SACCADIC DURATION AND INTRASACCADIC FATIGUE IN MYASTHENIC AND NONMYASTHENIC OCULAR PALSIES

We measured the duration and amplitude of saccades in three normal sub jects, eight patients with myasthenia gravis, and eight patients with nonmyasthenic ocular palsies. Saccades were examined at the start of a repetitive saccade task, after 3 minutes of activity, and 1 minute af ter administration of edrophonium. The duration of saccades was prolon ged initially in both myasthenic and nonmyasthenic palsies. Activity d id not produce significant differences among the three groups in eithe r the slope of the duration-amplitude relationship or the predicted du rations of saccades of 5 degrees, 10 degrees, or 15 degrees. However, durations decreased in myasthenia but increased in nonmyasthenic palsi es after edrophonium. Much of this decrease in myasthenic saccadic dur ation was due to reduction in deceleration time, indicating resolution of intrasaccadic fatigue after edrophonium administration. However, t he relation of deceleration fraction (deceleration time divided by tot al duration) to total duration remained constant in all subject groups . Analysis of saccadic duration is a useful means of interpreting resp onses to edrophonium because it incorporates data from saccades of a w ide range of amplitudes into a linear relation between duration and am plitude.