Eyeworld

EW GLAUCOMA 45 by Ellen Stodola EyeWorld Staff Writer Expanded uses of the iStent Physician is targeting placement of the device and using multiple stents per case W ith the advancement of microinvasive glau- coma surgery (MIGS) devices for the treat- ment of glaucoma, uses of technology like the iStent (Glaukos, Laguna Hills, Calif.) are expanding. Iqbal "Ike" K. Ahmed, MD, assistant professor of ophthal- mology, University of Toronto, and head of ophthalmology, Trillium Health Partners, Mississauga, Ontario, is one surgeon who is looking at the expanded uses. These include targeted placement and using multiple stents in one eye. Dr. Ahmed—who recently gave the Binkhorst Lecture at the 2014 ASCRS•ASOA Symposium & Con- gress on the topic of MIGS, a term he coined—said that he has been working with the iStent for about 5 years now, initially using it as a sin- gle device in a combined phaco case. "Over the years [I] have tweaked the procedure to use multiple iStents, taking advantage of a larger access of aqueous drainage outflow, as well as targeting them, placing them strategically in the eye at certain locations," he said. What can targeted placement accomplish? The targeted placement is in terms of aqueous outflow. The aque- ous conventionally drains through the trabecular meshwork, and as glaucoma is a trabecular meshwork disease and because of increased resistance and insufficient flow, the flow gets into the canal from there, he said. "What we're doing is trying to tap into the larger aqueous veins that emerge from the canal." Dr. Ahmed compared the canal to a highway off of which there are numerous other roadways. He is trying to find the location of those roads that lead off the canal, espe- cially the large roads with multiple lanes, and place the implants right in those locations, he said. The roads that he is referring to are the aqueous veins, and there are only a few of these in each eye. If a surgeon can successfully find an aqueous vein and put the device right at its opening, Dr. Ahmed said that "will allow aqueous to go directly into the aqueous vein with the least resistance and that will have the highest chance to lower pressure." This is important because even one aqueous vein can handle about half of the eye's production of aqueous. Multiple targeted placements can lead to improved efficacy and a lower pressure target. "We've learned that by placing more than one, not only does it provide a greater access of flow over multiple aqueous veins, it also improves the chance of getting close to a major one," he said. It is important to get the stents in properly. Although it is not diffi- cult to place them superficially, it may require some effort to make sure the implant goes in correctly and is positioned properly within the canal and not superficially within the trabecular meshwork tissue. "That requires a real under- standing of surgical technique and careful observation to ensure it's placed right," he said. Results Dr. Ahmed said that the use of multiple iStents, targeted multiple iStents, and targeted single iStents have shown improved results. "That being said, a single implant is still efficacious and can get pressures into the mid to high teens," Dr. Ahmed said. "For many patients, that's reasonable." However, he said that for patients who he wants to get even February 2011 June 2014 E ver since the iStent was approved in 2012, surgeons have focused on optimizing placement and improving efficacy. This is natural and expected in a glaucoma implant because reducing pressure safely is the goal of our therapy. Ike Ahmed, MD, has been a leader in targeted iStent placement and generally advancing our knowledge of the iStent. In this month's "Glaucoma editor's corner of the world," Dr. Ahmed shares his insights. One of the greatest challenges in developing a glaucoma implant for the aqueous outflow system is that we don't have a clear understanding of how it works. A cardiologist looking at glaucoma would expect that we would have an outflow angiogram to help guide our interventions. But the flow is too slow and too complex for anything similar to a coronary angiogram. Therefore, our interventions are based on circumstantial evidence and other indirect information. It will be interesting to see whether the increasing use of the iStent will encourage work on the outflow system to give us more direct ways to target the high flow areas and also be able to assess the impact of the iStent and other MIGS devices. Investing in the development of outflow imaging technology makes more sense now that we have MIGS and can intervene in this pathway. Although the outflow system is interconnected, it seems to be segmental, and a device placed at one point does not access the entire system. Furthermore, outflow may be greater in one area than another. These observations have led to the suggestion that we use multiple iStents and try to place them in areas of higher outflow. Dr. Ahmed has done critical work in these areas, and we are fortunate to have his innovative observations. Reay Brown, MD, glaucoma editor continued on page 47 Three episcleral veins are highlighted by yellow arrows, with the blue arrows indicating the likely origin of the veins as aqueous veins feed into these at the limbal area. By noting the location of these veins and using targeted placement of the iStent, surgeons may be able to improve results. Source (all): Ike Ahmed, MD Glaucoma editor's corner of the world Watch this video on your smartphone or tablet using your QR code reader. (Scanner available for free at your app store.) The arrows point out a nice flow of aqueous influenced by a microstent placed in the vicinity of the opening of that aqueous vein. 45-47 Glaucoma_EW June 2014-DL_Layout 1 6/3/14 12:35 PM Page 45

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