Listing´s Law states that with the head stationary, upright and the eyes fixating a distant object, all rotation axes of the eye lie in the same plane. Listing’s Law is considered one of the most important principles in eye movement physiology, by which a special suspending apparatus (“Listing’s apparatus”) and a central nervous control system of the brain reduces redundant degrees of freedom for 3D eye positions (prerequisite is central fixation). Especially cyclo inward-, outward rotating components are in consequence “predefined” for a fixed target position.
This in consequence requires always the same amount of cyclo fusion for a certain eye position that supports binocular vision, especially fusion. This limitation reduces eye movements in three-dimensional space, but makes all intended eye positions confined to a constant cyclo rotation, depending on eye position.
Using end points of rotation axes (rotation vectors) to plot 3D eye positions, all positions will lie closely scattered along a plane (Listing’s Plane). SEE++ calculates these rotation vectors and subsequently visualizes Listing’s plane.
Listing’s plane therefore characterizes torsional behavior of an eye by relating rotational quantities in terms of rotation vectors to an average plane. These rotation vectors are defined as axis-angle rotations from primary position to all other available eye positions, where the direction of the vector is equal to the rotation axis and its length corresponds to the angle of rotation. When plotting the endpoints of these rotation vectors for a variety of eye positions in 3D, all these points will lie closely scattered around a plane. This plane will be fronto-parallel aligned with the X-Z axes for a healthy eye, where eye positions were measured in stationary upright head position.
Following these definitions, pathological situations in eye motility which also affect torsional behavior of eye rotations can cause modifications in the alignment of Listing’s plane with respect to its ideal X-Z orientation in “normal” healthy eyes. In accordance with clinical studies, an unilateral damage of the trochlear nerve leads to paresis of the superior oblique muscle and consequently to a vertical hyperdeviation of the affected eye.
Since the affected muscle is primarily responsible for intorsional rotation, the affected eye shows an abnormal torsional behavior as a function of vertical eye position. Thus, maximum abnormal extorsion can be found in downgaze. As a consequence of this pathological eye motility, Listing’s plane shows a significant temporal tilt due to abnormal torsional behavior, especially in downgaze. This temporal tilt can be explained as a direct consequence of the reduced force of superior oblique muscle.
Other reactions of the orientation of Listing’s plane can be found when simulating muscle palsies. In superior rectus muscle palsy, Listing’s plane significantly turns medially and slightly backward. This is due to the loss of intorsional function in abduction and the primary elevating function in adduction, resulting in pathological extorsional rotation of the affected eye.