Monocular vergence movements produced by external visual feedback

An external visual feedback procedure was used by three subjects with normal binocular vision to produce monocular lateral vergence (duction) movements. Feedback was provided by monitoring eye position with an alternating magnetic field system and by displaying the position of the monitored eye to the subject on an oscilloscope screen. Each subject was able to produce both unilateral abduction and adduction. For one subject, phorias were measured prior to several of the abduction feedback sessions, and an increase in exophoria and a decrease in the accommodative covergence/accommodation ratio was observed over the preexperimental measurement.