Simulation of pathological ocular counter-roll and skew-torsion by a 3-D mathematical model.

A basic version of a 3-D mathematical model for simulation of otolithic control of binocular static eye position was extended by introducting excitatory commissural fibers between the vestibular nuclei, and physiological non-linearities: the force-response relationship of utricular neurons and a quadratic relationship between eye muscle innervation and force. These modifications appeared to be necessary in order to simulate the gain asymmetry of ocular counter-roll to lateral head tilt in patients with unilateral utricular loss. The current model can adequately simulate skew-torsion in patients with unilateral utricular loss, lesions of the vestibular nuclei, and central graviceptive pathway lesions. The direction of simulated skew-torsion corresponds satisfactorily to data from normals and patients with acute vestibular loss. The relatively low values of predicted eye deviations for peripheral vestibular lesions suggest that part of the effects seen in patients is caused by affection of the semicircular canals.