Superior Oblique Muscle

Superior oblique muscle is one of the extra ocular muscles that control the movements of the eye. There are six extraocular muscles for each eye (four recti-superior rectus, inferior rectus, medial rectus, lateral rectus. Two oblique muscles-superior oblique muscle, inferior oblique muscle). For any muscle the salient points to be known are its origin and insertion, action of the muscle, nerve supply, blood supply, venous drainage.
Characteristics Superior Oblique Muscle

A) Origin and insertion of superior oblique muscle: The superior oblique muscle arises from the bone above and medial to the optic foramina. It runs forward and turns around a pulley –‘the trochlea’ (present in the anterior part of the superomedial angle of the orbit) and is inserted in the upper and outer part of the sclera of the eye behind the equator.

B) Actions of the superior oblique muscle: the superior oblique muscle is not parallel to the optical axis. It makes an angle of 51 degrees with the optical axis in the primary position of the eye. So it has subsidiary actions in addition to the main action. Also the action of the muscles depends on the position of the eye.

In primary position of the eye, the primary action of the superior oblique muscle is intorsion. The secondary action is depression. The tertiary action is abduction.

In an abducted eye, the superior oblique muscle can cause only intorsion of eye.

In an adducted eye, the superior oblique muscle causes only depression.

Algebra is widely used in day to day activities watch out for my forthcoming posts on Adjoint Matrix and Function Calculator. I am sure they will be helpful.

The torsions are defined in terms of the direction of movement of the upper margin of the pupil at 12 O’clock position.

C) Nerve supply: the superior oblique muscle is supplied by the IV cranial nerve or trochlear nerve.

When the trochlear nerve is damaged, diplopia occurs on looking downwards. Vision is single so long as the eyes look above the horizontal plane.

D) Blood supply: supplied through the branches arising from ophthalmic artery.

E) Venous drainage: By the superior ophthalmic vein.