A sterile device designed to regulate the flow of fluid between the anterior chamber and the space around the conjunctiva of the eye by allowing flow when the pressure in the chamber is above a pre-set value (e.g., 8 to 10 mmHg). It is typically a very small (e.g., slit) valve implanted in the eye as a component of an eye stent, and typically used in patients with advanced glaucoma when, despite the use of medication, laser treatments, or a previous glaucoma filtration procedure (trabeculectomy), the addition of a drainage tube and valve (aqueous shunt) is recommended.