A three-dimensional mapping system that measures the irregularities of an optical system (e.g., the human eye or a telescope lens); used in ophthalmology to detect refractive aberrations. Parallel light rays are directed toward the eye. If there are no aberrations, the returning light rays remain parallel. Any deviation indicates a defect that can alter the clarity of a visual image. Visual deficits caused by refractive aberration can be corrected by reshaping of the cornea.