Abstract: A system for producing a three-dimensional image of a surface, such as a surface of a cornea, includes a laser beam that passes through a beamsplitter and an objective lens to produce a spherical wavefront that impinges on the cornea and is reflected by the cornea as a return beam back through the objective lens. The return beam is reflected by the beamsplitter through an imaging lens that focuses the return beam onto an imaging screen, through a dual phase plate, and onto a photosensitive array. The dual phase plate includes two sets of spaced periodic refractive features spaced along orthogonal directions. The phase plate is modulated by incrementing it at a 45 degree angle relative to the first and second directions, thereby simultaneously producing phase shear along the two orthogonal directions.