KEY TAKEAWAY POINTS
• The mechanisms of action of the HYDRUS Microstent include trabecular meshwork (TM) bypass, Schlemm’s canal scaffolding, and 90 degree span, or about 3 clock-hours of canalicular drainage; the mechanism of action of iStent Inject is to create a bypass through the TM into Schlemm’s canal
• Data from preclinical models can help surmise the theoretical potential of MIGS implant devices
• Information found in the product labeling describing proper insertion of a MIGS implant is important to ensure its function to increase aqueous outflow to reduce IOP
• Per the product labeling, proper placement of the HYDRUS Microstent can be verified by visualizing the three windows behind the TM using intraoperative gonioscopy; intraoperative gonioscopic verification of proper iStent Inject W placement per the Instructions for Use may not adequately confirm proper placement of the head of an iStent Inject W into Schlemm’s canal
• A study evaluating postoperative NIDEK Gonioscopy to verify placement demonstrated a large proportion of misplaced iStent Inject implants with IOP reduction from an unknown component attributable to either cataract surgery or iStent Inject at 1 year
• A study evaluating the use of anterior segment optical coherence tomography (AS-OCT) to verify proper placement has also shown that a substantial proportion of the flanges and heads of implanted iStent inject devices are misplaced, potentially compromising their ability to reduce IOP, again showing an IOP reduction from an unknown component attributable to either cataract surgery or iStent Inject at 3 months
• There are no publicly available data demonstrating a scaffolding effect beyond the immediate region of a properly placed iStent Inject W that is solely attributable to the implant
• Although AS-OCT demonstrated an increase of Schlemm’s canal dimensions after iStent Inject placement, standalone phacoemulsification has also demonstrated substantial Schlemm’s canal dilation using swept source optical coherence tomography (SS-OCT)
• Although intraoperative optical coherence tomography (iOCT) can assist to verify, or allow repositioning of a HYDRUS Microstent in difficult cases, the head/thorax of an iStent Inject W cannot be visualized using iOCT due to signal loss, making verification of proper iStent Inject positioning questionable