As a third-generation comprehensive ophthalmologist in a rural community in Minnesota, minimally invasive glaucoma surgery (MIGS) is a big part of my practice. I see a large volume of cataract patients in my practice, and because about 1 in 5 cataract patients also have glaucoma,1 I am often faced with the challenge of managing intraocular pressure (IOP) in these patients as well. I strongly believe as a comprehensive ophthalmologist, it’s my duty to look more holistically and ask what we can do for the whole eye that can be effective, lower risk and have a favorable safety profile, in order to intervene earlier to treat any potential glaucoma threat.
Glaucoma affects about 70 million people worldwide and about 4 million in the United States—80% of which have primary open-angle glaucoma (POAG), which equates to about 3 million people as a conservative estimate.2,3
New attitudes about the trabecular meshwork
Admittedly, the trabecular meshwork (TM) was largely forgotten for many years. The revival of this space has made it possible to reduce IOP and potentially reduce or eliminate a patient’s need for a drop in the long-term, which might improve both adherence (whether it be for other glaucoma medications or follow-up visits) and the burden to the ocular surface. By creating and maintaining a channel between the aqueous humor in the anterior chamber and Schlemm’s canal, iStent infinite® can bypass the site of highest resistance to aqueous outflow: the juxtacanalicular trabecular meshwork.4
I completed my residency in 2011 when there were fewer minimally invasive glaucoma surgeries (MIGS) available, but I credit the first-generation iStent device (iStent G1) with creating a passion in the glaucoma space. Now we have more of an opportunity and the advancements necessary to surgically intervene a bit earlier; especially for cataract patients who are at higher risk for elevated intraocular pressure (IOP), advancing optic nerve changes, and characteristic visual field loss. While there are many appropriate MIGS procedures currently on the market, I tend to select the iStent infinite, which has three anatomically designed stents preloaded into an injector system.
What you should know about advancements in angle-based surgery
Because I used iStent G1, I was able to gain experience with angle-based surgery. Since then, the technology has leaped forward to where the stents are now placed in the angle instead of sweeping along it.
My transition to using the iStent infinite has been a straightforward one. I don’t mean that in a way that I take surgery lightly, but once you are comfortable working in the angle, the design of the iStent infinite makes it easy to maneuver in the TM. I especially like the new changes from the iStent inject W® to the iStent infinite. For example, the sleeve (insertion tube) is the gateway that prevents viscoelastic from leaving the eye. Additionally, when you use the stent delivery button, you don’t lose visualization with the viewing slots and window in the insertion tube. I appreciate that I can use the stent activation button as many times as I like and that this device can be used for a full 240 degrees in the angle.
I’m forever grateful for learning the ins and outs of angle-based surgery during my residency with iStent G1. Subsequently, this experience improved my confidence as I transitioned to iStent Inject W, which contains 2 preloaded stents. Since then, Glaukos has redesigned the device where the iStent infinite features three stents and can be used directly in the angle. The benefits for me as a surgeon are that I’m only using 3% of the angle—which means 97% of the trabecular meshwork is untouched.5
Questions I ask before adopting new surgical techniques
Before I begin with any new surgical device or therapeutic drug, I always ask myself whether there is peer-reviewed literature supporting the treatment’s safety and efficacy. Next I question if it makes sense for the patient in terms of their individual glaucoma care. iStent infinite has become another tool in my surgical armamentarium, especially if I have a patient who isn’t responding to or is intolerant to medical therapy and has failed a prior glaucoma surgical treatment. If so, the next step in my decision-making leads me to ask the question as to what might be an optimal treatment option for the patient? Should I try another filtering surgery? Do we have advanced glaucoma requiring a tube? If they’ve had a tube, do we elect to proceed with a gel stent? Or, do we simply monitor and co-manage the patient’s case with the eyecare provider (ECP)? I think about all of it.
My experience with iStent infinite
I started with the iStent infinite in standalone procedures, meaning my treatment goal is to manage IOP while leaving the patient phakic until they might need cataract surgery. Transparently, it can be a challenge to adopt a new device on the market due to financial pressures as well as training staff. But for our practice, this MIGS procedure made sense for the majority of my patients, especially for those who had previous surgeries or failed trabs or tubes. To be clear, I do consider different angle-based procedures as failed therapy, including Xen® Gel Stents, trabeculectomy, or tubes. These devices are appropriate treatment options depending on the level of glaucoma severity, but maybe they aren’t getting pressure to where we need it to be.
Initially, I was doing iStent infinite as a standalone procedure on patients whose IOP fell into the mid-20’s and were taking approximately three different medications. As a practice, we decided that before going to another subincision or filtering surgery, we would consider iStent infinite.
