Edrophonium-induced macrosaccadic oscillations in myasthenia gravis

In a myasthenia gravis patient with profound ophthalmoplegia who was given edrophonium during forward fixation or horizontal/vertical saccades, horizontal macrosaccadic oscillations occurred that were conjugate, 2 to 3 Hz, and of peak-to-peak amplitude up to 50 degrees. The intersaccadic interval averaged 129.5 msec as measured by electro-oculography. Eye closure or the use of Frenzel goggles markedly reduced the amplitude and frequency of the macrosaccadic oscillations. This short latency is similar to that of a corrective saccade, and suggests that edrophonium induces macrosaccadic oscillations through a non-visually guided reflex saccade by temporarily unmasking the adaptively increased saccadic gain to overcome myasthenic ocular paresis.