Vergence

A vergence is the simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision.



When a creature with binocular vision looks at an object, the eyes must rotate around a vertical axis so that the projection of the image is in the centre of the retina in both eyes. To look at an object closer by, the eyes rotate 'towards each other' (convergence), while for an object farther away they rotate 'away from each other' (divergence). Exaggerated convergence is called cross eyed viewing (focussing on the nose for example). When looking into the distance, or when 'staring into nothingness', the eyes neither converge nor diverge.

Vergence movements are closely connected to accommodation of the eye. Under normal conditions, changing the focus of the eyes to look at an object at a different distance will automatically cause vergence and accommodation.

Vergence dysfunction
A number of vergence dysfunctions exist:
 * Basic exophoria
 * Convergence insufficiency
 * Divergence excess
 * Basic esophoria
 * Convergence excess
 * Divergence insufficiency
 * Fusional vergence dysfunction
 * Vertical phorias