Disorder of Smooth Pursuit Eye Movement as a Side Effect of Antiepileptic Drugs

Smooth pursuit eye movements (SPEM) were recorded in 18 normal and 84 epileptic subjects. In epileptics, rate of saccades in SPEM was higher than that of normal controls. Seventy-five of our 84 epileptic patients had been taking one to several kinds of antiepileptic drugs. It was demonstrated that remarkable disorder of SPEM was observable in more than half of epileptic patients receiving antiepileptic medication. The effect of antiepileptic drugs was supposed to be a cause of the SPEM disorder, because no remarkable saccades were observed in epileptics who were not receiving antiepileptic medication and SPEM disorder in epileptic was seen frequently in patients with a long period of treatment. With regard to phenytoin, most of the SPEM disorder in epileptics was observed in patients who had been given phenytoin more than 150mg a day for a long period of time. Although it was suggested that high serum concentration of phenytoin or phenobarbital contributed to a part of SPEM disorder, in most of SPEM disorder in epileptics, there was no correlation between serum concentration of antiepileptic drugs and rate of saccades. It was also demonstrated that there was a close relationship between conjugate lateral gaze nystagmus and SPEM disorder in epileptics. It is conceivable that the SPEM disorder in epileptics represents a latent or subclinical chronic cerebellar dysfunction due to phenytoin medication. It is suggested that the SPEM measurement is a useful tool to find out subclinical side effects of some antiepileptic drugs in the treatment of epilepsy.