Contactless measurement of contact lenses by topographical evaluation - using parallel and perpendicular collimated lens transmission and interferometry

A collimated light beam is passed through the lens perpendicular to and parallel to the optical axis. The outer shape of the lens is determined from the perpendicular beam shadow image. The radial thickness variation of the lens is determined from the local phase variation of the parallel beam on being passed through the lens. The phase variation is determined interferometrically. The internal shape of the lens is derived from the external shape and the radial thickness variation. The interferometric evaluation involves reference or object wave variation.