Control theory approach to accommodation and vergence.

A control theory model that treats the accommodative system and the vergence system each as negative feedback systems is investigated. The effects of accommodative vergence and vergence accommodation are included. The controllers in this model are assumed to be linear time-invariant operators. Only time-independent stimuli are considered. If vergence accommodation is neglected, the model is consistent with classical graphical analysis. By including vergence accommodation, several important changes occur. Disparity vergence is not, in general, equal to the dissociated phoria. The shape of the zone of single, clear, binocular vision is changed. Instabilities in the system arise.