Rotation of Listing's plane with convergence: Independence from eye position

PURPOSE. To determine whether asymmetrical vergence results in a rotation of Listing's plane independent of vergence-associated changes of eye position in the orbit. METHODS. Six normal subjects were required to fixate on a 3 x 3 array (40°on a side) of light-emitting diodes arranged on a flat screen 124 cm from the subject. Disparity-induced vergence was elicited with a horizontal Fresnel prism (30 cm/m, ~17°) placed in front of one eye. In four subjects accommodative vergence (10°to 15°) was produced by placing a minus spherical lens in front of one eye while the other eye was covered. Eye position was measured binocularly using three-axis search coils. Control data were collected without prisms during monocular and binocular viewing. For all data a planar regression was used to fit torsional eye position as a function of horizontal and vertical position to calculate the horizontal and vertical primary positions that define the orientation of Listing's plane. RESULTS. In the prism experiment, the horizontal primary position of the eye not wearing the prism rotated temporally by 3.9°± 1.7°compared with the both eyes viewing control condition. The rotation of the prism eye was in a similar range (3.4°± 2.0°). With accommodation, the horizontal primary position of the viewing eye rotated temporally by 4.4°± 1.4°compared with the monocular viewing control. In both the accommodation and the prism paradigms there was usually a rotation of vertical primary position downward. CONCLUSIONS. Vergence-induced changes in Listing's plane can be independent of changes in orbital position associated with vergence. This finding supports a role for changes in central innervation in the elaboration of Listing's law.