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Agnes M. F. Wong, Douglas Tweed, James A. Sharpe; Adaptive Neural Mechanism for Listing’s Law Revealed in Patients with Sixth Nerve Palsy. Invest. Ophthalmol. Vis. Sci. 2002;43(1):112-119.
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purpose. During fixation and saccades, human eye movements obey Listing’s law,
which specifies the torsional eye position for each combination of
horizontal and vertical eye positions. To study the mechanisms that
implement Listing’s law, the authors measured whether the law was
violated in peripheral and central unilateral sixth nerve palsy.
methods. Twenty patients with peripheral (13 chronic, 7 acute) sixth nerve
palsy, 7 patients with central sixth nerve palsy caused by
brainstem lesions, and 10 normal subjects were studied with scleral
search coils. With the head immobile, subjects made saccades to a
target that moved between straight ahead and eight eccentric positions.
At each target position, fixation was maintained for 3 seconds before
the next saccade. To quantify violations of Listing’s law, we measured
ocular torsion during fixation and during saccades, and compared it
with the torsion predicted by the law. The SD of the differences
between the predicted and measured torsion was called Listing
results. Patients with central sixth nerve palsy had abnormal ocular torsion in
both the paretic and nonparetic eyes, which violated Listing’s law.
During fixation, Listing deviation averaged 2.4° in the paretic eye
and 1.7° in the nonparetic eye, compared with 0.8° in normal
control subjects (P < 0.05). During saccades, the
Listing deviation averaged 2.7° in the paretic eye, and 1.6° in the
nonparetic eye, compared with 0.8° in normal control eyes
(P < 0.05). Donders’ law was also violated in
both eyes of patients with central sixth nerve palsy. They showed an
abnormally wide range of ocular torsion in any given gaze direction. In
contrast, patients with acute peripheral palsy had abnormal ocular
torsion only in the paretic eye. Listing deviation of the paretic eye
averaged 2.3° during fixation and 3.2° during saccades
(P < 0.05). Donders’ law was obeyed in acute
peripheral palsy. Patients with chronic peripheral sixth nerve palsy
obeyed Listing’s and Donders’ laws during both fixation and saccades.
conclusions. Patients with central unilateral sixth nerve palsy have abnormal ocular
torsion in both eyes, demonstrating that brainstem circuits
normally participate in the maintenance of Listing’s law. Eye
movements in patients with acute peripheral sixth nerve palsy violate
Listing’s law, whereas those in patients with chronic peripheral palsy
obey it, indicating that neural adaptation can restore Listing’s law,
even when the eye muscle remains abnormal.
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