Apparatus and methods are provided for treating diseases that produce elevated intraocular pressures, such as glaucoma, wherein the device includes a housing shell defining a cavity between a first end and a second end of the housing shell, and an elastic membrane disposed within the cavity to divide the cavity into a fluidic channel that permits a flow of fluid from the first end to the second end and a sealed cavity. The elastic membrane deforms to change the volume of the sealed cavity responsive to pressure fluctuations between the first and second ends, thereby varying the fluidic resistance of the flow of fluid through the fluidic channel.