What is "vergence"

1902 in ophthalmology, from verge (v.) + -ence. From 1660s as "fact or condition of being inclined" (toward something). Related: Vergency.

n. 1 (context physics English) A measure of convergence or divergence of rays 2 (context physiology English) The simultaneous turning of both eyes when focusing

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 (focusing 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, sometimes known as the accommodation-convergence reflex.

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

In structural geology, the vergence of a fold is the direction in which an antiform or synform is inclined or overturned. The term vergence comes from the German vergenz, which means "overturn".

When folds are symmetrical, the vergence tells a geologist only where to find the next antiform or synform. However, in asymmetric folds, wherein one limb of a fold is longer than the other, the vergence is dominantly in the direction in which thrusting took place.

If a number of deformation phases can be recognized in a rock, each phase may have its own vergence. However, because each succeeding phase deforms structures (and geometries) of older phases, the vergence of each of the older phases may be of little use.

Geometrically the vergence is determined with respect to the up-dip direction of the axial plane of the fold. The axial plane will physically coincide with the axial plane foliation, if folding deformation of the rock is sufficient to cause a foliation.

Vergence does not mean the direction of slip along a fault—even though it is widely misused in this way. Thus, a "southeast-vergent fault" means a fault that has been rotated toward the southeast; "southeast-directed fault" is correct word use for indicating the direction of motion along a fault.

Category:Structural geology

The vergence (typical symbol: L) of a light bundle in optics is the reciprocal of the distance between the point of focus and a reference plane. It is measured in dioptres (1 D = 1 m). Vergence can also be understood as a measure of the curvature of the optical wavefront. However, it is only fully valid in geometrical optics, not in Gaussian beam optics or in wave optics, where the wavefront at the focus is wavelength-dependent and the curvature is not proportional to the distance from the focus.

Convergence describes the situation when the light rays are approaching each other, and its values are positive. Divergence is measured as negative dioptres, and means that the beams are originating from a point.

Vergence may refer to:

• Vergence, the simultaneous movement of both eyes in opposite directions, needed for binocular vision
• Vergence (optics), the reciprocal of the distance between the point of focus and a reference plane
• Vergence (geology), a property of deformed rock