Vertical Vestibulo-Ocular Reflex, Smooth Pursuit and Eye-Head Tracking Dysfunction in Internuclear Ophthalmoplegia

Abstract

Vertical smooth eye movements were quantified by magnetic search coil oculography in 7 patients with internuclear ophthalmoplegia (INO), 4 bilateral and 3 unilateral, and compared with age-matched normal subjects. The upward and downward vestibulo-ocular reflex (VOR) had reduced gain and abnormal phase lag in both unilateral and bilateral INO during active head motion at frequencies from 0.25 to 2 Hz. The phase lag was attributed to disruption of vestibular eye velocity signals and relative preservation of eye position signals. Fixation of a stationary target enhanced smooth eye movement gain during vertical head motion but it remained subnormal. Vertical smooth pursuit gain was mildly reduced. All patients had normal gaze (eye plus head) gain when tracking with both the head and eyes despite defective cancellation of the vertical VOR; they employed high amplitude head tracking to compensate for the uncancelled VOR. Cancellation was more impaired than smooth pursuit. Dissociation between cancellation and ocular pursuit was also demonstrated by a model of VOR cancellation that uses measured pursuit gain with the head immobile to predict gaze gain of eye-head tracking. The model predicted eye-head tracking gain in normal subjects but not in patients with INO. The results indicate that the medial longitudinal fasciculi or neighbouring tegmental tracts convey bidirectional signals for vertical pursuit, cancellation, and vestibular smooth eye movements in man, and that smooth pursuit and cancellation of the VOR can be dissociated in INO.

Do the paramedian tract neurons in pons take a role as a vertical neural integrator in humans?

“…The lesion in our patient was extended to just ventral of the fourth ventricle dorsally and spread through the whole pons vertically. Both bilateral MLF [8,9] and the PMT cell groups [4] can be considered as possible structures of impaired vertical gaze holding in the pontine level. Because our patient had a unilateral INO, however, lesion in PMT cell groups might be the more possible cause of the vertical GEN.…”

Upbeat Nystagmus due to a Small Pontine Lesion: Evidence for the Existence of a Crossing Ventral Tegmental Tract

“…It should be noted that the MLF is probably and the BC possibly also involved in the transmission of upward excitatory vestibular signals [1,2,14] . However, whatever the actual role of the BC, it would appear that upward vestibular signal transmission depends on both the MLF and the CVTT, whereas downward vestibular signal transmission appears to depend only upon the MLF [2] .…”

Role of eye movement examination and subjective visual vertical in clinical evaluation of multiple sclerosis

“…Although many studies have confirmed the validity of these tests by making precise measurements of eye movements ( Fig. 1) [6,7,15,24,28], they remain clinical methods that are easy to elicit and interpret, provided the examiner understands what to look for.…”