 |
 |
5 |
 |
|
fixation revealed mostly rightward directed square-wave jerks. They had a
mean amplitude of
0.5
degrees, a mean inter-saccadic interval of 185 msec,
and a variable frequency ranging from
0.5
to
2
Hz with intermittent 3 to 4
Hz bursts. These square-wave jerks became more prevalent as testing con-
tinued. Saccadic tracking (io deg amplitude,
5
deg left and right of midline;
temporal randomization) revealed highly variable metrics, at times exhibit-
ing:
(i)
large
(0.5
to
2
deg) dynamic overshoots on rightward gaze;
(2)
large
(0.5
to
2
deg) glissadic overshoots on both rightward and
leftward gaze,
sometimes following a rightward directed static overshoot; (3) hypometric
saccades to the right and left requiring a subsequent one- to two-degree cor-
rective saccade
(200
msec later) to attain accurate foveation; and (4)
normometric saccades to the left and right.
Mean saccadic latencies were within normal limits
(195
msec) for both
leftward and rightward directed saccades. Square-wave jerks of
0.5
degree
were intermittently present, at times occurring in couplets, during the inter-
saccadic fixation periods. Saccades had normal peak velocities in both direc-
tions. During constant velocity pursuit (io amplitude,
5
deg left and right of
midline), the patient easily tracked targets ranging in frequency
0.2
to
2
Hz.
Pursuit gain
was normal
(0.93
to the left and o.88 to the right). There was
evidence of prediction to the right but not to the left, with a large initial one-
to three-degree saccade embedded in each response in both directions. To
the left this consisted of a square-wave jerk, whereas to the right it consisted
of a single saccade. Versional movements were similar under both monocu-
lar and binocular viewing conditions. When asked to perform symmetrical
(midline) vergence tracking of a pencil point moving slowly
(i.e.,
ramp-like)
between
57
and
17
cm, the patient easily followed the target in both the con-
vergent and divergent directions. However, numerous rightward directed
square-wave jerks of
0.5
degree amplitude with a frequency of
i
Hz were
always present.
Fig. 3.
Representative objective eye
movement recordings in our subject
during binocular viewing. A.
Fixation, B. Saccades,
C. Pursuit, D.
Vergence. In the position traces,
upward deflections represented
leftward movement and downward
deflections represented nghtward
movement. Time markers represent
seconds.
Guillain-Barré syndrome
253
|
|
|
5 |
|