Corneal irregularities can create conditions in which monocular diplopia, “ghost images,” and multiple images of various types occur, thus degrading vision. For these secondary images to occur, corneal irregularities must create areas which form: (1) images which are displaced from the primary image; (2) sufficiently focused images; and (3) images which have sufficient contrast to be noticed in the presence of the primary image. Criteria necessary to satisfy these three conditions using measurable data are developed. The concept of a differential deflection field is introduced, and a method to create this field using corneal topography data is developed. It is shown how to use differential deflection field data to assess if conditions necessary for creating secondary images will occur in cases of corneal distortion.