The shearing interferometry is presented as an in vivo method for testing the stability of the tear film covering the contact lens. The material and quality of a contact lens and its correct fitting to the surface of cornea influence the stability of the tear film. By observation of the tear film distribution, the precise assessment of the quality of the contact lens surface can be performed. Moreover, the overused or damaged contact lens can be detected by the analysis of interferograms. In this study the following types of soft contact lenses were used: Dura Soft D3 (r equals 8,7 mm, r equals 8,4 mm), Medalist (r equals 8,7 mm) and Johnson and Johnson (r equals 8,8 mm). The contact lenses were placed on the patients' cornea. The 3 mW HeNe laser was used as the light source in shearing interferometer and the CCD camera for recording the interference images. The coherent light reflected from the surface of the contact lens covered with the tear film formed the interference pattern. The sequence of the obtained interferograms were recorded and then analyzed. The accuracy of the contact lens fitting can be estimated by the interferogram analysis. The examples of correct and incorrect fitting of the overused or damaged contact lenses are presented. The proposed method is noncontact, nondestructive and of the high accuracy.