The superior oblique muscle is a muscle of the external eye musculature that is one of the skeletal muscles and is motor innervated by the fourth cranial nerve. The muscle is essential for the downward gaze of the eyes and interacts harmoniously with the other muscles of the external eye musculature. Paralysis of the muscle leads to strabismus with double vision.
What is the superior oblique muscle?
From an evolutionary biology perspective, humans are referred to as eye-controlled creatures. Accordingly, evolutionary biologists advocate that humans have historically relied primarily on their visual perception to form a picture of their surroundings and to respond to the environment. Thus, eye movements have played their part in the survivability of the human species. Eye movements are a complex interplay of contractions of different muscles. The eye muscles are composed of several skeletal muscles. One of these is the superior oblique muscle, also known as the superior oblique muscle. In animals, this muscle is sometimes referred to as the obliquus dorsalis muscle or the patheticus muscle. The muscle is a skeletal muscle of the external eye musculature, which also includes the superior rectus, lateral rectus, inferior rectus, medial rectus, and inferior oblique muscles. All eye movements in humans are initiated by the external eye muscles.
Anatomy and structure
The superior obliquus muscle arises from the os sphenoidale, periorbita, and dural sheath on the optic nerve. The motor muscle pulls in a rostral direction via musculus rectus medialis. At the orbital rim, the tendon of the muscle pierces the connective tissue of the trochlea, which in the form of the hypomochlion serves to redirect the muscle traction. Continuing in a dorsal direction, the superior oblique muscle has an insertion at the temporal superior quadrant of the eyeball, where it sets dorsal to the equatorial line across the sclera. The motor innervation of the muscle is given with the trochlear nerve, which is the fourth cranial nerve. Like all other motor nerves, this nerve does not carry exclusively motor fibers, but is also equipped with sensory parts. Via the afferent sensitive parts, position and tone information from the muscle spindles and the Golgi tendon apparatus of the muscle is permanently sent to the central nervous system. As a skeletal muscle, the superior oblique muscle consists of the actual muscle fibers that provide contraction and some auxiliary tissues, such as a dermal connective tissue outer layer in the form of fascia.
Function and tasks
The main function of the superior oblique muscle is to lower or depress the eye, which is associated with inward eye rolling and slight abduction. Inward rolling is also referred to as incycloduction. In terms of adduction, the muscle is purely a depressor. Inward rolling of the eye increases with increasing outward gaze. Together with the other muscles of the external eye musculature, the superior oblique muscle is responsible for all movements of the eye. Humans have four straight and two oblique eye muscles that interact in a complex manner. The external eye muscles thus jointly perform all rotational movements of the eye in all directions through coordinated contraction. In addition, all external eye muscles together ensure that the eye positions have a stable relationship to each other. The trochlear nerve causes only the superior oblique muscle to contract. The other eye muscles of the external eye musculature receive their commands from the central nervous system via the oculomotor nerve and the abducens nerve, i.e. the third and sixth cranial nerves. At rest, that is, without actively nerve-initiated muscle contraction, the basic tone of the external eye muscles ensures that the eye does not twist.
Diseases
Failure of the trochlear nerve causes the superior oblique muscle to fail, thus affecting eye position in the resting position. Provided that all other muscles of the external eye musculature are still functional, the affected eye is rotated medially upward after the failure of the superior oblique muscle by the tone of the still functional eye muscles.Paralysis of the motor innervating trochlear nerve is also known as trochlear palsy and is clinically associated with strabismus and corresponding double vision in the sense of diplopia. The upward deviation of the affected eye is also known as hypertropia. The concomitant inward deviation of the gaze is called esotropia. The outward rolling around the sagittal axis due to paralysis again corresponds to excyclotropia. In the case of paralysis of the superior oblique muscle, double images occur, especially on the vertical axis, which are triggered in particular by downward gaze to the healthy opposite side. Often, patients with such ocular muscle paralysis tilt their head to the healthy side to compensate for the double images and functional impairment. This symptom is also known as ocular torticollis. Paralysis of the motor-supplying nerve and resulting paralysis of the superior oblique muscle result from traumatic, deficiency-related, tumor-induced, compression-related, or bacterial or autoimmunologic inflammatory damage to the nerve tissue. In the case of isolated unilateral damage to the supplying nerve, paralysis symptoms occur on exactly the opposite side of the actually affected side due to its anatomical peculiarities. Beyond paralysis, therapeutic interventions on the superior oblique muscle must take into account the proximity of its wide-ranging insertion site to the external vortex vein. The muscle’s close proximity to this vein makes vascular injury particularly likely during surgical procedures within this area.
