A prospective, multicenter, open-label, safety and preliminary efficacy study of the surgical implantation of OPKO's glaucoma drainage device (AquashuntTM) in patients with refractory chronic forms of open angle glaucoma (OAG). The primary objective of this study is to evaluate the surgical implantation, safety and preliminary efficacy of the AquashuntTM after implantation in patients with refractory chronic forms of OAG