Gain and Delay of Human Vestibulo-ocular Reflexes to Oscillation and Steps of the Head by a Reactive Torque Helmet

Abstract

Vestibulo-ocular reflexes (VOR) were evaluated with a reactive torque helmet that imposed high-frequency oscillation (2-20 Hz) or step displacements of the head in the horizontal plane. The present paper describes the results in patients with vestibular deficiencies (labyrinthine defective; LD); experimental and analytical techniques and results for normal subjects were described in Part 1 of this paper. The patient groups included: total unilateral LD (related to acoustic neuroma; n = 40); severe (clinically total) bilateral LD (n = 7); bilateral hyporeflexia (n = 14); unilateral hyporeflexia (n = 11); and patients with LD phenomena that had subsided (n = 3). Helmet-induced head steps provided the most specific information. Characteristically, gain was lowered in one direction or both directions after unilateral or bilateral vestibular lesions, respectively; in general, the magnitude of the gain reduction correlated well with the degree of complaints and disability. Surprisingly, delay was systematically prolonged (up to several tens of milliseconds) in all groups of subjects with manifest vestibular pathology. These results suggest that the determination of delay, in addition to gain of the VOR, is feasible and important in the evaluation of vestibular function. The results of head oscillation generally supported the results for steps, but were somewhat less specific. The responses to manually generated head steps roughly agreed with those to helmet-induced steps, but because of the non-uniform acceleration they allowed a less exact analysis of VOR function.

Motorized Head Impulse Rotator for Horizontal Vestibulo-ocular Reflex

“…We achieved results comparable to those of the magnetic search coil techniques used previously. [5][6][7] In addition, our method is noninvasive, safe, repeatable, and easy to perform for the operator and the subject. Our method demands no special effort from the patients, and it allows fast measurement of horizontal vestibulo-ocular reflex function in a clinical setting.…”

“…They achieved well-controlled transient horizontal head impulses with a mean acceleration of 770°/s 2 and velocities of 50°/s to 100°/s during their analysis window. 6,7 This velocity range is close to the velocity saturation seen in patients with vestibular complaints, which might limit the usefulness of the equipment. 8 We constructed our head impulse rotator to accomplish stimulation magnitudes well above this velocity saturation range and to better control the stimulus intensity.…”

A Signal Analysis Technique of Vestibulo-Ocular Reflex Stimulated with Impulsive Head Movements

“…1,14,15,33,46,47 Gain and latency attributes are important for VOR eye movements. Gain is defined as a ratio based on amplitude values (angles from the middle point of the gaze) during a VOR eye movement and its corresponding stimulation.…”

“…Tabak et al 46 applied stimulation acceleration of 1000 • /s 2 as sufficient to reveal vestibulo-ocular reflex deficiencies. Stimulation length should then be slightly longer than 0.100 s to facilitate signal processing and analysis.…”

“…Vestibulo-ocular reflexes stimulated with controlled impulsive head movements were recently introduced. 46,47 A subject's head is mechanically rotated from right to left and back or vice versa. When a subject does not know the moment of the beginning of a stimulus movement, this test is unpredictable from the subject's viewpoint.…”