Development of noninvasive tonometer using resonance phenomenon

A tonometer is used to measure ocular pressure either by shooting a short blast of compressed air onto the cornea or by applying pressure directly to the cornea. At present, the tonometer is the primary instrument available for measuring ocular pressure. However, measuring ocular pressure by such means can either frighten or injure the patient. We propose an improved method of measuring ocular pressure in which the tonometer is applied over the patient's closed eyelid for several seconds. The sensor part of the newly developed tonometer contains a bimorph type transducer and weighs only 28.7 (g). When the sensor is placed on the eyelid and the transducer is vibrated by altering the applied voltage, the current flowing through the transducer changes in relation to the ocular pressure. Ocular pressure can thus be determined based on the current flowing through the system. During measurement, patients are generally unaware of the vibrations of the sensor and report no pain.