Eye movement

The Eye movements can be divided into active and passive movements. While active eye movements are used to absorb visual information, passive eye movements are used to diagnose motility disorders.

What are eye movements?

The human eye in cross section with the anatomical components. Click image to enlarge.

The entirety of all eye movements is also called Oculomotor function or Eye motility designated. The eyeballs (bulbi oculi) have various freedom of movement. The rotation of the eye is called duction. Torsions are rolling movements and versions denote gaze turns or eye movements in the same direction. The versions can in turn be divided into fast versions or slow versions. The opposite of versions are vergences. These are movements of the eyes in opposite directions.

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Eye movements happen voluntarily, involuntarily, consciously and unconsciously. The eye movement is controlled via numerous control loops. Not only the eye muscles, but also the central nervous system (CNS) or the retina are involved in these control loops.

Function & task

A total of six muscles on the eye are responsible for the movements. The lateral rectus muscle turns the eyeball to one side when it contracts. It is the only eye muscle that is innervated by the abducens nerve (6th cranial nerve).

The medial rectus muscle causes the eye to turn inward. The superior rectus muscle is responsible for the upward rotation of the eyeball. The inferior rectus muscle, on the other hand, causes the eye to lower. These three eye muscles are innervated by the oculomotor nerve. The oculomotor nerve is the 3rd cranial nerve. It also supplies the inferior obliquus muscle. This turns the eyeball upwards and can also turn the upper half of the eyeball outwards. The superior oblique muscle turns the eyeball downwards. Innervation is provided by the 4th cranial nerve, the trochlear nerve.

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The eye muscles are used to move the visual axis when tracking a visual object. Through a complicated interplay of nerves and muscles, the visual axes of both eyes are coordinated with one another and directed to a specific object. With the same eye movements, both eyeballs form a functional unit.

The combinations of abduction and adduction, depression and elevation as well as internal and external rotation enable people to see three-dimensionally. Different eye movements are possible depending on the requirements.

Similarity is characteristic of conjugated eye movements. The conjugate eye movements include saccades, eye tracking, and nystagmus. Saccades are very rapid eye movements. The point of fixation changes constantly. However, only the images are perceived at the time of fixation. The image shifts caused by the rapid eye movements are masked out. In contrast to the saccades, eye following movements are rather slow. They are used to fix an object that is moving. Nystagmus is a combination of saccades and eye movements.

With vergence movements, the angle of the visual axes changes. These eye movements are used to focus objects. Convergence movements are necessary when viewing a nearby object. If there is an object in the distance, a divergence movement occurs. All eye movements can be controlled arbitrarily or reflexively.

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However, eye movements are not only used for the visual process. Your eyes move even when you sleep. Rapid eye movements in quick succession are the hallmark of so-called REM sleep. REM stands for Rapid Eye Movement. REM phases are often dream phases. Tests in sleep laboratories indicate that the eye movements in the dream are actually carried out by the eye muscles. Usually the muscles are not very active during sleep. Why the eyes move so vigorously during the REM phases is not fully understood.

Eye movements are also used therapeutically. EMDR therapy (Eye Movement Desensitization and Reprocessing) is a psychotherapeutic method that is used to treat trauma. The basic assumption of this form of therapy is that certain eye movements are linked to memories in the brain. The eye movements are supposed to activate memory centers in the brain. A connection between the right and left hemispheres of the brain should also be provoked by EMDR therapy.

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Illnesses & ailments

Eye movement disorders are numerous. Squint is a very common condition. In medical jargon, strabismus is also known as strabismus. It is a disturbance of the balance of the eye muscles. The extent and form of strabismus can vary widely. What is common to all forms, however, is that the lines of sight deviate from one another either permanently or when an object is fixed.

Some forms are not pathological, but simply deviate slightly from the norm. Problems with vision do not arise here. However, the majority of strabismus forms are associated with serious visual impairments. Strabismus can be congenital or, for example, acquired through a stroke or an accident.

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Nystagmus (eye tremors) can occur both physiologically and pathologically. Physiologically, for example, nystagmus can be seen when looking out the window of a moving car or train. The eye tremors are pathological, for example, in dizziness, cataracts or in [[scars] on the retina.

A failure of the eye muscles occurs when the supplying nerves are paralyzed. The most common paralysis is the oculomotor nerve. This paralysis is also known as oculomotor paresis. Oculomotor paresis usually occurs as part of cerebral haemorrhage. Vascular disorders or a stroke can also lead to paresis of the cranial nerve.

With a complete oculomotor paresis, all internal and external eye muscles are affected by the paralysis. The affected eyeball points down and out. In partial oculomotor palsy, not all muscles are affected. An eye malposition is not always visible here. Rather, it leads to visual disturbances and a dilated pupil.