Motor and sensory responses in fusion of vertical disparities in differentconvergence places

To study motor and sensory responses in vertical fusion at different angles of horizontal vergence in normal humans. Methods: The study included 12 normal subjects. A cross (+) extending 3.4x3 .2 degrees was presented dichoptically. Vertical disparity was introduced b y changing the vertical position of the cross in front of one eye. The disp arity was incremented by 0.08 degrees every 8 s. Distance viewing was teste d with 1 degrees of convergence demand, near vision with 6-15 degrees conve rgence demand. Eye movements were recorded using three-axis search coils. Results: Vertical fusion capability was larger at near Vision than at dista nce in 9 of 12 subjects. For the entire group, total vertical fusion capabi lity (motor plus sensory response) differed between distance (mean 1.68 deg rees) and near (mean 2.39 degrees). The motor component differed significan tly between distance (mean 1.42 degrees) and near (mean 2.13 degrees). No d ifference in the sensory component was seen between distance (mean 0.26 deg rees) and near (mean 0.27 degrees). Conclusions: Vertical fusion capability increases with convergence. This in crease is mainly due to an increase of the motor response.