Oscillopsia of peripheral vestibular origin:Central and Cervical Compensatory Mechanisms

Abstract

Eight patients with absent vestibular function categorized into four grades according to the disability they suffered from oscillopsia have been studied with a view to correlating its severity with the development of gaze stabilizing compensatory mechanisms. Eye movements were recorded while the following sinusoidal rotational stimuli were delivered: 1) trunk on head oscillation in the dark (COR); 2) head on trunk oscillation in the dark; 3) head on trunk and whole body (head and trunk) oscillation in the light in the presence of optic fixation. The COR was potentiated in all the patients regardless of their clinical status. Velocity gains (peak slow phase eye velocity/peak head velocity) during whole body rotation were significantly lower than head on trunk gains in the light in the better compensated patients. Since in the absence of vestibular function whole body rotation involves only the otokinetic system (OKN), this finding implies a depression of the OKN in these patients which can be corrected during head on trunk movements by virtue of a dynamic input from the neck. The results suggest that the processes of recovery from oscillopsia are dependent, in the main, upon the development of central mechanisms by means of which undesirable image movement across the retina is perceptually suppressed. Depression of OKN may be secondary to this perceptual rearrangement.

Recovery of Gaze Disturbance in Bilateral Labyrinthine Loss

“…Furthermore, he never com plained of oscillopsia upon head rotation and upright locomotion [13]. Therefore, gaze disturbance in this patient seems to have been compensated for by both adaptation of the central perceptive mechanism [11] and activation of the optokinetic system through daily head movements in childhood. Passive rotation may not have stimulated the strate gies characteristic of congenital labyrinthine lesions.…”

“…In man, gaze disturbance in unilateral lesions recovers within 1 year in accordance with a decreased imbalance of vestibulo-ocular reflex (VOR) accomplished mainly by an increase in VOR gain upon rotation to the affected side [7], Although gaze disturbance in bilateral lesions is hard to be compensated, the degree of oscillopsia markedly varies among different subjects [8,9,11] and perceptually becomes less with time [12], Many different strategies have been proposed: cervico-ocular reflex [2][3][4][5]9], central preprogramming [2][3][4][5], substitution by vision [3,9], perceptual ad aptation at the higher cortex [3], plastic change of the VOR [7,8], recalibration of the saccade, and restriction of head move ments [2,4,5],…”

Der beidseitige Vestibularisausfall

“…Kompensationsmechanismen bei fehlender Blickstabilisierung unter schnellen Kopfbewegungen nach Wegfall des VOR angenommen [4,5,9,13].…”

“…sowie zentrale Mechanismen der Unterdrückung bewegter Netzhautabbildungen ("retinal slip") bei denen dann nur während ruhiger, bewegungsarmer Phasen visuelle Informationen an das Gehirn weitergeleitet werden [4,5,9,13]. Möglicherweise sind aber auch erlernte Vermeidungsstrategien mit der Durchführung langsamerer Kopfbewegungen, bei denen die oben genannten Kompensationsmechanismen physiologischerweise besser greifen, von Bedeutung [3,4].…”

“…Möglicherweise sind aber auch erlernte Vermeidungsstrategien mit der Durchführung langsamerer Kopfbewegungen, bei denen die oben genannten Kompensationsmechanismen physiologischerweise besser greifen, von Bedeutung [3,4]. Der Begriff der Kompensation sollte somit in diesem Zusammenhang nur zurückhaltend Verwendung finden, da sich eine wirkliche zentrale Kompensation, wie bei dem einseitigen Labyrinthausfall, bisher nur für die Zunahme des COR nachweisen ließ [5,13].…”