Low intensity galvanic vestibulo-ocular reflex in normal subjects

An electrical stimulation in man applied between the two mastoids could fac ilitate the distinction between labyrinthine and retrolabyrinthine lesions by stimulating directly the primary vestibular afferences. However, for thi s test to be really effective in current medical practice, the results obta ined in normal subjects must be symmetrical and reproducible one day to ano ther. The ocular responses induced by a constant electrical stimulation of 2.5 mA, applied between the two mastoids for 30 s (electrically evoked vest ibule-ocular reflex [EVOR]), in one direction and the other, were quantifie d in ten healthy subjects. Each subject was studied in two different sessio ns separated by 1 week. Horizontal eye movements were recorded in darkness by an infrared light reflection eye-tracking system. Slow-phase velocity an d nystagmus frequency were about 20% higher when the cathode was on the rig ht mastoid than when it was on the left mastoid. This directional preponder ance (DP) displayed large individual differences between the two sessions. The reproducibility of the reflectivity (mean of right and left EVOR) was h igh (r about 0.8). The weak reproducibility of the DP makes the EVOR at wea k intensity inadequate to evaluate unilateral vestibular hypofunction. On t he other hand, because of the high reproducibility of reflectivity, the EVO R should be effective in detecting bilateral vestibular hypofunction. Moreo ver, because of the weak intensity of stimulation, no local anaesthesia is needed so the manoeuvre is easy to repeat in case of chronic diseases. (C) 1998 Elsevier, Paris.