The vertical and torsional vestibule-ocular reflexes (VOR) were invest
igated in 3 patients with surgical occlusion of the posterior semicirc
ular canal and 1 patient with singular neurectomy. for treatment of re
fractory paroxysmal positional vertigo. Stimuli comprised sinusoidal o
scillation in the coronal (''roll'') and sagittal (''pitch'') plane as
well as in two oblique planes intermediate between pitch in order to
stimulate left anterior + right posterior (LARP) and right anterior left posterior (RALP) canal pairs separately. One case with left side
BPPV was investigated pre and post-operatively. Depression of the vert
ical and torsional VOR gain was seen 1 week postoperatively when the o
ccluded canal was placed in the optimal plane for stimulation at 1 wee
k postoperatively and subsequently gradually recovered. Recordings in
other planes suggested that the contralateral posterior canal was also
hypofunctioning, a finding which may explain some residual gait unste
adiness in this case, The other 3 cases who were investigated postoper
atively all showed a decrease in downward VOR gain in the 'on' directi
on of the operated canal. The data indicate the specificity of the tes
t procedure and underline the prognostic value of comprehensive pre-op
erative vestibular assessment.