The totality of all eye movements is also known as oculomotor or eye motility. The eyeballs (Bulbi oculi) are free to move freely. The rotational movement of the eye is called a duction. Twists are rolling motions and versions indicate gaze or eye movements. The versions can be subdivided into fast versions or slow versions. The opposite of versions are Vergenzen. These are opposing movements of the eyes.
Eye movements happen arbitrarily, involuntarily, consciously and unconsciously. The control of the eye movement takes place via numerous control circuits. Not only the eye muscles but also the central nervous system (CNS) or the retina (retina) are involved in these regulatory circuits.
In total, six muscles on the eye are responsible for the movements. The rectus lateralis muscle turns the eyeball aside during a contraction. It is the only ocular muscle innervated by the nervus abducens (6th cranial nerve).
The Musculus rectus medialis causes an inward rotation of the eye. For the rotation of the eyeball upwards the Musculus rectus superior is responsible. On the other hand, the inferior rectus muscle causes an eye depression. These three eye muscles are innervated by the oculomotor nerve. The oculomotor nerve is the third cranial nerve. It also supplies the inferior oblique 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. The innervation takes place through the 4th cranial nerve, the trochlear nerve.
The eye muscles serve to move the visual axis in the pursuit of a visual object. Through a complex interaction of nerves and muscles, the visual axes of both eyes are matched and directed to a specific object. Through 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 allow the human three-dimensional vision. Depending on the requirements, different eye movements are possible.
Characteristic of conjugated eye movements is the sense of coherence. Conjugated eye movements include saccades, eye tracking, and nystagmus. Saccades are very fast eye movements. The fixation point changes constantly. However, only the images are perceived at the time of fixation. The image shifts caused by the rapid eye movements are hidden. Eye tracking is rather slow compared to saccades. They serve to fix an object that moves. Nystagmus is a combination of saccades and eye tracking.
Vergence movements change the angle of the visual axes. These eye movements serve to focus objects. Convergence movements are necessary when looking at a nearby object. If an object is in the distance, a divergence movement takes place. The control of all eye movements can be arbitrary or reflexive.
Eye movements, however, not only fulfill vision tasks. Even in sleep, the eyes move. Fast and short consecutive eye movements are the hallmarks 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. Normally, the muscles are only slightly active during sleep. Why the eyes move so hard during the REM phases is not fully understood yet.
Eye movements are also used therapeutically. Eye Movement Desensitization and Reprocessing (EMDR) therapy is a psychotherapeutic method 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 intended to activate memory centers in the brain. Also a connection of right and left brain half is to be provoked by the EMDR therapy.
There are numerous disorders of eye movement. A very common disease is strabismus. In medical terminology, squinting is also referred to as strabismus. It is an equilibrium disorder of the eye muscles. The extent and severity of strabismus can be very different. Common to all forms, however, is that the visual lines diverge either permanently or when fixing an object.
Some forms are not pathological but merely slightly deviate from the norm. Problems with vision do not occur here. However, a large part of the strabismus forms are accompanied by serious visual impairments. Squinting may be congenital or acquired for example from a stroke or an accident.
Nystagmus (eye shaking) can be both physiological and pathological. Physiologically, for example, a nystagmus appears when looking out the window of a moving car or train. For example, eye tremor is pathological in dizziness, cataracts, or in the retina.
A failure of the eye muscles occurs in a paralysis of the supplying nerves. Most commonly, the oculomotor nerve is affected by paralysis. This paralysis is also known as oculomotor palsy. Oculomotor palsy usually occurs in the context of cerebral hemorrhage. Vascular disorders or stroke may also result in paresis of the cranial nerve.
In complete oculomotor palsy, all internal and external eye muscles are affected by the paralysis. The affected eyeball points down and out. Partial oculomotor palsy does not affect all muscles. Here is not always an eye deformity visible. It comes rather to visual disturbances and a widening of the pupil.