Use of a Piezo-Accelerometer in Studying Eye Dynamics

Abstract

A small cantilever-type piezoelectric accelerometer has been fixed to a contact lens. By means of one or two electrical integrations of the amplified output voltage, angular acceleration, velocity, or displacement of the moving eye can be measured as functions of time. The sensitivity is high enough to record involuntary saccades and tremor during fixation; the bandwidth of the system under these conditions is 200 cps. The high sensitivity is maintained for all positions of the eye, so that during saccades and other fast eye movements, the fine detail, particularly of the small overshoots, can be examined.For study of the characteristics of the extraocular muscle–eyeball system, sinusoidal or transient eye movements caused by applying vibrational or steplike forces to the eye are recorded. These forces are applied by the action of an electromagnet on a piece of magnetic material fixed to the contact lens. Forced eye movements are also induced by applying either steady vibrations or impulsive forces to the head. Two recording accelerometers are then used, one is on the contact lens, and the second is fixed to a bite bar. Experiments have been made with human subjects and with dogs. Typical recordings are discussed.