The superior oblique is a fusiform muscle belonging to the extra-ocular group of muscles. It originates near the nose, and is shaped like a spindle. Along with the other extra-ocular muscles, it performs the role of controlling eye movements. Its primary, secondary, and tertiary actions are internal rotation, depression, and abduction respectively. When the eye is in an abducted mode, the muscle performs the depressing action with maximum effectiveness. The fourth cranial nerve innervates only this muscle among the entire group of extra-ocular muscles. It forms a 51-degree angle with the optical axis in combination with the group of inferior oblique muscles. It supports eye rotation function in a manner that allows the eye to depress downwards. This movement receives support from another extra-ocular muscle known as the lateral rectus. Another key role of the superior oblique muscle is to provide visual stability. It resists the eye's tendency to rotate itself involuntarily when looking downwards or upwards. It also causes intorsion, which maintains the position of the eye towards the midline of the face.
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In Depth: Superior oblique