Trochlea of superior oblique muscle

At a glance

English

Trochlea of superior oblique muscle

Latin (TA2)

Trochlea musculi obliqui superioris

System

Cartilage

Region

Head

Side

Paired, left and right

About the trochlea of superior oblique muscle

The trochlea is a short ring of fibrocartilage fixed to the frontal bone at the front of the roof of the orbit, close to its medial wall. It sits in a small hollow, the trochlear fovea, and is sometimes marked by a tiny bony spine. Its job is to redirect the tendon of the superior oblique muscle, one of the six muscles that move the eyeball, so that the muscle can pull from a point quite different from its origin.

The superior oblique arises at the back of the orbit, from the body of the sphenoid above and medial to the optic canal, and runs forward along the upper medial wall. Near the front its rounded tendon passes through the trochlea, inside a slippery synovial sheath that lets it slide. It then turns sharply backwards and outwards, passing under the superior rectus, and fans out to insert into the sclera on the upper, outer and rear quarter of the eyeball, behind its equator.

Because the working part of the muscle is the tendon running from the trochlea back to the globe, the pull comes from the front and inside. This is why the superior oblique depresses the eye even though it is attached to its upper surface, and why its depressing action is strongest when the eye is turned in towards the nose. It also rotates the top of the eye inwards (intorsion) and helps turn the eye outwards. Looking down and in, as when reading or walking down stairs, depends on it.

The trochlea lies just under the skin at the upper inner corner of the orbit and can be damaged by blows or by surgery in that area. Inflammation around it, trochleitis, causes local pain and tenderness that worsens when the eye looks up and in. In Brown syndrome the tendon cannot slide freely through the pulley, so the eye fails to rise when turned towards the nose. Weakness of the muscle itself, as in a fourth nerve palsy, gives vertical double vision worst on looking down.

Attachments and function

Attaches from

Fixed by fibrous tissue to the trochlear fovea or spine of the frontal bone at the upper medial corner of the orbit.

Attaches to

Encircles the tendon of superior oblique, which leaves it to insert into the posterolateral upper quadrant of the sclera.

Function

Acts as a pulley, turning the tendon of superior oblique so that the muscle depresses, intorts and abducts the eye.

Nerve supply

Lies in the territory of the supratrochlear and infratrochlear nerves; the muscle whose tendon it carries is supplied by the trochlear nerve.

Blood supply

Small branches of the ophthalmic artery, chiefly the supra-orbital and supratrochlear arteries.