The AGV implant is designed to open when the IOP is between 8 mmHg and 10 mmHg, and thus maintains an IOP of 8 mmHg or higher. In the early period after glaucoma drainage device (GDD) surgery the intraocular pressure (IOP) classically goes through 2 phases. The hypotensive phase occurs immediately after surgery, lasts around 1 week. This is followed by the hypertensive period where the IOP tends to rise steadily above 21mmhg.