An eye-implantable device including an eiectrowetting lens is provided that can be operated to control an overall optical power of an eye in which the device is implanted, A lens chamber of the eiectrowetting lens contains first and second fluids that are immiscible with each other and that differ with respect to refractive index. By applying a voltage to electrodes of the lens, the optical power of the lens can be controlled by affecting the geometry of the interface between the fluids. One of the fluids is an aqueous fluid that is isotonic relative to the aqueous humor of the eye to prevent flux of water into or out of the lens chamber. Tims, the lens chamber may be composed of water-permeable materials. Such water-permeable materials may be flexible, to permit the lens to be folded into a smaller profile during implantation.