The superior oblique is one of a group of muscles known as extraocular muscles. These muscles work together to control eye movement. This muscle is among a class of muscles known as fusiform muscles, meaning that the muscle is shaped much like a spindle. This muscle begins in the portion of the eye socket that is closest to the nose and helps to rotate the eye internally.
The trochlear nerve, also referred to as the fourth cranial nerve, provides the nerve supply for the superior oblique. This nerve is different from other nerves in that it only supplies this one muscle. The trochlear nerve is named after the trochlea, a tendon whose name in Latin translates to "pulley."
The superior oblique is responsible for rotating the eye in such a way that the eye is able to look downward, as toward the lower portion of the face, such as the mouth. The lateral rectus, another of the extraocular muscles, assists greatly in this movement, as it is the primary muscle responsible for abduction of the eye. This muscle also helps to provide visual stability by working to prevent vision from rotating while looking in an upward or downward position.
Intorsion is caused by the superior oblique muscle. This means that this muscle rotates the eye toward the portion of the face known as the midline. This action is responsible for ensuring that vision is kept level, regardless of the position of the eye within the eye socket.
Superior oblique palsy occurs when the superior oblique muscle becomes weakened. It is possible for this condition to affect both eyes, although it is most commonly found in only one eye. Double vision often occurs with this condition. Another symptom can be the head tilting in a direction toward the shoulder in an often unconscious effort to correct distorted vision.
The most common cause of this kind of palsy is congenital, meaning that the patient is born with it. There is often no apparent reason for this, although a birth defect causing the skull to be misshapen, known as craniosynostosis, is sometimes present. Head trauma, such as a concussion, has also been known to cause this condition. Surgery is generally required in order to correct the visual disturbances caused by this form of palsy. The extent of the surgery on the eye muscle depends upon the level of visual disturbance as well as any other symptoms which may be present.