The accommodative contribution to binocular vergence eye movements.

Forced vergence fixation disparity curves were generated for both with and without an accommodative stimulus (accommodative closed and open loop conditions respectively) for fifteen asymptomatic subjects. All subjects exhibited an exophoric shift in fixation disparity for the accommodative open loop condition at the forced convergence side of the curve. No corresponding bias was found at the forced divergence side of the curve. The findings are discussed in terms of the results of previous studies and the existing models of vergence eye movements.