After performing multiple standalone iStent infinite procedures, we were collectively amazed by our initial surgical outcomes for these glaucoma patients. Further, we have data from the pivotal trials that demonstrate that even with maximal medical therapy, these patients still had IOPs in the mid-20's.2,6 Those results have been mirrored by what I’ve been seeing in real-world cases. For an angle that’s been untouched, those patients who may not have responded to previous treatment respond well to the iStent Infinite, where I’m now able to potentially reduce most patients’ IOP to the mid-teen range.
Right now, I’ve implanted the iStent infinite in about 20 patients. We start with one eye, and typically the patient response leads me to proceed with the other eye. To be able to go back to the angle and only touch 3% of the trabecular meshwork2 has been demonstrated in the data to be beneficial to these patients. In totality, my confidence in this standalone procedure continues to increase based on my surgical experience and how it has impacted the care of my chronic POAG patients.
How do we approach refractory glaucoma today?
The definition of refractory glaucoma has changed. It’s no longer just for patients with severe POAG anymore or with just a central 5 degrees of vision. This is more about how tolerant they are of medical therapy. Maybe they can no longer take medication because of the side-effect profile or they are unable to take certain medications due to compliance issues. Then we shift our focus externally to ocular surface disease with conditions such as dry eye, which can further complicate their issues and influence how we treat our patients. Now, I consider refractory glaucoma to encompass the spectrum of glaucoma patients from mild to moderate to severe.
How quickly can you see IOP results?
I have seen immediate results, with the caveat of delayed response if residual ophthalmic viscoelastic device (OVD) happens to have been left behind in the eye or the case exhibited reflux hemorrhaging, which caused IOP elevation. Typically I will see pressure decrease to the mid-teen range unless they have a steroid response at the one-week, post-op visit—because I do put these patients on steroids for a short time. I have 6-month and 9-month data from my practice that is very solid. In professional medical opinion, I can appreciate seeing the 24/7 IOP control versus the fluctuation we tend to worry about when we rely on patient adherence to their medical therapy.
Dr. Ristvedt’s practical and ergonomic pearls for using the iStent infinite
- When you’re working in the angle, it’s imperative to have an en face view, meaning you are looking right at the TM—which is key no matter what device you are using. Before anything, be used to seeing that en face view.
- Decide if you are more comfortable with the gonioscopy prism in your non-dominant hand, or if you want more of a free-floating prism. Personally, I like to make my incision so that my dominant hand isn’t rotating back towards my pinky, because it can be difficult to get that movement. I find that forward movement of sweeping towards my thumb is easier and important for getting the full 240 degrees, especially if I’m not performing this surgery in conjunction with cataract surgery.
- Once the incision is made, I like to fill the eye with OVD. Usually I fill it with a cohesive OVD rather than a dispersive when I’m doing it as a standalone procedure, because it comes out of the eye much easier when you’re not using intracameral anesthesia. When I’m performing a stand-alone procedure and ready to go, I like to start towards my pinky, as far as I can go. I rotate my body and scope towards that.
- After I place the first stent, I move towards the middle and sometimes shift my microscope towards my thumb while staying in the eye. Remember that the sleeve of the iStent infinite prevents the OVD from coming out of the eye to maintain the stability of the anterior chamber.
- The final step is to place the last stent.
- I think the main thing is to make sure you are comfortable with floating this device in a wide span. I don’t like to come out of the eye, because that can potentially lead to more OVD leakage from the eye. In terms of stability of the anterior chamber, being able to use your body and have the second hand for the microscope is essential.
- If you are a brand-new surgeon, you may want to do the “easy angle” first, so you can gain confidence in your early cases and have a smoother learning curve. From there, you can go to the middle and then the third.
Tips for how to talk to patients
There is a paradigm shift from telling a patient to take drops compared to a procedure. For a procedure, my conversation is more organic.
I always ask if they remember their experience with cataract surgery. I ask what it felt like and most respond that they didn’t experience any pain. I ask about the recovery, and they usually respond that it was straightforward. Maybe vision was blurry for a few days but then it cleared. I start with that conversation so they can identify with their own personal experience that will take place in the operating room when we do the iStent infinite.
— Dr. Deborah Gess Ristvedt, DO
When patients hear that what I’m doing will allow fluid to leave the eye in the natural outflow pathway without doing anything potentially more invasive, they tend to be relieved.
If we ask patients how they are doing with their drops, it's tough to know if their responses are truly honest. In some cases, it’s a bit like flossing before you go to the dentist the next day. Are they really taking those drops every day, and are they really getting them into their eye? Are they afraid of disappointing me? iStent infinite can be an appropriate surgical option to take the guesswork out of the treatment equation.
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