Measuring three dimensions of eye movement in dynamic situations by means of videooculography

A primary function of the vestibular system is the stabilisation of the eye during head movement. Consequently, evaluation of reflex eye movements represents an essential means to both clinical diagnosis and researching of the vestibular function. Movements in the eye can be resolved into three orthogonal components, i.e. horizontal, vertical and torsional. As an improvement on most current techniques, which provide only measurement of the horizontal and vertical components, videooculography (VOG) facilitates non-invasive measurement of all three of the defined components. To date, only the scleral coil technique, which involves the semi-invasive placement of coil rings onto the bulbi, yields a continuous measure of eye torsion. Employment of suitable solid-state devices permit the integration of a compact, high resolution video recording system. In the basic configuration, eye movements can be observed and simultaneously recorded for later analysis or documentation. The video images of the eye are obtained by means of a miniaturised CCD video sensor mounted on a light-occluding mask. Image processing of the acquired video images determines horizontal and vertical coordinates of eye position online. Ocular torsion, as reflected by the rotation of the natural iris, is measured for each video frame. The VOG algorithm has been implemented on a PC based workstation, which permits online observation, recording and evaluation of eye movements. In addition, the technique has found clinical application as a portable eye-movement observation and recording system, allowing bedside examination and recording of transient symptoms. Preliminary results from various studies, including the objective evaluation of positional nystagmus (BPPN), are presented.