Biocompatibility of the Ex-PRESS miniature glaucoma drainage implant

Purpose: Based on lessons learned from earlier attempts, a novel miniature glaucoma implant, Ex-PRESS, was developed in 1998. The current study summarizes the histopathologic evaluation of this device implanted in the eyes of rabbits. Methods: The device was implanted into the anterior chamber at the corneoscleral junction in 1 eye each of 8 white New Zealand rabbits, while the contralateral eye served as control. Three and 6 months after implantation, the rabbits were killed and their eyes were enucleated and processed histologically, leaving the device in situ when sectioning. Results: Three and 6 months postoperatively, the local tissue reaction typically consisted of an enveloping, thin, mature, fibrotic capsule (thickness <0.04 mm), devoid of inflammatory cells. This capsule surrounded approximately 25% of the implant surface area present in the sections. The lumina of the devices were devoid of inflammatory exudates or other obstructions in all specimens examined, suggesting free flow of fluid. Conclusions: The implantation of the Ex-PRESS miniature glaucoma shunt resulted in minimal capsular reaction. Considering the high reactivity of the rabbit eye, it is possible that this implant will induce a smaller cellular inflammatory reaction in the human eye.