When Listing's plane stays fixed, horizontal lines at
the center of the eye, the fovea, are not parallel to the eye's horizontal
. The rotation of the image in the other eye is the
opposite.
Thus one would observe a torsional disparity
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When
Listing's plane rotates temporally by as much as the eyes
converge, horizontal lines at the center of the eye, the
fovea, stay parallel to the eye's
horizontal.
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