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Trabecular micro bypass stent allows simultaneous treatment of glaucoma during cataract surgery
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Combined glaucoma and cataract surgery at one sitting can be beneficial to patients, reducing the need for a second surgical procedure and decreasing the overall cost of these procedures. However, in the past, these combined procedures were more involved for both cataract extraction and glaucoma surgery, and in many cases, glaucoma specialists were involved.
With the commencement of the new era of microinvasive glaucoma surgery (MIGS), the amalgamation of phacoemulsification with MIGS has become a reality. Further, it is well-established that phacoemulsification has a beneficial effect in patients with open-angle glaucoma, resulting in a sustained IOP reduction of about 1.5 mm Hg; this reduction can be greater in patients with a higher preoperative pressure reading. But when phacoemulsification is performed in an eye with a pre-existing bleb from a trabeculectomy, it can have a somewhat deleterious effect on the bleb function, often resulting in an IOP rise of about 2 mm Hg after 1 year.
Newer surgical options, such as the iStent (Glaukos) and Trabectome (NeoMedix), both approved by the U.S. Food and Drug Administration, when performed with phacoemulsification, can decrease IOP up to about 5 mm Hg. On the horizon are other choices not available to clinicians, namely CyPass (Transcend Medical) and Hydrus (Ivantis), both not FDA approved, that can be combined with phacoemulsification and may result in a greater IOP-lowering effect, but the final long-term results are yet to be known. Other options include combining FDA-approved canaloplasty with a tension suture and phacoemulsification, which can provide an IOP lowering of about 8 mm Hg to 10 mm Hg. These newer additions in the glaucoma surgical armamentarium allow the combined management of cataract and open-angle glaucoma without having a high complication rate. Hence, the current combined phacoemulsification-glaucoma surgery scene looks good, and the future looks promising and even brighter.
In this column, Dr. Shingleton describes his technique for iStent trabecular micro bypass surgery.
Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor
Bradford J. Shingleton
The treatment paradigm for glaucoma is changing with the development of microinvasive glaucoma surgery. Historically, mild to moderate glaucoma has been primarily treated with topical medications, which have marginal patient compliance rates. However, surgical therapy outcomes can be uncertain and negatively interfere with cataract surgery, a frequent comorbidity. The iStent trabecular micro bypass, the first MIGS device to gain FDA approval, allows surgeons the possibility of effectively treating open-angle glaucoma simultaneously with cataract, without negatively affecting the outcomes of the cataract procedure.
Surgical protocol
The iStent is placed once the IOL is in place, utilizing the same incisions. After the standard cataract operation, I inject carbachol into the anterior chamber to bring down the pupil, followed by placement of OcuCoat (2% hydroxypropyl methylcellulose, Bausch + Lomb) on the surface of the cornea to maximize clarity, because good visualization is critical for the iStent procedure. I then place a temporary 10-0 nylon suture in the keratome incision and in the paracentesis incision to make sure the seal is as watertight as possible.
I prefer a relatively firm eye — not rock hard but not soft — because a firmer eye allows better visualization with the gonioprism; thus, I fill the anterior chamber again with viscoelastic to further deepen the angle. At this point, I tilt the patient’s head approximately 30° away from me. The microscope is also tilted to allow a clear view into the nasal angle. I use a gonioprism, coated with viscoelastic on the corneal side, to visualize the trabecular meshwork and determine if it is best to place a right-hand stent with a backhand approach or a left-hand stent with a forehand approach. Either is fine; I select the one that is the most suitable for a given patient.
The microscope is set for moderate to high magnification, making sure that the focus is crystal clear. Holding the inserter as you would a pencil, with the index finger on the front, I pass the iStent inserter across the anterior chamber and approach the trabecular meshwork at a slight angle, approximately 15°. Once I engage the trabecular meshwork and Schlemm’s canal with the stent, I flatten the approach so that the stent is nearly parallel to the canal. I then pull back very gently toward me before sliding the iStent in place.
The surgeon delivers the iStent through the anterior chamber as viewed through the gonioprism.
Images: Shingleton BJ
The iStent is inserted into the trabecular meshwork.
After placing the iStent into proper position, the surgeon releases the implant by gently rolling back his index finger.
After implanting, the surgeon taps the iStent to ensure it is properly seated and at the proper angle in the trabecular meshwork.
Placement of the iStent is complete.
The stent should enter Schlemm’s canal with minimal resistance. If resistance is encountered, it is generally due to engaging the posterior wall of the canal, and this will cause the eye to rotate. By flattening my approach after engaging the iStent and then pulling back slightly, I avoid this potential problem. To release the stent from the inserter, I gently roll my index finger back. Once the iStent is released, I tap it to make sure it is in good position, not angled or tilted, and in the majority of cases, that completes placement. If I am not pleased with the placement, I re-engage the stent with the inserter and relocate it to another site. That is uncommon, but I think all surgeons should be prepared for that possibility. I find that the inserter allows me to pick up the stent fairly easily if it is not in its proper place.
I then aspirate the viscoelastic from the eye and deepen the chamber with balanced salt solution so that I can check the stability of the stent with the gonioscope. A small amount of reflux from Schlemm’s canal is a common occurrence and indicates that the stent has been placed properly.
Once I am confident the stent is in place, I reposition the patient’s head, take out the 10-0 nylon sutures, and deepen the chamber once again with balanced salt solution to confirm the incisions are watertight. Because I have already injected carbachol, I finalize the procedure with application of topical prednisolone acetate 1%, a beta blocker, and a topical alpha agonist, if not contraindicated. Postoperative care is the same as with any cataract patient; I see the patient the first day after surgery and check the stent with the gonioscope.
The technical skill required for placing the iStent is within the purview of a comprehensive ophthalmologist. The aforementioned steps will assist the surgeon in optimizing visualization and success with the procedure.