MIGS Takes a Step Forward

The iStent puts microinvasive glaucoma surgery in reach.

By John Berdahl, MD

The Glaukos iStent is the first major player in a new frontier in glaucoma surgery known as MIGS, or micro-invasive glaucoma surgery. MIGS procedures are a breakthrough because they allow the surgeon to reduce IOP by improving aqueous outflow through the natural physiologic pathway. At the same time they preserve ocular tissue and future treatment options that could help maintain long-term vision.

MIGS is significantly less invasive to the patient than other types of implants. Recovery times are shorter, it’s highly effective at lowering IOP, and patient recovery is similar to cataract surgery alone. An additional advantage is that MIGS offers patients far better vision postoperatively than traditional glaucoma surgeries do.

Thus far, iStent (Glaukos Corp., Laguna Hills, Calif.) is the only device FDA-approved and commercially available to make MIGS possible. I’ve been using it since its FDA approval last June, so let me explain how to reap the benefits of this first in a new class of glaucoma devices.

Patient Matchmaking

The iStent is indicated for use in combination with cataract surgery to reduce IOP in adults with mild or moderate openangle glaucoma and a cataract who are currently using IOP-lowering eyedrops. It is implanted during cataract surgery. I will use it for in primary open-angle glaucoma, pseudoexfoliation glaucoma, pigment-dispersion glaucoma and uveitic glaucoma for any patient who has a functioning trabecular meshwork that I can visualize. Closed angles are a contraindication for this stent, but still quite a high percentage of glaucoma patients can benefit.

The iStent (circle) is 1 mm in length and 0.33 mm in height.

One type of patient for whom the iStent is appropriate is the one with progressive glaucoma despite maximal medical therapy and who has had previous cataract surgery, but whose overall health makes the patient unsuitable for a trabeculectomy or tube shunt. A classic example is an 83-year-old woman with high IOP and on maximal medical therapy. I know I need to buy some time for this patient, but I also know she may not tolerate extensive glaucoma surgery.

Additionally, I will often use the iStent as an off-label use in pseudophakic patients.

Time Not an Issue

Implantation of the iStent is elegant. When combining the implantation with cataract surgery, place the stent through the clear cornea incision and visualize the trabecular meshwork under a gonio prism. Then place the stent. It adds only five to 10 minutes to the cataract procedure. As a single procedure, it would probably take 10 minutes to implant this stent. When you consider that 30 minutes to an hour is required for a traditional glaucoma surgery, the iStent’s brief placement time is appealing indeed.

IOP Reduction

While the iStent will provide a reduction in the patient’s IOP, surgeons need to understand that the iStent is not going to lower IOP as effectively as a trabeculectomy or a tube shunt. However, it will lower IOP more safely than traditional glaucoma surgeries. Further, it preserves all our options down the road if the patient does not reach the target IOP. Research by Ike Ahmed, MD, demonstrated two stents can consistently reduce IOP to less than 15mm Hg, and we can do any of our traditional glaucoma surgeries on top of the iStent.¹

Another point about IOP reduction with the iStent is that is it is still bound by episcleral venous pressure. That is, you will not encounter the hypotony that occurs with traditional glaucoma surgeries. Episcleral venous pressure, in the 9 to 10 mm Hg range, still limits how low you can get the pressure.

One other point to keep in mind: Though I have not encountered any complications from the iStent, you may occasionally see a hyphema in the first few days postoperatively. This typically resolves on its own.

Lighten Patients’ Medicinal Load

Given the widespread problem of patient compliance with glaucoma medications, another, and significant, advantage of the iStent is that it allows the patient to reduce his or her regimen. If the patient is on more than one medication, I usually discontinue either the alpha-agonist, carbonic anhydrase inhibitor or beta-blocker. I keep the patient on a prostaglandin.

Implanting the Glaukos iStent in a MIGS procedure. It typcially adds only five to 10 minutes to a cataract surgery.

Should a prostaglandin be the patient’s sole glaucoma medication? I have found I can almost always stop that, too, leaving him or her medication-free. Patients are happy to lower their medication burden.

Refractive Neutrality Option

Another benefit of the iStent patients may appreciate is that it’s neutral in terms of refractive error. This, of course, sets it apart from traditional glaucoma surgeries that often induce astigmatism. Now I’m confident enough to do this in patients with mild glaucoma in combination with cataract surgery and a premium IOL, such as a toric lens or a Crystalens (Bausch + Lomb, Rochester, N.Y.), in an effort to limit their need for glasses after cataract surgery.

With traditional glaucoma surgery, that was not an option. We were not good stewards of the patient’s dollars and eyes by combining a traditional glaucoma surgery with a spectacle-independent option for cataract surgery. We just could not achieve it. Now we can.

The iStent is a valuable tool in our fight against glaucoma. Keep in mind, however, that the keys to performing this surgery are a good understanding and visualization of the trabecular meshwork anatomy. Without them, you will not be able to put the stent in the right place. OM

Reference

1. Belovay GW, Naqi A, Chan BJ, Rateb M, Ahmed II. Using multiple trabecular micro-bypass stents in cataract patients to treat open-angle glaucoma. J Cataract Refract Surg. 2012;38:1911-1917.

John Berdahl, MD, is in private practice in Sioux Falls, SD. He is a consultant with Alcon and Bausch + Lomb. Contact him via e-mail at johnberdahl@gmail.com.