This article is more than 5 years old. Information may no longer be current.
Tips and tricks to ease implantation of the iStent
P. Dee Stephenson, MD, FACS, ABES, FSEE, and Cathleen M. McCabe, MD, explain how they have modified their techniques as they gained experience with the device.
Click Here to Manage Email Alerts
Welcome to another edition of CEDARS/ASPENS Debates. CEDARS/ASPENS is a joint society of cornea, cataract and refractive surgery specialists, here to discuss some of the latest hot topics in ophthalmology.
Minimally invasive glaucoma surgery (MIGS) has received much attention over the past year. With an aging population and growing incidence of glaucoma, the ability to treat this condition with a powerful yet lower-risk therapy has become of paramount importance. This month, P. Dee Stephenson, MD, FACS, ABES, FSEE, and Cathleen M. McCabe, MD, discuss their methods of implementing MIGS into their practices. We hope you enjoy the discussion.
Kenneth A. Beckman, MD, FACS
OSN CEDARS/ASPENS Debates Editor
iStent techniques and pearls
I have now been doing MIGS surgery with the iStent (Glaukos) for about 1 year. There are techniques and pearls that come with experience and seeing enough cases so that you can give advice to others starting out. I have modified my technique several times by listening to others and utilizing new instrumentation.
Anatomy
Know how to use the gonioprism, and know your landmarks. Remember, all eyes vary, and in diabetic eyes, the anatomy is like tissue paper. If the stent is not placed on the first attempt, sometimes it is very hard to place it at all.
Positioning
There is one thing I do that is a little different. I am a microincision cataract surgeon who uses a 12 o’clock primary incision. So instead of turning the patient’s head to the left or right and making another incision, I place the bed in reverse Trendelenburg and have the patient put his chin down. Then I adjust the microscope. I have found this to work nicely because it allows my hands to be in my normal operating position.
New instrumentation
I use the 25-gauge MST micro-forceps to place the stent instead of the current injector. The injector is improved from the first version, but if I ever have to regrasp or retrieve the stent, these forceps make it easy. I reload the stent with the MST forceps before even attempting the insertion because it is just easier.
Figures 1 and 2. A 25-gauge MVR blade is used to bisect the trabecular meshwork for about 1 clock hour, similar to a goniotomy. This opens the canal like a landing strip before placement of the iStent.
Images: Stephenson PD
Figures 3 and 4. After firming up the eye with balanced salt solution through paracentesis, there will be blanching of the vessels in the area of the stent, indicating that it is placed correctly, due to the flow through the stent into Schlemm’s canal.
Another technique
I have also tried using a 25-gauge MVR blade to bisect the trabecular meshwork for about 1 clock hour, similar to a goniotomy. This opens the canal like a landing strip. I then place the iStent, which has been helpful in difficult cases (Figures 1 and 2).
Correct placement
I also think it is important to make sure that the iStent is in the proper position and working correctly. After placement, all of the viscoelastic is removed, and the eye is softened to allow the aqueous veins to dilate. Then, after firming up the eye with balanced salt solution through paracentesis, you will see blanching of the vessels in the area of the stent, indicating that it is placed correctly, due to the flow through the stent into Schlemm’s canal (Figures 3 and 4).
If you always do what works best in your hands, then the iStent will be an easy transition, which is of great benefit to your patients.
- For more information:
- P. Dee Stephenson, MD, FACS, ABES, FSEE, can be reached at Stephenson Eye Associates, 200 Palermo Place, Venice, FL 34285; email: eyedrdee@aol.com.
Disclosure: Stephenson reports no relevant financial disclosures.
Streamlined procedure to minimize time and cost, maximize success
Glaucoma is a relentless disease with treatment centered on prevention of optic nerve damage by lowering IOP. One treatment modality is rarely sufficient to stop progression of the disease for the lifetime of the patient, and although drops can be effective in lowering IOP, there are many inherent disadvantages such as expense, inconvenience, side effects and compliance issues. Laser treatment with selective laser trabeculoplasty avoids some of these disadvantages but is not always effective or long lasting.
