Abstract: A tonometer capable of measuring systolic or ocular pulse pressure (OPP) can be used to examine eyes of a patient to measure whether OPP or ocular blood flow (OBF) is sub-normal to one or both eyes. This can serve as an indication of a possible constriction of blood flow in arteries leading not only to the eyes, but to the brain and other regions above the neck. Any such sub-normal measure can then indicate that further investigation of blood flow in carotid and other arteries is appropriate.

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