iStent inject W offers better results than earlier-generation devices
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Patients with primary open-angle glaucoma who undergo cataract surgery have an opportunity to have both phacoemulsification with IOL implantation and a glaucoma procedure performed at the same sitting.
This negates the need for a second visit to the operating room to perform a separate glaucoma surgical procedure.
This combined procedure provides the benefit of improving vision and decreasing IOP postoperatively, which can translate to less or no need for glaucoma drops, depending on the surgical result. When performing an iStent procedure (Glaukos), some areas of focus include good visualization of the angle and trabecular meshwork for optimal positioning of the device. Patients with glaucoma and cataract should be considered for this combined procedure due to its relative ease and potential benefits.
In this article, Dr. Hengerer describes the preoperative assessment and surgical procedure of an iStent inject W in a step-by-step manner with intraoperative images.
Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor
A 64-year-old man who was diagnosed 10 years ago with primary open-angle glaucoma presented for cataract surgery.
He was on two IOP-lowering medications, Xalatan (latanoprost, Pfizer) and Trusopt (dorzolamide, Merck). We had previously tried a beta-blocker and found that he was allergic to this medication class; he also had undergone selective laser trabeculoplasty in 2016. On two drops, the patient’s IOP was 25 mm Hg in the right eye and 24 mm Hg in the left eye, and I thought he would benefit from a MIGS procedure to further reduce the pressure.
This myopic patient had a nice, deep chamber (3.66 mm in the right eye and 3.62 mm in the left eye) and a wide angle (Shaffer angle grade 3 to 4; 39° in the right eye, 33° in the left eye with the Oculus Pentacam HR), making him a good candidate for an ab interno canal-based MIGS procedure to restore physiological outflow. Scars from the previous SLT were visible at every clock hour, and the trabecular meshwork was only partially pigmented.
I operated on both eyes, a few days apart, under topical anesthesia. In both eyes, implantation of two trabecular micro-bypass stents (iStent inject W, Glaukos) could be performed safely. This is a new CE-marked MIGS device that is built on a familiar platform. Compared with the earlier-generation iStent inject, the flange at the base of the iStent inject W is much wider (360 µm vs. 230 µm in diameter), which helps to enhance visibility and facilitate implantation for increased procedural predictability. Otherwise, the body of the stent and the side flow outlets are exactly the same.
With this procedure, it is important to sit on the temporal side so that you can tilt both the microscope and the patient’s head to provide a good view of the chamber angle to accurately place the stents in the nasal inferior and nasal superior areas of Schlemm’s canal.
After IOL placement, I like to deepen the chamber angle on the nasal side with a medium-viscosity ophthalmic viscosurgical device (OVD). Use a cohesive viscoelastic such as Healon/Healon GV (Johnson & Johnson Vision), ProVisc (Alcon) or Amvisc (Bausch + Lomb) and ensure that the eye is well pressurized before attempting the iStent inject W procedure. You can also use a miotic in advance to bring the pupil down; this will further open the angle for a better view.
I hold the gonioprism in my left hand and cover the cornea with dispersive OVD to achieve a clear, bright view of all the internal structures (Figure 1). It is important to use a light touch with the gonioprism. Too much pressure on the eye can cause viscoelastic egress from the wound, resulting in flattening of the anterior chamber or corneal folds that impede visualization. To more easily view the trabecular meshwork, I increase my microscope magnification to 10 to 12 times and focus on the target implantation site in the center of the trabecular meshwork, ensuring adequate illumination of up to 75% to 85%.
Source: Fritz H. Hengerer, MD
I insert the injector through the main incision on the temporal side without retracting the insertion sleeve. I traverse through the eye, being careful not to touch the cornea. Once I cross the pupillary margin, I retract the micro-insertion sleeve to view the trocar and then proceed forward, focusing on the pigmented area of the trabecular meshwork. In this case, because there was not good trabecular meshwork pigment, I used the dimple technique (Figure 2). I approached perpendicular to Schlemm’s canal, passing the trabecular meshwork, and lightly pressed the trocar against the sclera, “dimpling” it. After a second or so, you can deploy the first stent. With this technique, the blood reflux from the stent will typically be a little delayed, as the pressure used to create the dimple temporarily empties Schlemm’s canal. Once it has refilled, you will see the blood reflux.
I placed the stents at 3 o’clock and 5 o’clock in the right eye and 9 o’clock and 7 o’clock in the left eye (Figure 3). After placing the second stent, I withdraw the injector straight back from the eye and carefully flush all the viscoelastic from the eye. Blood reflux indicates correct positioning.
During the immediate postoperative period, this patient experienced a steroid response, with elevated IOP in the 22 mm Hg to 23 mm Hg range for about 6 weeks. At 3 months, the stents were well positioned, and IOP had come down to 14 mm Hg to 15 mm Hg. By 14 months, his IOP was 10 mm Hg in both eyes, and the patient was no longer using any IOP-lowering drops. This is a surprisingly good result — better than we have seen with previous generations of the iStent. The patient was happy to be off topical drops, and I was pleased with the large reduction in IOP compared with preoperative levels.
- For more information:
- Fritz H. Hengerer, MD, can be reached at Bürgerhospital Frankfurt, Nibelungenallee 37, 60318 Frankfurt am Main, Germany; email: f.hengerer@buergerhospital-ffm.de.
- Edited by Thomas “TJ” John, MD, a clinical associate professor at Loyola University Chicago and in private practice in Oak Brook, Tinley Park and Oak Lawn, Illinois. He can be reached at email: tjcornea@gmail.com.
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