A contact lens for treating binocular diplopia, the contact lens comprising: a central region adapted to degrade light passing therethrough, so as to create a central scotoma in a patient's eye in which the contact lens is placed in use; and a peripheral region adapted to degrade light passing therethrough to a lesser extent than in the central region, or not at all; such that, in use, an image in the field of view of the said eye is degraded only in the center or to a greater extent in the center than in the periphery. Also provided is a method of manufacturing such a lens, and a method of treating binocular diplopia comprising applying such a lens to a patient's eye.