Jerk Nystagmus (Periodic Alternating Nystagmus)
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"This young man, with probable Multiple
Sclerosis, has a regular form of periodic alternating nystagmus. In
center gaze, a null period without nystagmus lasts about 30 seconds.
We are now beginning to see a right beating nystagmus. The amplitude
of the nystagmus gradually builds up and decreases over a period of
about 90 seconds. During the right beating nystagmus, the patient
experiences a horizontal oscillopsia. There is a small torsional
component to the nystagmus. While the nystagmus is beating to the
right, if the subject turns his face toward the right and places his
eyes in left gaze a null position can usually can be found in which
the oscillopsia and the nystagmus decreases. The amplitude of the
right beating nystagmus is decreasing, and there will be another null
period in center gaze in which the nystagmus is not present.
Oscillopsia is absent during the null period. A left beating
nystagmus will then begin to build in amplitude. It will also
gradually increase in size and then gradually decrease in amplitude
over a period of another 90 seconds. While the nystagmus is beating
toward the left, if the patient turns his face toward the left and
places the eyes in right gaze, another null zone of decreased
nystagmus and decreased oscillopsia is present."
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