Body processes

Convergence – function, task and diseases

Convergence

The term convergence goes back to the Latin word “convergere” and means “to incline towards one another”. The position of the eyes , with which the lines of sight intersect directly in front of the eyes, is called convergence.

What is the convergence?

Despite farsightedness (hyperopia), young adults and children are able to see clearly by compensating for their ametropia. Technical jargon refers to this equalization as accommodation . The ciliary muscles of the eyes become tense, which increases the refractive power of the lens .

People without visual impairment do not need to adjust their visual acuity to see clearly up close. Both eyes move inward at the same time to get the correct starting position for near vision. This process is known in technical terms as convergence.

Both processes together are referred to as close-up or close-up fixation . This natural process enables humans to view objects up close without seeing double images .

Function & task

Triggering an arbitrary converging movement is often referred to as squinting , but this is not correct because the visual lines of the left and right eyes fix on nearby objects in parallel and do not differ from each other. So-called strabismus occurs only when the reflex constriction of the pupils is impaired. Both eyes then show restricted inward movements. Depending on the severity of the convergence disorder, there is varying degrees of squinting. Doctors speak of an excess of convergence.

Without convergence and convergence response, humans would not be able to see in three dimensions. Three-dimensional vision requires both eyeballs to align to the same point in order to create a three-dimensional image via the central nervous system (CNS).

The convergence response is a neurophysiological process. This control circuit also includes the narrowing of the pupils ( miosis ) and accommodation. Accommodation is an adaptation of the eyes to guarantee trouble-free close-up vision. The complex of pupillary constriction, convergence response and near focus is called the near focus triad.

The convergence response occurs via the third cranial nerve . Technical jargon refers to this as the oculomotor nerve . Together with the sixth cranial nerve ( Nervus abducens ) and the fourth cranial nerve ( Nervus trochlearis ), this is responsible for the execution of eye movements. Via the motor nucleus of the third cranial nerve, a contraction of the extraocular muscles occurstriggered. With the help of these eye muscles, the eyeballs are able to move inward. This process is called convergence movement. Contraction of the muscles around the eyes (musculus sphincter pupillae) causes a temporary constriction of the pupils. At the same time, the extraocular muscles contract to fixate on nearby objects.

The convergence response, by turning the eyes inward, allows the two lines of sight to overlap and avoids double vision. Without this process, viewing objects up close would not be possible.

Diseases & Ailments

If the convergence reaction is limited, there is underfunction or overfunction. The degree of an existing convergence disorder is determined using the AC/A quotient in squint medicine ( strabology ). It is an indicator of the pathological condition of binocular vision (binocular vision).

The doctor determines to what extent the patient is able to use the motor and sensory abilities of both eyes together. The convergence of both eyes moves at two to three degrees per diopter. The degree of convergence failure can be determined by the gradient and heterophoria method.

Squinting is triggered by an excessive convergence response called convergence excess. If a person looks into the distance, their eyes move forward in parallel. When looking up close, the eyes move inward and look slightly downward. If you look far away again, there is a divergence. The outer eye muscles (ciliary muscles) are responsible for undisturbed vergences.

If there is a lack of convergence, the eyes are unable to adjust to distances because the muscles are too weak and can no longer contract sufficiently. People can then no longer clearly see nearby objects.

The brain activates the visual center to reduce this convergence disorder by trying to optimize the quality of the perceived images through retouching and empirical values. However, this process is strenuous and clear vision is only temporarily possible. In the long run, the visual acuity decreases, the optical error can no longer be compensated. A permanent visual impairment sets in that needs to be corrected. One eye’s impulse is then turned off while the other takes over near vision.

This is how different types of squinting arise. Presbyopia sets in between the ages of 40 and 50 . A far-sighted person notices these changes quickly because they often have to adjust their near vision.

A partially accommodative squint occurs when glasses do not completely eliminate this defective vision, but only reduce the squint angle. A spasmodic convergence performance is present with a spasm that is accompanied by constriction of the pupil and increased close focus. Insufficiency is most often caused by a disturbance in the change in the angle of the eye. It can be caused by a neurogenic or sensorimotor lesion. This visual disturbance can be partially corrected with prism glasses or visual exercises. Eye surgery is also possible.

In endocrine orbitopathy there is a convergence weakness. The term “endocrine” indicates a thyroid disorder that triggers this autoimmune disease . The protrusion of the eyeballs ( exophthalmos ) with a widened lid fissure is characteristic. Triggers are tissue changes behind the eyeballs. These dimensional and structural changes affect connective , muscle and adipose tissue . The eyes become swollen due to the infiltrated tissue, while the flexibility of the muscles is reduced. Eye movement is painful and gaze rotation is restricted.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.