Conventionally, IOP (cf. Glossary) is measured by applanation of the cornea, e.g. by the Goldman applanometer. Devices of this type exert pressure centrally on the cornea up to a predefined applanation and measure the force required. However, due to the central impact on the cornea, a significant dependence on the curvature of the cornea and its stiffness exists.
Recently, pressure sensors have been developed measuring the pressure or force exerted in a peripheral region of the cornea. One such sensor is described in British patent application 1017637.8 in the name of the University of Dundee et al. which is not yet published. The pressure sensor is a contact lens with a circumferentially embedded pressure sensor. The pressure sensor bears toward the cornea an elevation. If the lid closes over the contact lens, it is flattened and the elevations are pressed on the cornea. On the basis of a suitable calibration, which accounts for individual mechanical properties of the eye and the lid, the IOP can be monitored over extended periods, e.g. 24 hours.
The front side of the sensor portion, i.e. opposite the cornea, may be constituted by a material significantly stiffer than the cornea so that the pressure of the lid is transmitted to the sensor without significant deterioration.
Generally, the sensor is of the type of a variable capacitor coupled to an inductance to constitute a resonance circuit. The inductance serves as the antenna so that the resonance frequency can be wirelessly determined.
For example, an eyeglass frame may be provided with a suitable antenna and the emitter electronics may be implemented in the frame. Thereby, monitoring is possible with only a minimum impairment to the monitored person.
However, the requirement of an adaptation and periodical recalibration of the system remains, which is burdensome and expensive.