This paper discusses a method to carry out optical interferometric measurements for the surface roughness of spheres like a biomedical application to an artificial joint, using Michelson interferometric microscope with digital image processing and a computational system to process two interferograms. The paper proposes an algorithm on the calculation of the standard least squave circles and arc from each fringe edges and the meathods to obtain the profile departures from reference mean lines and the surface roughness parameters.