and place the stent a little deeper in the same spot. If that is not quickly possible, I move to a new spot one-half to one clock hour away and insert it again.
Perhaps the most significant refinement I have made in my technique is to apply much less pressure on the trabecular meshwork. I initially failed to realize that a light touch is best, even to place the stent at the desired depth. I now just tap the trabecular meshwork with the iStent and then glide along parallel to it. Because the stent is straight and the trabecular meshwork is curved, it naturally catches and slides into location smoothly and easily. Attempting to push the stent too deep perforates the meshwork and catches the sclera, making the procedure more difficult.
Other small changes I have made include waiting to mark the cornea for astigmatism correction. When a patient is getting a toric IOL or a limbal relaxing incision during surgery, I prefer to mark the cornea after the iStent is in place. Particularly when marking between 30° and 150°, the purple ink on the cornea reflect off of the goniolens and can impede visibility. I now mark the cornea after the fact.
At the end of the case, I leave the eye slightly “firm.” By elevating the eye pressure at the end of the case, this helps diminish the amount of blood that may ooze from the iStent site. This deceases the likelihood of a microhyphema in the early postoperative period.
Latest reflections
The refinements to my technique over the last year have been minor overall but contribute to a more comfortable procedure that allows me to have greater confidence. Patients who move frequently due to breathing problems or those who have narrow angles or a floppy iris are more demanding, and I might have avoided performing the procedure on them at first. I now have no difficulty with placing the iStent in these patients. New modifications to the gonioprism combine it with a Thornton ring, making it easier to manipulate the eye and simultaneously see the angle. Overall, I thoroughly enjoy this procedure. It is satisfying as a surgeon to perform, and my patients are pleased with the outcomes.