Superior oblique muscle
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- innervation: trochlear nerve (CN IV)
- origin: lesser wing of sphenoid bone adjacent to the annulus of Zinn
- course: tendon passes through the cartilaginous trochlea of the superior oblique located superiorly in the orbit on the nasal aspect of the frontal bone
- insertion: globe (posterosuperior quadrant)
- primary function: one of two ocular internal rotators
- secondary function: one of the two ocular depressors
- tertiary function: one of the three ocular abductors
Superior oblique arises from the lesser wing of the sphenoid bone, adjacent to the annulus of Zinn and superomedial to the origin of superior rectus 1.
Superior oblique runs anteriorly in the superomedial part of the orbit to reach the trochlea, a fibrocartilaginous pulley located just inside the superomedial orbital rim on the nasal aspect of the frontal bone 1,2. Passing through the trochlea it changes direction, passes deep to the superior rectus muscle, and inserts into the superior surface of the sclera, posterior to the midpoint of the eye 3.
Superior oblique is unique among the extraocular muscles in being supplied by the trochlear nerve.
In the neutral position, the primary action of the superior oblique is to internally rotate the eye (see figure 1) 3. However, because the apex of the orbit is placed medially in the skull, the orbital axis does not correspond with the optical axis of the eye in its neutral position. This means that the superior oblique has secondary actions of ocular depression and abduction (see figures 2 and 3).
If the eye is abducted by the lateral rectus such that the optical axis lines up with the orbital axis, the superior oblique produces internal rotation only, as it is acting roughly perpendicular to the orbital axis.
If the eye is adducted by the medial rectus, the optical axis runs roughly perpendicular to the orbital axis, and as a result is lined up with the axis of the post-trochlear part of the superior oblique muscle. Therefore, in adduction the superior oblique muscle produces ocular depression, and is solely responsible for this movement.
Thus, when the physician testing eye movements first asks the patient to follow their finger medially then inferiorly in the familiar H-shape, the superior oblique muscle (and the trochlear nerve that supplies it) are being directly tested 3.
- 1. Gray's basic anatomy. Churchill Livingstone. ISBN:1455710784. Read it at Google Books - Find it at Amazon
- 2. Netter FH. Atlas of Human Anatomy. (2018) ISBN: 9780323393225
- 3. Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. (2013) ISBN: 9781451119459
- 4. Imaging of the Head and Neck. Thieme. (2012) ISBN:3131505311. Read it at Google Books - Find it at Amazon