Rapid eye movements in myasthenia gravis. II. Electro-oculographic analysis
R. D. Yee, D. G. Cogan, D. S. Zee, R. W. Baloh and V. Honrubia
Voluntary saccades were studied by electro-oculography in ten patients with
myasthenia gravis (MG) and in eight patients with other types of
ophthalmoplegia. Despite limited range of eye movements, maximum velocities
of 20 degree and 40 degree saccades in patients with MG were not
significantly different from those in normal individuals, whereas maximum
velocities in patients with other types of ophthalmoplegia were
significantly decreased. In some myasthenic patients, small amplitude
saccades were hypermetric and had high velocities, appearing clinically as
"quiver" movements characteristic of MG. In MG the preservation of saccades
with high initial velocities, even in the presence of severe
ophthalmoplegia, suggests that muscle fibers generating rapid movements
during saccades (twitch fibers) can be relatively spared when muscle fibers
responsible for maintenance of excentric gaze (tonic fibers) are severely
affected.
