The one-and-a-half syndrome is characterised by a lateral gaze palsy in one 
direction and internuclear ophthalmoplegia in the other. It is due to a 
unilateral lesion of the dorsal pontine tegmentum, involving the ipsilateral 
paramedian pontine reticular formation, internuclear fibres of the ipsilateral 
medical longitudinal fasciculus and, usually, the abducens nucleus. The main 
causes of this rare syndrome are stroke and multiple sclerosis. Few cases have 
been reported since the introduction of MRI. Our aim was to examine 
clinicoradiological correlations in six patients with a one-and-a-half syndrome 
due to a stroke. Ophthalmological symptoms were diplopia, oscillopsia or blurred 
vision. Four patients had an associated facial nerve palsy, three a hemiparesis 
and one a unilateral hemihypoaesthesia. MRI revealed an infarct in the pons in 
all patients. The cause of the infarct was a basilar artery dissection in one 
patient, bilateral vertebral artery dissection in a second and unknown in the 
other four. All patients recovered within 2 days to 8 weeks. This study showed a 
good correlation between the site of the lesion (superior, inferior or extensive 
pontine ischaemia) and clinical deficits.