Vergence

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

When under non-typical visual conditions, like when looking at a stereogram, the vergence and accommodation of the eyes will not match, resulting in the viewer experiencing the vergence-accommodation conflict.

In optometry, convergence is the simultaneous inward movement of both eyes toward each other, usually in an effort to maintain single binocular vision when viewing an object.

Convergence insufficiency is a common problem with the eyes, and is the main culprit behind eyestrain, blurred vision, and headaches.

Near point of convergence (NPC) is measured by bringing an object to the nose and observing when the patient sees double, or one eye deviates out.

In ophthalmology, divergence is the simultaneous outward movement of both eyes away from each other, usually in an effort to maintain single binocular vision when viewing an object.

A divergence of the eyes in the vertical direction is physiologically seen during a head tilt, due to vestibular signaling, and when viewing a rotating visual image.

It is an active area of research to understand the reasons why many infants with hyperopia develop accommodative esotropia whereas others do not, and which is the exact influence of the vergence system in this context.