At the AGS Annual Meeting, Cody Manzanero, MD, presented results of a study that found that combined phacoemulsification and iStent implementation was efficacious and safe in patients with low-tension glaucoma.
Cody Manzanero, MD:
My name is Cody Manzanero. I am one of the residents at the Medical University of South Carolina (MUSC). I am presenting at AGS this year a project that was titled “36-Month Outcomes of Combined iStent Implementation and Phacoemulsification in Patients with Low-Tension Glaucoma.” At MUSC, we pursued this study with a team here of our glaucoma experts. We looked at this study in particular because there is a lot of information on the use of the iStent device in primary open-angle glaucoma patients, and there’s good long-term data in those patients. However, there’s a distinct lack of long-term data specifically in the low-tension glaucoma patients. Although short-term data around a year in previous studies is encouraging, the critical question remains if this is a sustainable method long-term or if the device is efficacious long-term in these patients. That was our specific goal in this study was to look at the long-term efficacy and safety of the iStent device in patients with low-tension glaucoma.
Our study was a retrospective cohort of 36 low-tension glaucoma eyes in 36 patients that underwent combined phacoemulsification and iStent implementation. Our minimum follow-up time was 24 months; 22 of our patients completed the total 3-year follow-up. Our primary outcomes were measured using 36-month cumulative success probabilities with a Kaplan-Meier survival analysis. We defined success in 2 different ways. There was complete success, which was meeting certain intraocular pressure thresholds without medications. These thresholds were 18 or below, 15 or below, and 12 and below. Additionally, we had a group of qualified success, which was meeting those same intraocular pressure thresholds while on the same baseline level of medications or below prior to surgery. Our secondary outcomes included stability in Humphrey Visual Field, which was measured using mean deviation at baseline in their last follow-up, and then rates of postoperative interventions and complications over a 36-month period.
The findings of our study included at two years, there was a significant drop in intraocular pressure, roughly about 3 points, and there was a half a medication decrease on average, meaning that every other patient decreased by one medication. At year 3, those findings were sustained with a similar 3-point pressure drop found from baseline to the patients that were followed 3 years. As far as our Kaplan-Meier success probabilities for complete success, meaning that you met certain intraocular pressure thresholds without any medication, which the thresholds were 18 and below, 15 or below, and 12 and below. For those that were in the 18 or below category, there was a 14% success rate, and in the 15 and below thresholds, there was a 6% success rate, and that’s without any medications. Those who were on their baseline or lower amount of medication, but still on medications, which would be qualified success. At 3 years, 21% of them were at IOP of 12 and below, 57% of them were at an IOP of 15 and below, and 77% of them were at an IOP of 18 or below.
Then as far as our secondary outcomes, there was Humphrey Visual Field stability throughout the 3 years as defined by mean deviation at baseline and comparing the mean deviation to baseline and at the end of 3 years or the last follow-up date. Only 2 postoperative complications were noted in our study population, one being a transient intraocular pressure spike, which only lasted within the first postop week, and then a prolonged period of acute iritis that required after surgery. It was within first 2 months of after surgery that required more than a month of a steroid taper and resolved after the prolonged steroid taper. Only 1 patient required an additional procedure, which was SLT more than a year after receiving the iStent implant, and there were no patients that required additional incisional surgery in the 36-month period.
As far as what we concluded from this study, we found that iStent is, at the time of phacoemulsification, is a safe way to get a modest IOP reduction in patients with low-tension glaucoma, and definitely a safe and effective way to meet mid-teen pressure goals in low-tension glaucoma patients. How this may impact the field of glaucoma? It only provides further evidence to support the use of this device at the time of phacoemulsification in patients who want an efficacious and safe procedure to be done at the time of cataract surgery, and those who have mid-teens pressure goals.
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