Cataract surgeons should be familiar with and consider performing micro-invasive glaucoma surgery (MIGS). Use of this technology allows the combination of relatively low-risk MIGS implantation with cataract surgery. I’ve provided here some surgical pearls to help improve success with the iStent from Glaukos, the only FDA-approved MIGS product.
We are constantly looking for additional treatment options that can better manage the glaucoma disease process with fewer risks and side effects than current modalities.1 One great approach is to combine treatment with a common procedure, such as cataract surgery, which MIGS allows.
Clinical evaluation
It is estimated that 20 to 25 percent of patients with visually significant cataracts also have a history of elevated intraocular pressure (IOP) and have been or are being treated with glaucoma therapy. Cataract surgeons should keep this in mind, as it may provide the only opportunity to use this technology since the iStent is approved for use in conjunction with cataract surgery.
Any patients on glaucoma drops, whether their glaucoma is controlled or uncontrolled, should be evaluated to see if they are appropriate candidates for MIGS implantation. For those who are controlled, successful implantation of the iStent can help reduce the number of drops needed.2,3 Those patients whose glaucoma is uncontrolled with drops stand to benefit from IOP reduction from both cataract extraction and placement of the stent.
The management of uncontrolled patients is becoming especially important as cataract surgery is becoming the more preferred first-line surgery for glaucoma patients. Removing a cataract prior to more traditional glaucoma surgeries can achieve a mild to moderate IOP reduction. It also helps prime those eyes to be more successful should they need a trabeculectomy or tube shunt. This is done by deepening the anterior chamber, which makes surgery easier to perform and removes an inevitable visually significant cataract and its inflammatory side effects.
Gonioscopic examination at the slit lamp should be performed to assess if there is appropriate space and to assess landmark appearance. Remember that the goal is to place the iStent in the superior third of the pigmented section of the trabecular meshwork. If this landmark is not seen either due to shallowness of the angle or other existing pathology, such as peripheral anterior synechiae or neovascularization, then the iStent should not be placed.
Surgical Pearls
The following are tips that I consider useful during combination iStent-cataract surgery, that go beyond those routinely given, for anyone beginning to use the iStent or having difficulty placing it.
Right or left?
The iStent is a nonferromagnetic titanium micro-bypass stent that comes in both right (GTS100R) and left (GTS100L) versions, which means that there is one for forward or backward placement regardless of which hand the surgeon uses.4 It was designed so that it could be placed in either eye toward the inferonasal quadrant, in which there are more collector channels, as witnessed by increased trabecular pigmentation. However, the iStent can be placed pointing toward the superonasal quadrant and still be effective. Surgeons more comfortable with only forward or backward placement can consider placing the iStent the same way no matter which eye is undergoing surgery.
Turn the head ... more, more
Proper visualization of the anterior part of the eye is the single most important factor for easy, safe and successful iStent placement. Before surgery, I routinely tell patients that I will ask them to turn their head significantly at some point so that they know to expect it. They embrace and grant this request as they know their cooperation will help make the surgery more successful. It also removes any questions they may have as to why it was done and brings up any issues the surgeon should know about preoperatively if the patient is unable to do so because of another medical condition. Once a patient’s head is turned during surgery, encourage the patient to turn even more as every little bit helps. Also make sure to angle the microscope as much as possible to help create the best angle for visualization. (See Video 1).
Practice gonioscopy
The use of a gonioscopic lens during surgery does take practice, especially for those who don’t traditionally perform angle surgery. One suggestion is to examine the angle with a gonioprism in patients who have completed cataract surgery only. This helps in learning how much (or how little) pressure to put on the lens. Remember to lighten up if you see corneal striae. There are also options regarding which lens to use, including the fixed Swan-Jacobs lens or a newer lens called the Vold gonioprism that pivots. Test them out to see which is more comfortable.
Less OVD for less IOP
It is natural to want to fill the anterior chamber with more OVD to help deepen the angle to see the landmarks better and elevate the IOP so the gonioprism sits more easily. In this case, the addition of more OVD removes a very good target for the iStent.
Just after cataract extraction and placement of the IOL, the eye is slightly hypotonous, which helps bring out the blood in Schlemm’s Canal, which is the site of your target. This is especially useful in patients with little trabecular pigmentation in whom using other landmarks becomes critical. (See Video 2, in which there is pigmentation, versus Video 3, in which there is less pigmentation).
Remember that the goal is to thread the tip of the stent past the trabecular meshwork and into Schlemm’s Canal just like placing an IV line. If the canal is collapsed because the eye is overinflated then threading into that space becomes difficult. The presence of blood in the canal also is useful to help confirm successful placement of the iStent as there will be a plume of blood (although seeing blood may be uncomfortable the first few times it is done).
Regrasping iStent
Inevitably, situations will occur in which the stent is not in proper position in the anterior chamber after release from the inserter. At these times, there are a few options for the surgeon. One choice is to regrasp while still in the eye. (See Video 4). For this method, use the trabecular meshwork to give support from behind as the iStent is being grasped. Remember not to fully press down on the shooter as there is a tendency to overshoot the stent while regrasping, leaving the surgeon with a malpositioned stent on the shooter. Another option is to bring the stent out of the eye and reposition it using a tray. (See Video 5).
Conclusion
MIGS technology, including the iStent, provides additional and safe options for patients with glaucoma. Given the common need to address cataracts in patients, any option that more easily treats glaucoma with fewer drops or provides a chance to control it should be considered.
References
1. Francis BA, Singh K, Lin SC, et al. Novel glaucoma procedures: a report by the American Academy of Ophthalmology. Ophthalmology. 2011;118(7):1466-1480.
2. Samuelson TW, Katz LJ, Wells JM, Duh YJ, Giamporcaro JE; US iStent Study Group. Randomized evaluations of the trabecular micro-bypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology. 2011;118:459-467.
3. Craven ER, Katz LJ, Wells JM, Giamporcaro JE; iStent Study Group. Cataract surgery with trabecular micro-bypass stent implantation in patients with mild-to-moderate open angle glaucoma and cataract: Two-year follow up. J Cataract Refract Surg. 2012;38:1339-1345.
4. Ichhpujani P, Katz LH, Gille R, et al. Imaging modalities for localization of an iStent. Ophthalmic Surg Lasers Imaging. 2010;41(6):660-663.