Dynamics of horizontal vergence movements: interaction with horizontal and vertical saccades and relation with monocular preferences

We studied the dynamics of pure vergence shifts and vergence shifts combined with vertical and horizontal saccades. It is known from earlier studies that horizontal saccades accelerate horizontal vergence. We wanted to obtain a more complete picture of the interactions between version and vergence. Therefore we studied pure version (horizontal and vertical), pure vergence (divergence and convergence) and combinations of both in five adult subjects with normal binocular vision and little phoria (< 5 degrees). The visual targets were LED's in isovergence arrays presented at two distances (35 and 130 cm) in a dimly lit room. Two targets were continuously lit during each trial and gaze-shifts were paced by a metronome. The two subjects with a strong monocular preference made vergence eye movements together with small horizontal saccades during pure vergence tasks. The other subjects, who did not have a strong monocular preference, made pure vergence movements (without saccades). These findings, suggest that monocular preferences influence the oculomotor strategy during vergence tasks. Vergence was facilitated by both horizontal and vertical saccades but vergence peak-velocity during horizontal saccades was higher than during vertical saccades.