ABSTRACT.Purpose: An improved induction-based impact method for measuring intraocular pressure is presented. Methods: A light probe containing a permanent magnet is launched towards the eye using a solenoid. The probe hits the eye and bounces back. The same solenoid, inside which the probe moves, is used to detect the movement and impact of the probe, because the moving magnet induces voltage in the solenoid. In the clinical study, the Goldmann applanation tonometer was used as a standard. Handheld and fixed tonometers were also compared by means of measurements in pressurized pig eyes. Results: At a low intraocular pressure (IOP), there is a longer impact time than at a high IOP. A handheld tonometer causes more variation in impact times, especially at low intraocular pressure (IOP), than a fixed tonometer. Conclusions: The new induction-based impact method can be used to measure IOP. When a fixed tonometer is used, there is less variation in impact times.

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The I/I tonometer can be used for noninvasive, in vivo IOP measurement in mouse eyes. The availability of an easy-to-use, reliable tonometer for IOP measurements in mice will allow more extensive use of the mouse as a model for glaucoma.

A new electromechanical method to measure intraocular pressure is presented. A light probe was made to collide with an eye (cornea or sclera) and to bounce back. The impact was registered by an acceleration sensor or the duration of contact with the eye was measured using the phenomenon of the electrical conductivity of biological objects. Laboratory experiments were carried out using pig eyes pressurized with water leveled to different heights. Preliminary clinical trials were carried out comparing the values obtained with those of the Goldmann applanation tonometer. The time of contact and the deceleration time decreases and the deceleration maximum increases in proportion with IOP. A new kind of tonometer can be constructed based on this principle. Measurement can be performed to cornea or sclera without an anesthetic drop. Further study is required to evaluate the accuracy and usefulness of this method.

Measurement of IOP with the Rebound tonometer without an anesthetic is a rapid and well-tolerated procedure. IOP readings of the two tonometers were within +/-1 mmHg in 52.5% of the measurements and within +/-2 mmHg in 71.7% of the measurements.