Background - Impairment of vertical gaze has been attributed to lesion
s involving the neural structures at the mesodiencephalic revel. Objec
tive - Eye movements were studied in a patient with a unilateral param
edian thalamic infarction documented by MRI. Case description - A 63-y
ear-old mall presented 3 days after sudden onset vertical diplopia and
hypersomnia. Eye movements were studied with electro-oculography and
revealed impairment of vertical saccades with sparing of the vertical
vestibulo-ocular reflex, vertical pursuit, Bell's phenomenon and verti
cal optokinetic nystagmus. MRI scan revealed a circular zone of altere
d signal intensity. suggesting infarction, In the paramedian ventral p
art of the right thalamus. Conclusions - This case demonstrates that a
unilateral lesion mainly affecting the dorsomedial nucleus of the tha
lamus can result in selective impairment of vertical saccades and sugg
ests that the corticofugal fibers mediating vertical saccades traverse
in the medial thalamus en route to the rostral midbrain.