Recovery from bilateral vestibular failure: implications for visual and cervico-ocular function.

Abstract

We report a patient who sustained severe bilateral labyrinthine lesions during Streptococcus suis meningitis but considerably recovered vestibular function over a 7 month period. This unique case allowed us to examine the cervico-ocular reflex (COR) and visual function at various levels of activity of his vestibular system. The slow phase COR, elicited by trunk oscillation (0.2 Hz) with the head earth-stationary, was negligible immediately after the acute vestibular loss but rose to a gain of 0.51 one month after. Seven months later, when vestibular function was improved, COR gain dropped to a gain of 0.15. Measurements of spatial visual function during whole body oscillation in the acute stage and after 6 months showed marked improvement which correlated entirely with VOR measurements in the dark and during optic fixation. This patient also showed the unique feature that, in the acute stage, eye movement gain and visual function were poorer during whole body motion than during identical visual target motion. These findings suggest that: i) the COR may be inhibited by the presence of vestibular signals, ii) spatial vision measurements provide accurate assessment of the patient's visual blur during head motion, and iii) the severe oscillopsia experienced by patients in the acute stage of vestibular loss may not only be due to the absence of the VOR; additional degradation in eye movements during head motion, perhaps arising from acutely distorted labyrinthine signals, may also play a part.