Rotation of Listing's plane by horizontal, vertical and oblique prism-induced vergence.

We examined the changes in Listing's plane resulting from prismatically induced vergence. The three-dimensional angular positions of the two eyes were compared in normal subjects wearing search coils and gazing at targets 1.9 m away with and without prisms. For horizontal base-out prisms each degree of convergence in one eye yielded 0.72 deg of temporal rotation of Listing's plane in that eye. The results from vertical prisms were not what was expected from the horizontal results. A base-up prism on the right eye induced a downward and temporal rotation of Listing's plane. A base-down prism on the right eye induced an upward and nasal rotation of Listing's plane. The effects of oblique prisms were those expected from combining the effects of horizontal and vertical prisms. Thus in addition to producing a horizontal or vertical misalignment of the gaze line, prisms induce an unexpected position-dependent torsional disparity.