Abstract: A surgical apparatus for partially modifying the curvature of the cornea of an eye while the eye is within the patient is disclosed. The device is able to ablate a zone of corneal material in the form of a lenticular lamina. The thickness of the lamina at any particular point on the cornea surface varies as a function of the radial distance between that point and the central optical axis of the eye. The surgical apparatus comprises: a source of light (31) capable of emitting a beam of light (4) having a wavelength which is about 200 nanometers; an optical system (32) for directing and focusing the beam of light onto the desired zone of the cornea in order to ablate a lamina of material of the desired dimensions; and, a series of diaphragms and screens for obscuring varying portions of the zone of the cornea undergoing ablation in order to effect differential irradiation of the corneal surface.