Superior oblique muscle

At a glance

English

Superior oblique muscle

Latin (TA2)

Musculus obliquus superior bulbi oculi

System

Muscle

Region

Head

Side

Paired, left and right

About the superior oblique muscle

The superior oblique is the longest and thinnest of the extraocular muscles and the only one supplied by the trochlear nerve. It is a spindle-shaped muscle lying in the upper, inner corner of the orbit, above the medial rectus. Its tendon turns round a cartilage pulley near the front of the orbit, so its working line of pull comes from in front and inside.

It arises from the body of the sphenoid bone just above and medial to the optic canal, a little above where the superior rectus begins. The belly runs forwards along the junction of the roof and medial wall, ending in a rounded tendon. This tendon passes through the trochlea, a fibrocartilage ring fixed in a small pit of the frontal bone, the trochlear fossa. It then turns backwards and outwards, passes under the superior rectus, and fans out onto the sclera on the upper, outer and back part of the globe, behind the equator, between the superior and lateral recti.

Because it pulls the back of the eye forwards and inwards, its main action is intorsion, turning the top of the eye towards the nose; it also depresses the eye and slightly abducts it. Its depressing power is greatest when the eye is turned inwards, so in the clinic it is tested by asking the patient to look down and in, even though anatomically it pulls the eye down and out. Its key role is teamwork with the recti. Because the orbit points outwards while the eye looks forwards, the inferior rectus would tilt the eye outwards as it lowers the gaze; the superior oblique cancels that tilt, as the inferior oblique does for the superior rectus, keeping the visual world level as we look up and down.

Damage to the trochlear nerve, often after a closed head injury, weakens the muscle, giving vertical and twisted double vision that is worst when looking down, as on stairs or reading; patients often tilt the head away from the affected side to compensate. In Brown syndrome a tight tendon stops the inturned eye from lifting. Operations on the tendon range from cutting or lengthening it to tucking it, and the Harada-Ito procedure shifts it to correct twisting.

Attachments, action and supply

Origin

Body of the sphenoid bone, above and medial to the optic canal.

Insertion

Sclera on the posterosuperolateral part of the eyeball behind the equator, after passing through the trochlea.

Action

Intorts the eye, depresses it (most strongly when adducted) and slightly abducts it.

Nerve supply

Trochlear nerve (cranial nerve IV).

Blood supply

Superior muscular branch of the ophthalmic artery and the supraorbital artery.