Fixation disparity refers to the difference in the position of the two eyes' fixations during binocular viewing. Some synonyms for fixation disparity include binocular vision dysfunction, ocular motor imbalance, and vergence dysfunction. Binocular vision dysfunction implies that there is a problem with how the two eyes work together, while ocular motor imbalance suggests an issue with the eye muscles. Vergence dysfunction specifically refers to a disruption in the coordination of the movements made by the eyes. Other related terms include heterophoria, which is an imbalance in the resting position of the eyes, and convergence insufficiency, which is a difficulty in turning the eyes inward to focus on near objects.