Three-dimensional Rotational Axis Analysis of Eye Movement as Clinical Applications

Abstract

We developed a new video-oculography (VOG) system that can facilitate analysis of the axis angle, rotation vector or quaternions of eye movements. The axis angle, rotation vector, and quaternions measure a single rotation from a chosen reference position to the current eye position. Using the axis angle, rotation vector, or quaternions, we can calculate the axis around which the eye rotates and the angular velocity around the axis. In this review, we show how we utilize the analysis of eye rotational axis and eye velocity around the axis in clinical applications. By calculating the axis of positional nystagmus in benign paroxysmal positional vertigo (BPPV) patients, we can identify the affected lesion in the semicircular canals. Posterior semicircular canal (PSCC) type of BPPV causes positional nystagmus in which the rotational axis is perpendicular to the plane of the PSCC or pure torsional axis. Horizontal semicircular canal (HSCC) type of BPPV (H-BPPV) causes positional nystagmus in which the rotational axis is perpendicular to the plane of the HSCC. A dramatic change in the eye angular velocity and time constant of nystagmus is seen at the transitional period when cupulolithiasis changes to canalolithiasis in a patient with H-BPPV. Anterior semicircular canal (ASCC) type of BPPV causes positional nystagmus in which the eye rotational axis is perpendicular to the plane of the ASCC. BPPV due to the simultaneous involvement of both horizontal and posterior semicircular canals has two rotational axes; first, it is perpendicular to the plane of the PSCC, then, it is perpendicular to the plane of the HSCC. By calculating the eye angular velocity around the axis, we can show that the gain of the vestibulo-ocular reflex around the eye rotational axis can be calculated both when HSCCs are mainly stimulated and when vertical semicircular canals are mainly stimulated.