the present invention provides extended depth of field to human eyes by modifying contact lenses , intraocular implants , and / or the surface of the eye itself . this may be accomplished by applying selected phase variations to these optical elements . the phase variations edf - code the wavefront and cause the optical transfer function to remain essentially constant within a range of distances from the in - focus position . this provides a coded image on the retina . the human brain decodes this coded image , resulting in an in - focus image over an increased depth of field .