Short vestibule-ocular reflex time constants associated with oculomotor pathology in multiple sclerosis

Abstract

Significantly short vestibulo-ocular reflex (VOR) time constants were found in significant high numbers in patients with multiple sclerosis who had oculomotor dysfunction, especially when this dysfunction comprised both the smooth pursuit/optokinetic and the saccadic systems. Some time constants were in the range of 2.5–6 s, i.e. shorter than the presumed time constant of the primary afferent canal neuron. Increase in oculomotor impairment was accompanied by a decrease in time constants in some patients, whereas others showed a combined renormalization of previously disturbed oculomotor function and short time constants. Significantly high numbers of combinations of asymmetry in oculomotor dysfunction and a directional preponderance in time constant were observed, with the shorter time constant on the side of the (more severe) defect.

Key Words:

• vestibulo-ocular reflex (VOR)
• smooth pursuit
• optokinetic nystagmus
• saccades
• velocity storage mechanism