Effects of edrophonium on saccadic velocity in normal subjects and myasthenic and nonmyasthenic ocular palsies.

We measured saccadic peak velocities in 8 patients with myasthenia gravis, 9 patients with proven nonmyasthenic ocular palsies, and 3 controls. Patients followed a target moving to and from primary position at 1-second intervals for 8 minutes. We measured the amplitudes and velocities of centrifugal saccades at the start of the task, after 3 minutes of the task (fatigue) and 1 minute after receiving IV edrophonium. The effects of fatigue, though prominent in some myasthenic patients, did not distinguish between the groups. However, edrophonium increased saccadic peak velocities in myasthenic patients but decreased them in both controls and nonmyasthenic patients. Analysis of saccades by amplitude bins showed that these changes in peak velocity reflected shifts in the velocity-amplitude relationship.