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, the eyes diverge until parallel, effectively fixating the same point at infinity (or very far away).

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.

As opposed to the 500° velocity, convergence movements are far slower, say, 25°. The extraocular muscles may have two types of fiber each with its own nerve supply, hence a dual mechanism.

[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

[edit] See also

• Duction
• Extraocular muscles
• Eye movements
• Version (eye)
• Autostereogram
• Eye examination
• Orthoptist

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