The cervico-ocular reflex in normal subjects and patients with absent vestibular function.

The role of the cervico-ocular reflex (COR) has been studied in 12 patients with absent vestibular function and 13 normal subjects. Ramp and sinusoidal displacement stimuli were applied with trunk on head and head on trunk movements. In all patients, trunk on head movements evoked a marked slow-phase compensatory COR while in normal subjects it was weak and variable in direction. Fast components of the COR induced gaze shifts in the direction of the relative head movement ('anticompensatory' direction) which could be suppressed by imagining an earth fixed targed. No tonic component could be identified instead, in the case of ramp stimuli, a residual eye deviation was noted which was significantly enhanced in the patients and resulted from activity dynamically generated during the course of the trunk movement and not from its final angular displacement. Head on trunk ramp displacements in the dark evoked initial anticompensatory saccades followed by slow compensatory components, a pattern of eye movements remarkably similar to that seen during active head-eye target seeking. Thus, in the absence of labyrinthine function, the COR appears to take on the role of the vestibulo-ocular reflex in head-eye coordination in the initiation of the anticompensatory saccade which takes the eyes in the direction of the target, and the generation of the subsequent slow compensatory eye movements. Central pre-programming, as revealed by comparing the effect of different instructions and active versus passive neck-induced eye movements, has a profound influence on COR functioning.