The iStent (Glaukos), one of the newer options for minimally invasive glaucoma surgery, has become increasingly popular for my glaucoma patients who concurrently suffer from visually significant cataracts. Unlike the Trabectome (Neomedix), which can be performed as a stand-alone procedure, the iStent is only approved for combined cataract and early to moderate open-angle glaucoma.This 1mm titanium implant, which resembles a snorkel, is the smallest FDA-approved device to be put into the human body. Conceptually similar to a cardiac stent, the iStent serves as a bypass through the trabecular meshwork to improve aqueous outflow. Clinical results up to two years post-implantation show a 20% to 33% decrease in IOP from baseline. This procedure is a great option for patients ready to have cataract surgery who also have early to moderate open-angle glaucoma. Ideal candidates are those already on one to three glaucoma drugs, whose IOP targets are in the mid-teen range, have compliance issues and/or want to decrease the burden of drops for managing their glaucoma.
My ApproachPrior to the cataract extraction, proper head positioning is performed and an adequate view of the angle anatomy with a gonio lens is confirmed. I will then make a 1.4mm temporal corneal incision with a 15-degree blade, then I fill the anterior chamber with viscoelastic. The iStent inserter is advanced across the anterior chamber and, with the magnified view of a gonioprism, the iStent is then implanted through the trabecular meshwork and secured into Schlemm’s canal. There is typically an egress of heme from Schlemm’s canal, indicating proper placement. Once completed, I will proceed to my cataract extraction and IOL implantation. At the end of the surgery, the corneal wounds are hydrated for a watertight seal as would be performed in cataract surgery alone; typically, no sutures are necessary.
Pros and ConsThis procedure has several advantages. First, when compared to traditional glaucoma surgical procedures, it’s minimally invasive, with a faster operative time, more rapid healing and fewer complications. There is no penetration or disturbance of the conjunctiva, allowing for future conventional glaucoma surgeries if needed. Since the site of surgery is ab interno, there is no astigmatic change, no bleb to cause ocular surface irritation or a chronic surgical site to pose a life-long risk of infection. Also, the procedure is contact lens wearer-friendly. That said, this procedure does have some disadvantages. The iStent indication is limited to implantation in combination with cataract surgery, as opposed to a stand-alone procedure. Although the implant is very small, placing a foreign object into the eye does introduce the potential risk of intraoperative complications, e.g., if the device is malpositioned and the tip becomes occluded by iris or if the device becomes dislodged. Postoperatively, there can be IOP spikes and hyphema. Also, because it is a fairly new procedure, it is considered experimental and not currently covered by many commercial insurances, although it does have excellent Medicare coverage. Preoperatively, candidates require a full glaucoma and cataract work up with ancillary testing (pachymetry, visual field, RNFL analysis, K readings, axial length, etc.). Blood thinners should be stopped preoperatively if possible. Post-op care is the same as traditional cataract surgery. Patients should be informed that their vision may be blurred for the first few days due to the mild bleeding during the surgery.
Dr. Okeke is a glaucoma specialist at Virginia Eye Consultants and an assistant professor at Eastern Virginia Medical School.