'Saccadic jitter' is a quantitative ocular sign in myasthenia gravis.

PURPOSE To examine the variability of saccadic peak-velocity amplitude relationships in myasthenic and nonmyasthenic ocular palsies. METHODS The authors measured centrifugal saccades in nine patients with myasthenia gravis, nine patients with proven nonmyasthenic ocular palsies, and three normal subjects. Patients made repetitive saccades for 8 minutes. Saccades were analyzed at the start of the task, after 3 minutes of the task (fatigue), and at 1 minute after edrophonium. The authors 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 result was an index of the variability of saccadic peak velocity, which they called saccadic jitter. RESULTS Compared to those without myasthenia, the saccades of patients with myasthenia showed more variability in the initial and the fatigue periods. The change induced by edrophonium did not distinguish between the groups. CONCLUSIONS Signal detection analysis indicated that saccadic jitter has little value as a screening tool but is a useful diagnostic sign in 42% of myasthenic saccadic analyses.