Smooth pursuit eye movements in epileptics under antiepileptic medication

1) Smooth pursuit eye movements (SPEM) were recorded in 18 normal, 20 schizophrenic and 50 epileptic subjects. Most of the schizophrenic and epileptic subjects were under medication, antipsychotic drugs in the former and antiepileptic drugs in the latter. 2) In schizophrenics and epileptics, rate of the saccadic component in SPEM was higher than that of normal controls. The rate of large amplitude saccades was higher in epileptics than in schizophrenics. 3) Though small amplitude saccades were usually superimposed on SPEM in schizophrenic patients, both large and small amplitude saccades superimposed irregularly on the smooth tracking curve were observed in epileptics, and overshoots or undershoots were also seen frequently. 4) SPEM disorder in epileptics was observed in more than half of patients receiving antiepileptic medication, especially in patients with a long period of treatment. SPEM disorder in epileptics tended to occur frequently in patients who received phenytoin in doses higher than a certain level; i.e. approximately 150 mg per day for a long period of time. 5) It is conceivable that the SPEM disorder represents a latent or subclinical cerebellar dysfunction due to phenytoin medication. It is suggested that the SPEM measurement is a useful tool to find out subclinical side effects of antiepileptic drug in the treatment of epilepsy.