Vergence

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For other uses, see Vergence (disambiguation).

A vergence is the simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision.^[1]

The two eyes converge to point to the same object

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.

[edit] Vergence dysfunction

A number of vergence dysfunctions exist:^[2]^[3]

Basic exophoria
Convergence insufficiency
Divergence excess
Basic esophoria
Convergence excess
Divergence insufficiency
Fusional vergence dysfunction
Vertical phorias

[edit] References

^ Cassin B; Solomon S. Dictionary of Eye Terminology. Gainsville, Florida: Triad Publishing Company, 1990.
^ American Optometric Association. Optometric Clinical Practice Guideline: Care of the Patient with Accommodative and Vergence Dysfunction. 1998.
^ Duane A. "A new classification of the motor anomalies of the eyes based upon physiological principles, together with their symptoms, diagnosis and treatment." Ann Ophthalmol. Otolaryngol. 5:969.1869;6:94 and 247.1867.