Analysis of tonic and accommodative vergence disorders of binocular vision.

Tonic and accommodative vergence disorders of binocular vision are analyzed with separate methods. The center of symmetry and the associated phoria of forced duction fixation disparity curves are two criteria used for prismatic correction of tonic vergence disorders. The associated phoria is corrected physiologically when patients who have tonic disorders are able to develop prism adaptation with orthoptic exercises. Graphical methods are used to analyze accommodative disorders resulting from mutual interactions between accommodation and convergence. Graphic analysis illustrates that patients with high AC/A ratios have greater demands upon fusional divergence than other patients with similar ocular deviations who have normal or low AC/A ratios. Prism adaptation, which has no direct influence upon the open-loop accommodative response, replaces corrective fusional vergence innervation and thereby eliminates the main stimulus to convergence accommodation and its exaggeration of accommodative convergence. Because prism adaptation has a response time of 15 to 30 sec, abnormal accommodative convergence interactions exaggerated by convergence accommodation can be transient in patients with normal prism adaptation. Accommodative convergence disorders in patients who lack prism adaptation are classified as sustained. Orthoptic exercises which develop fast fusional vergence are recommended for the transient disorders and additional exercises to develop prism adaptation are recommended for the sustained disorders of accommodative vergence interactions.