The characteristics and mechanisms of visual disturbance associated with anticonvulsant therapy.

Eight epileptic patients receiving anticonvulsants had recurrent visual disturbances in the form of diplopia and oscillopsia in the horizontal or vertical planes. The symptoms could be ascribed to impaired vergence mechanisms, vertical nystagmus, or abnormalities of the vestibulo-ocular reflex. Other eye movements, such as pursuit and gaze-holding, were also affected, but did not lead to complaints. Episodes of visual disturbance were often preceded by prodromes of ocular or systemic discomfort, after which oscillopsia or diplopia evolve rapidly. The symptomatology was stereotyped but unique for each patient and may reflect idiosyncratic susceptibility to the ocular motor side effects of anticonvulsants. Six of the 8 patients were taking carbamazepine and phenytoin in combination, which have similar effects on the ocular motor system.