A Novel Schlemm's Canal Scaffold: Histologic Observations.

PURPOSE To assess the biocompatibility of a novel implant made of Nitinol (nickel-titanium alloy), designed to improve aqueous humor outflow. MATERIALS AND METHODS In the first arm of biocompatibility testing, microstents were surgically inserted into Schlemm's canal (SC) of 2 non-human primates (NHPs), and a third NHP served as a surgical sham control. After 13 weeks the animals were killed, and the eyes were examined by light and scanning electron microscopy. Two masked investigators evaluated the histology sections. The second arm utilized 8 New Zealand white rabbits; each rabbit received a microstent inserted into the sclera and subconjunctival space by means of passage across the anterior chamber thus providing contact with several representative ocular tissues. The fellow eye of each rabbit underwent a sham procedure without microstent insertion. The rabbits were killed after 26 weeks, and a trained ocular pathologist examined the specimens using light microscopy. RESULTS Histologic and scanning electron microscopy analysis of the NHPs demonstrated that the microstents were located in SC. There was no evidence of an acute or chronic inflammatory response, granulation response, or fibrosis in the outflow system or in adjacent tissues. Rabbit eyes showed minimal mononuclear cell infiltration and minimal fibrotic responses at the site of the implants when compared with sham-treated control eyes. CONCLUSIONS The Hydrus Microstent was associated with minimal inflammation in both NHP and rabbit eyes with extended follow-up. These preclinical studies demonstrate that the Hydrus Microstent appears to have excellent long-term biocompatibility.