A replaceable cornea contactor for an eye examining instrument is made to be discarded after each use. A bendable tab molded on the cornea contactor is deformed by a strain gauge as the cornea contactor is inserted into a cornea contactor holder, and a signal from the strain gauge is used to verify that a previously unused cornea contactor has been inserted into the holder. A microprocessor is programmed to recognize the signal produced by initial deformation of the cornea contactor tab so as to proceed with an eye examination only after receiving the strain gauge signal verifying that a previously unused cornea contactor has been inserted.