Abstract
In this study, variation of corneal vibration by changing the excitation frequency of the cornea excitation type tonometer and the influence of frequency change on intraocular pressure estimation has been studied. Since the commonly used tonometer adopt the measurement method applying a large external force to the cornea, the subjects feel uncomfortable at the time of measurement. Therefore, periodic intraocular pressure measurement tends not to be favoured. A cornea excitation type tonometer has been proposed in order to reduce the stress given to a subject. It is a characteristic of this tonometer that the cornea is excited at a frequency below the audible range without contact and the intraocular pressure is estimated from the low frequency component of the vibration. A point concentration type parametric speaker in which ultrasonic elements are arranged in a curved manner is used as a vibration source, and low frequency excitation force is obtained by modulating the carrier wave with a frequency below the audible range. In the previous study, the excitation frequency was set to 10 Hz, but accurate intraocular pressure could not be estimated. Especially at high intraocular pressure, the corneal amplitude is small and it is difficult to discriminate between sensor noise and corneal amplitude, so the accuracy of intraocular pressure estimation has remarkably deteriorated. Therefore, in this study, first, changes in the corneal vibration when the frequency of the excitation force is changed were investigated. As a result, it was found that the SN ratio improves when excited at 2 Hz lower than in the previous study. Next, it was investigated whether intraocular pressure can be estimated with features other than the periodic amplitude of the cornea in the corneal vibration waveform. As a result, it was suggested that the eye pressure can be estimated by paying attention to the DC component of the corneal displacement.
