Extraocular muscles · 20 of 24
What is the trochlea?
The trochlea is a small loop of cartilage attached to the frontal bone at the upper inner corner of the orbit, just behind the rim. The tendon of the superior oblique runs through it and turns almost a right angle, so the trochlea is the muscle's functional origin: the direction the tendon leaves the pulley is the direction it pulls the eye. It is the reason the fourth cranial nerve is called the trochlear nerve.
- Position
- Superomedial orbital rim, a few millimetres behind the edge
- Made of
- Fibrocartilage, with a synovial sheath around the tendon
- Serves
- The superior oblique tendon, which turns about 50 degrees through it
A pulley that changes what a muscle does
The superior oblique's belly lies at the back of the orbit like the recti, but the eye is not pulled towards the belly. The tendon turns at the trochlea and heads back and out to the top of the globe, so the effective pull comes from the front and the nose, and the muscle depresses, intorts and abducts. Without the pulley the superior oblique would simply be a weak elevator.
Brown syndrome
If the tendon cannot slide through the trochlea, the eye cannot look up when it is turned in, and the patient, usually a child, has an eye that stays down in adduction with a click sometimes felt at the pulley. This is Brown syndrome, congenital or after inflammation or surgery around the trochlea, and it looks like an inferior oblique palsy until forced duction shows the eye is stuck rather than weak. Trochleitis, inflammation of the pulley itself, is a tender lump at the upper inner orbit that causes a headache and pain on looking up.
Examine it
It is why the superior oblique's action is opposite to where its belly sits.
Ask OphthoSpace about the trochlea
AI responses are for education and may contain errors. OphthoSpace is not for primary clinical diagnosis.