Abstract: An ocular prothesis is provided in which a prosthesis housing has a bore therein for receiving elements to simulate the iris and pupil of an eye. A black disc is received within the bore and covered by an active disc having a central aperture therethrough exposing a portion of the black disc to represent maximum pupil constriction. The active disc has one or more rings concentric with the aperture, such rings being made from a photochromic material such that at various light intensities the rings change from translucent to opaque. Accordingly, at low light levels with the rings transparent, a greater portion of the black disc is apparent, giving the appearance of a dilated pupil. As light levels increase, the rings sequentially become opaque from the largest ring to the smallest, giving the appearance of pupil constriction.