A vergence is the simultaneous movement of both eyes in opposite directions to obtain or maintain a single binocular vision.
When creatures with binocular vision see the object, the eye must rotate around the horizontal axis so that the projection of the image is at the center of the retina in both eyes. To see objects closer, the eyes rotate toward each other (convergence), while for further objects they rotate away from each other (divergence). Excess convergence is called crosseded view (focus on the nose for example). When looking into the distance, the eye diverges to parallel, effectively fixing the same point in infinity (or very far).
The vergen movement is closely related to the accommodation of the eye. Under normal circumstances, changing the focus of the eye to see objects at different distances will automatically lead to vergence and accommodation, sometimes known as the convergence-convergence convergence.
Unlike the saccade movement speed of 500 Â °/s, the vergence movement is much slower, around 25 Â °/s. The extraocular muscle may have two types of fiber each with its own neural supply, then a double mechanism.
Video Vergence
Jenis
The following types of vergence are considered to act in superposition:
- Strong vergic : vergence due to normal extraocular muscle tone, no accommodation and no stimulus for binocular fusion. Tonic vergence is thought to move the eye from an anatomical rest position (which would be the eye position if not conserved) to a physiological position of rest.
- Accommodative verification : blur-driven vergence.
- Verger Fusional (also: vergence difference , disparity-driven vergence , or refllex vergence ): vergence induced by a stimulus for binocular fusion.
- Verger proximal : vergence due to awareness of near or distant fixation objects in the absence of disparity and gestures for accommodation. This includes also the vergence caused by the subject's intention to fix the object in the dark.
Acommotative vergence is measured as the ratio between how much convergence occurs for a particular accommodation (AC/A ratio, CA/C ratio).
The proximal truth is sometimes also called voluntary vergence, which however is more commonly means that vergence is under voluntary control and is sometimes regarded as the fifth type of vergence. Voluntary verification is also required to view autostereograms as well as for voluntary eye crossings. Voluntary convergence is usually accompanied by accommodation and miosis (pupil narrowing); But often, with an extended practice, individuals can learn to separate accommodation and vergence.
Vergence is also denoted according to its direction: horizontal vergence, vertical vergence, and vergence torque (cyclovergence). The horizontal vergeritas is further differentiated into convergence (also: positive vergence) or divergence (also: negative vergence). The Vergen eye movement results from the activity of six extraocular muscles. It is preserved from three cranial nerves: nerve abducens, troklear nerves and oculomotor nerves. Horizontal verger involves mainly the medial and lateral rectus.
Convergence
In ophthalmology, convergence is the simultaneous inward movement of the two eyes against each other, usually in an attempt to maintain a single binocular vision when viewing an object. This is the only non-conjugated eye movement, but instead adds an eye. Convergence is one of three eye processes to focus the image on the retina correctly. In each eye, the visual axis will lead to the desired object to focus on the fovea. This action is mediated by the medial rectus muscle, which is innervated by the cranial nerve III. This is a type of vergence eye movement and is performed by extrinsic muscles. Diplopia, usually referred to as double vision, can occur if one of the extrinsic muscles of the eye is weaker than the other. This results because the object seen is projected onto various parts of the retina of the eye, causing the brain to see two images.
Convergence insufficiency is a common problem with the eye, and is a major cause behind eye fatigue, blurred vision, and headaches. This problem is most commonly found in children.
Convergence Point (NPC) is measured by bringing the object to the nose and observing when the patient sees twice as much, or one eye deviates outward. Normal NPC value up to 10 cm. Any NPC value that is more than 10 cm away, and usually due to high ekpofora in close proximity.
In addition, recent research also proves that the tungsten spectrum energy affects convergence that can also show impact on reading and close visual tasks due to its brightness and miosis. Prolonged reading and working under this illumination can lead to interference in convergence and visual fatigue
Divergence
In ophthalmology, divergence is the simultaneous exit movement of the two eyes of one another, usually in an attempt to maintain a single binocular vision when viewing objects. This is a type of vergence eye movement.
Maps Vergence
vergen dysfunction
A number of vergence dysfunctions exist:
- Basic ecofora
- Convergence insufficiency
- Convergence micropsia
- Excess irregularities
- Basic Esofora
- Convergent excess
- Divergence insufficiency
- Fusional vergence dysfunction (reducing fusional positive and negative verusif, with normal or nearly normal foria)
- Heterophoria
As a further type of dysfunction there is evidence for an association between vergency abnormalities in which there is an inverted foveal projection crossover such that the foveal convergence stimulus is run as a divergence movement (in place of the convergence movement) and the occurrence of schizophrenia. In this case both conditions receive treatment with non-neuroleptic methods.
The vergen control, and over-convergence associated with additional accommodation required to overcome hyperopic refractive errors, plays a role in the onset of esotropic accommodative. The classical explanation for accommodative esotropic onset is the compensation of farsightedness by way of excessive accommodative convergence. It is an active field of research to understand the reasons why many infants with hyperopia develop accommodative esotropia while others do not, and which is a definite influence of the vergence system in this context.
See also
- Cyclovergence
- Duction
- Version (eye)
- Autostereogram
- Eye check
- Orthoptist
References
Source of the article : Wikipedia
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