SACCADIC JITTER IS A QUANTITATIVE OCULAR SIGN IN MYASTHENIA-GRAVIS

Purpose. To examine the variability of saccadic peak-velocity amplitud e relationships in myasthenic and nonmyasthenic ocular palsies. Method s. The authors measured centrifugal saccades in nine patients with mya sthenia gravis, nine patients with proven nonmyasthenic ocular palsies , and three normal subjects. Patients made repetitive saccades for 8 m inutes. Saccades were analyzed at the start of the task, after 3 minut es of the task (fatigue), and at 1 minute after edrophonium. The autho rs fitted an exponential function to individual data and averages for amplitude bins and calculated the root mean square error of the curves . They then subtracted the root mean square error of curves fitted to bin averages from that of curves fitted to individual saccades: The re sult was an index of the variability of saccadic peak velocity, which they called saccadic jitter. Results. Compared to those without myasth enia, the saccades of patients with myasthenia showed more variability in the initial and the fatigue periods. The change induced by edropho nium did not distinguish between the groups. Conclusions. Signal detec tion analysis indicated that saccadic jitter has little value as a scr eening tool but is a useful diagnostic sign in 42% of myasthenic sacca dic analyses.