Eyeworld

GLAUCOMA February 2011 chamber into Schlemm's canal." Dr. Samuelson said one differentiating feature of the iStent is that it does not stent open the canal but rather provides a window through which aqueous flows into the canal. "Its circumferential extension is only 1 mm into the canal," he said. "Keep in mind that the canal itself is about 36 mm long." One natural area of use for the iStent is likely to be in those glau- coma patients who are slated to un- dergo cataract surgery. "One of the things that makes it particularly ap- pealing is that in the FDA trial there was no measurable reduction in the safety of the procedure when com- paring the patients receiving cataract surgery plus iStent versus cataract surgery alone," Dr. Samuel- son said. "So we take one of the most successful and safest proce- dures with the most favorable risk benefit ratio and find that we do not adversely affect it by adding an iS- tent in any measurable way." If adding the iStent to the mix during cataract surgery can make the pa- tient's glaucoma easier to manage, Dr. Samuelson sees it as beneficial to do so. He points out that people have actually been moving away from the combined phacoemulsification tra- beculectomy procedure for the op- posite reason. "Adding a trabeculectomy to a phacoemulsifi- cation procedure adds considerable risk," he said. "While it may lower pressure more, there's definitely a subset of glaucoma patients, i.e., those with early to moderate disease, in which we don't do them a favor by exposing them to that increased risk, unless they really need it." By classifying the glaucoma as early to moderate as opposed to more ad- vanced disease, he thinks that prac- titioners can effectively separate which patients can benefit from a combined iStent or a combined phaco trabeculectomy. Outcomes with the iStent vary depending upon the patient and can be confounded by medication. How- ever, in the recent FDA trial patients were required to be off of their glau- coma medication pre-op. "All of the patients went into the surgery with an average pressure of about 25 mm Hg on no medicines," Dr. Samuelson said. "The average pressure post-op- eratively was around 18 mm Hg at 1 year on 0.4 medicines in the cataract only group and 0.2 medicines in the iStent group—a statistically signifi- cant difference." As a rule, patients were less likely to need to return to medication on the iStent. "There were twice as many patients in the cataract alone group back on medi- cines compared to the group receiv- ing the iStent," Dr. Samuelson said. Assuming the iStent nabs FDA approval, Dr. Samuelson envisions a possible way of expanding the de- vice's usefulness. "There may be other applications for the iStent such as use of multiple stents," he said. "There is work in Canada by Iqbal (Ike) K. Ahmed, M.D., [assis- tant professor, University of Toronto, Toronto] that shows that using more than one stent may ob- tain lower pressures. I don't think that we're going to compromise safety by adding additional stents." Dr. Samuelson thinks that if the use of multiple iStents proves to be safe and minimally invasive while fur- ther lowering pressure, that will ex- pand indications to a higher percentage of patients with glau- coma. Dr. Samuelson sees the EX- PRESS shunt as a more precise, less invasive, safer trabeculectomy. "At least initially I don't see these two stents as competing for the same pa- tient population," he said. "I see the iStent being for early to moderate disease and the Ex-PRESS as a very useful adjunct to trabeculectomy for patients with more advanced dis- ease." On the EX-PRESS track Robert D. Fechtner, M.D., professor of ophthalmology, Institute of Oph- thalmology and Visual Science, New Jersey Medical School, University of Medicine & Dentistry of New Jersey, Newark, N.J., described the EX- PRESS as a small, stainless steel de- vice that has a narrow aperture to provide some resistance to flow through the device. "It replaces one step of the trabeculectomy proce- dure," he said. With a full-fledged trabeculec- tomy, after the flap is created the surgeon enters the eye and removes partial thickness cornea 0.5 mm to 1 mm or more. "This essentially cre- ates a zero resistance channel to out- flow and allows the eye pressure to drop to near atmospheric pressure," Dr. Fechtner said. "We then restore resistance by suturing the flap in place." Use of the EX-PRESS standard- izes one part of the procedure. "Once the flap is created, we enter under the flap with a small needle, typically 25-27-gauge, and insert the Funneling continued from P. 73 58-81 Feature_EW February 2011-DL2_Layout 1 2/4/11 2:31 PM Page 74

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