Lay summary
The long-term goal of this research is to better understand diseases of the ocular motor system in humans and to assess potential treatments. The focus of interest is on the three-dimensional (horizontal, vertical, torsional) kinematical properties of ocular rotations. Specifically, we explore eye movements in patients with peripheral vestibular lesions, cerebellar disorders, and strabismus as well as in healthy human subjects. As a first approximation, the linear vestibulo-ocular reflex (LVOR) can be divided into a mechanism that attempts to stabilize the fovea on a space-fixed target (compensatory or translation LVOR, dependent on target distance) and a mechanism that attempts to stabilize the retina relative to gravity (orienting or tilt LVOR). - (1) We will analyze whether or not ocular roll evoked by a reorientation of the gravito-intertial force vector (GIFV) differs from ocular roll evoked by changing the magnitude of the GIFV. (2) We will explore whether otolith-driven cyclovergence is an inherent property of the ocular motor response to interaural acceleration or whether it is due to a separate otolith-ocular reflex elicited by acceleration along the head longitudinal axis. (3) In patients with cerebellar downbeat nystagmus, we will analyze whether acceleration along the nasooccipital axis evokes vertical eye movements greater than in healthy subjects. Such a response could explain why, in cerebellar patients, static head pitch, which reorients the gravity vector towards the naso-occipital axis, leads to downward ocular drift in supine position and upward ocular drift in prone position. - This research uses the latest techniques for vestibular stimulation (hexapod motion simulator, motorized multi-axes turntable) and eye-head movement recordings (dual search coil technique). We will elucidate major mechanisms of orienting (i.e. tilt) otolith-ocular reflexes in humans and how they are affected by peripheral and central vestibular lesions. These insights will help to better understand balance disorders in patients and eventually improve their treatment.