The device of the invention comprises a protective cover for an optical device such as a gonioscope, capsulatomy lens, wide-angle lens, or any other lens having an eye-contacting surface. The cover is made sterile and disposable for allowing multiple use of the protected optical device. The cover is made from a soft material biologically acceptable for contact with a human eye. According to one aspect, the gonioscope protective cover is used merely for physically protecting the eye-contacting surface from direct contact with the eye. According to another aspect, the gonioscope protective cover combines the protective function with an optical function that changes the direction of light so that it becomes possible to observe the light emitted from the pupil at angles that are close to the angle of full internal reflection from the pupil medium.