To determine the lesions and the lateralization in patients with Walle
nberg's syndrome, visually-guided eye movements were quantitatively an
alysed and these findings were compared with a lesioned site as reveal
ed by magnetic resonance imaging (MRI). The 8 patients could be clearl
y classified into two subgroups based on the functional test of eye mo
vements. In 4 patients, optokinetic nystagmus (OKN), pursuit eye movem
ents and fixation-suppression of caloric nystagmus (FS), utilizing the
slow phase velocity as a parameter, were impaired toward the lesioned
side in the medulla. In the remaining 4 patients, OKN and pursuit eye
movements were impaired toward the side contralateral to the lesion,
whereas FS toward the lesioned side, indicating a lesion affecting not
only the medulla but also the inferior peduncle and/or the cerebellum
. Therefore, the functional visually-guided eye movements can provide
a useful test battery with which to detect the lesion site in Wallenbe
rg's syndrome.