Image: McCabe CM
Surgically, the mainstay of treatment has been trabeculoplasty and tube shunts, both of which, although effective in lowering IOP significantly, have long-term complications and failure rates that make these tools less than ideal for early to moderate glaucoma treatment. A new class of treatment, MIGS, is exciting in that the complication profile is favorable and the procedures can potentially be performed at the time of cataract surgery with low risk and effective IOP lowering. Currently, the iStent (Glaukos) is the only FDA-approved intraocular MIGS device approved for the treatment of early to moderate primary open-angle glaucoma in the setting of cataract surgery. In the future, there will likely be a variety of devices in the glaucoma toolbox that, in combination, may be even more effective in treating glaucoma, allowing for even greater reduction in IOP.
In learning to implant the iStent, I originally followed the recommendations of the company and implanted the stent after removing the cataract, injecting Miochol-E (acetylcholine chloride intraocular solution, Bausch + Lomb) to constrict the pupil, refilling the anterior chamber with a cohesive viscoelastic (Healon GV, sodium hyaluronate 1.4%, Abbott Medical Optics), tilting the patient’s head 35° away from me, tilting the microscope 35° toward me and looking for the telltale red stripe indicating blood in Schlemm’s canal. This method works well when first learning to implant the iStent. One of the hardest steps initially is visualization of the anatomy with the goniolens in place. This step is made easier with practice. Therefore, I recommend obtaining a goniolens and practicing viewing the angle structures, identifying Schlemm’s canal and placing an instrument, such as a cannula, in the angle to simulate working in this area. This can be done at the end of cataract surgery before starting to implant the iStent. It is important to place a generous amount of viscoelastic on the cornea to avoid air bubbles under the lens with small changes in the position of the gonioprism. Increasing the magnification also helps to identify the correct space and to visualize the depth of implantation.
After becoming comfortable with the recommended implantation technique, I have made some observations that have saved time and viscoelastic, and have increased the ease and success rate of implantation on the first attempt. I now implant the iStent at the beginning of the cataract surgery after entering the anterior chamber, filling with my usual viscoelastic (Viscoat, chondroitin sulphate and sodium hyaluronate, Alcon) and creating the primary incision. Although I normally tape the patient’s head for cataract surgery, I do not tape the head for iStent cases. I then rotate the patient’s head about 45° and ask them to look away from me. I place viscoelastic on the cornea, increase the microscope magnification, and view the angle structures with the gonioprism to ensure that I can visualize Schlemm’s canal readily and that the angle of approach is appropriate. I then orient the inserter to the right side of the main incision and approach the trabecular meshwork with the point of the stent at an angle slightly upward. Upon entering the meshwork, I try to tent the tissue gently away from the posterior wall, flatten the angle of approach so that the body of the stent is parallel to the posterior wall of the canal, and advance the stent along the canal. The button of the inserter is easy to depress in order to disengage the inserter tip from the stent. I then move the inserter away from the stent, observe the location of the snorkel tip and use the closed end of the inserter to gently nudge the device in place if necessary. I like to make sure the exposed end is facing anteriorly away from the iris and flat against the posterior wall of the canal.
The patient’s head is then rotated back to the original position, and the rest of the cataract surgery proceeds normally. I like to see a small “smokestack” of refluxed blood through the iStent snorkel during the lowest pressure portion of the surgery, usually after removing the viscoelastic after lens insertion (Figure 1). By placing the device at the beginning of the surgery, the view is optimal and no additional viscoelastic is needed. Eliminating the rotation of the microscope also makes the procedure more streamlined while still allowing for an excellent view of the angle and easy angle of approach for placing the stent. The iStent insertion device can be used to easily pick up the stent in order to reposition or reload if it is dropped or knocked off during insertion. I find that minimal additional time is needed for this portion of the procedure while providing for effective use of an important tool in the treatment of glaucoma for my patients.
- For more information:
- Cathleen M. McCabe, MD, is the medical director at The Eye Associates, 2111 Bee Ridge Road, Sarasota, FL 34239; email: cmccabe@theeyeassociates.com.
Disclosure: McCabe reports she is a consultant and speaker for Alcon and Bausch + Lomb and receives research support from Glaukos.