Despite many therapeutic options, some glaucomas remain refractory to treatment and intraocular pressure remains elevated or there is a progression in visual field. When conventional therapies and operations fail or the theoretical chances of success are low (for example, neovascular glaucoma), implantation of an artificial drainage device system is used as a last resort. Artificial drainage systems create a link between inside and outside the eye and lower intraocular pressure. Characteristics of Ahmed valve, Surgical technique.