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1 2007

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Noninvasive tonometry of intraocular pressure over a closed eyelid

Nakai M., Yoshizawa I., Fujita A., Takeda S., Yanasima K., Uchiyama A., Yanagisawa M.

Biocybernetics and Biomedical Engineering

2007

Vol. 27, no. 1-2

199-205

For more than 40 years, methods to measure intraocular pressure over a closed eyelid have been studied but without much success. The eyelid thickness varies among individuals, and this has been a major obstacle. This report presents our findings that vibrating the eyeball with an activator evokes a response depending on ocular pressure changes. The eyeball is vibrated with a ceramic transducer over the closed eyelid, and the value of the current flowing through the transducer is measured. The acoustic load of the transducer varies when it comes in contact with the object in which the internal pressure changes. As a result, the electrical impedance, in turn, varies in response to this load. Consequently, the current varies when an alternating voltage is applied to the transducer. Thus, intraocular pressure is converted from current value. A device based on this phenomenon was developed. It measures intraocular pressure within seconds, after being placed on the closed eyelid, and its weight is less than 55 g. The device was tested on 10 human eyes. The correlation coefficient in between our tonometer and the model routinely used in clinical use was about 0.93. Therefore, the new method is sufficiently accurate for clinical application.