OCT 08, 2020
This prospective study used in vivo anterior segment OCT (AS-OCT) imaging to assess the relationship between iStent positioning, iridocorneal angle structures and surgical outcomes.
Investigators enrolled 54 eyes (42 patients) with cataract and mild to moderate open-angle glaucoma that underwent cataract extraction and received 2 iStent inject devices. The control groups included 30 unoperated fellow eyes and 25 unrelated eyes that underwent standalone phacoemulsification. Patients were followed for 12 months. Imaging was performed after 3 and 12 months to evaluate stent position and Schlemm canal diameter. Surgical outcomes were defined as successful when unmedicated IOP was 18 mm Hg or less.
At 12 months, mean medicated IOP decreased by 8.7% (P=0.04). The use of topical antiglaucoma medication declined in 82% of eyes, with the number of medications dropping from 1.8 to 0.5 (P<0.001). By the end of the study, both microstents were visible by gonioscopy in 65% of eyes while only 1 stent was visible in the remaining eyes.
The number of visible devices on gonioscopy was a strong predictor of success (RR 0.41). Imaging revealed that 55% of cases had a visible portion of microstent protruding an average of 64 μm (range 0–173 μm) into the anterior chamber. The success rate among eyes with at least 1 protruding iStent was 65% compared with 40% in eyes with both devices buried within the trabeculum. There was no difference in the positions of the devices between 3 and 12 months postoperatively, indicating that the position was likely stable from time of implantation.
This was a single center study with only 2 surgeons and a rather homogenous patient population, which may limit wide application of study results. Researchers did not perform a medication washout—which limits this study's ability to determine the IOP-lowering effects of the iStent inject—but this is a more likely representation of real-world use of the device.
In this study, there was a high rate of positioning the iStent devices too deep within the trabeculum, which strongly associated with failure to achieve surgical success. Stability of the device’s position over time indicated that this deep placement likely occurs at the time of surgery. Surgeons performing MIGS should take care to implant these microstents at the proper depth. Upcoming changes to the design of the iStent might make correct placement easier to achieve and may improve efficacy of the device.