Body processes

Convergence Response – Function, Task & Diseases

Convergence response

The convergence reaction is the reflex constriction of the pupils upon convergence and the inward movement of both eyes when focusing on nearby objects. Convergence impairments can cause squinting , among other things .

What is the convergence response?

Convergence is a specific type of opposing eye movement. Without a convergence response, objects could not be viewed up close. The convergence response is part of a neurophysiological process. This control circuit also includes accommodation and narrowing of the pupil ( miosis ). The complex of convergence response, accommodation and miosis is also known as the near focus triad.

Function & task

The convergence response is mediated via the third cranial nerve . In medical jargon, this is called the oculomotor nerve. Together with the trochlear nerve and the abducens nerve, it is responsible for the movements of the eyes.

The convergence reaction can be divided into two reaction steps. A contraction of the medial recti muscles is triggered via the motor core of the oculomotor nerve, the nucleus nervi oculomotorii. The musculi recti mediales are muscles of the extraocular musculature . They ensure an inward rotation of the eyeballs. This movement is also known as the convergence movement.

Miosis is also induced via the parasympathetic part of the ocolumotor nerve, more precisely via the accessory oculomotor nucleus. Miosis is a temporary narrowing of the pupil. This is triggered by a contraction of the sphincter pupillae muscle.

Parallel to the convergence reaction, a contraction of the ciliary muscles is also triggered via the parasympathetic part of the third cranial nerve. The ciliary muscles are located on the outside of the radiating body (corpus ciliare) and are responsible for near accommodation .

During the convergence reaction, the turning in of the eyes allows the two lines of sight to overlap. Without this response, an object could not be viewed up close without creating a double image.

Convergence makes three-dimensional vision possible in the first place. For this vision it is necessary that the two eyeballs are directed at the same point. Only in this way can a three-dimensional image be generated from the image perceived in the central nervous system (CNS).

Diseases & Ailments

Impairments in the convergence response can lead to hyperfunction or hypofunction. The type of convergence failure is assessed using the AC/A ratio. The AC/A quotient reflects the ratio of accommodative convergence to the accommodation achieved. The ratio averages two to three degrees of convergence movement per diopter of accommodation. The AC/A quotient can be determined using the heterophoria method and using the gradient method.

Squinting that is triggered by an excessive convergence reaction is also referred to as convergence excess. The near squinting angle is very large and the far squinting angle is very small or completely absent. As a rule, when you squint, your eyeballs point inwards. But squinting is also one of the excesses of convergence. Here the near squinting angle is less pronounced than the far squinting angle.

Overall, three forms of excess convergence can be distinguished. In non-accommodative excess convergence, squinting is purely motor-related. As a rule, there is no influence by accommodative components. Non-accommodative excess convergence can be corrected with glasses . A squint operation may be necessary. The hyperkinetic accommodation excess is triggered by accommodation. The range of accommodation is normal, but the convergence performance is too high. Thus, the AC/A quotient is also increased. The therapy is carried out through special glasses.

In the case of hypoaccommodative excess convergence, the near squint angle is greatly increased, and the range of accommodation is correspondingly significantly reduced. Due to the reduced accommodation, the body tries to see clearly in the vicinity with an overshooting convergence movement. The AC/A quotient is also increased here. The treatment of hypoaccommodative convergence excess is carried out with bifocal glasses . Under no circumstances should a squint operation be performed.

A convergence spasm is an excessive spasmodic movement of convergence. It is accompanied by strong accommodation and constricted pupils.

In the case of convergence insufficiency, the AC/A ratio is reduced. This is often due to a disturbance in the change in vergence angle. There are many causes of convergence insufficiency. Sensory-motor disorders or neurogenic lesions can be the underlying cause. The therapy is carried out with prism glasses , other special glasses or visual exercises. Squint operations can also be used. The best results are usually achieved with a combination of several measures.

There is also a lack of convergence in endocrine orbitopathy . This is also known as the Möbius sign. Endocrine orbitopathy is a disease of the orbit (eye socket). The disease is one of the autoimmune diseases and usually occurs in the context of a thyroid malfunction . Protrusion of the eyeballs is characteristic of endocrine orbitopathy. This phenomenon is also known as exophthalmos . This bulging of the eyes is also associated with a widening of the lid gap.

The triggers for endocrine orbitopathy are tissue changes behind the eyeball. Muscle, fat and connective tissue are affected by these structural and dimensional changes . Together with an enlargement of the thyroid gland and tachycardia , the exophthalmos forms the so-called Merseburg triad. This triad of symptoms is a classic sign of Graves’ disease .

Due to the swelling and infiltration behind the eye, the flexibility of the eye muscles is restricted. This causes pain when turning your gaze and restricted movement of the eyeballs. The Möbius sign is a typical symptom of endocrine orbitopathy. Other clinical signs are the Graefe sign or the Stellwag sign.

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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.