Dorsal oblique

The dorsal oblique muscle is a striated muscle of the orbit, part of the muscles of the eyeball. It originates around the optic canal and runs rostrally along the dorsomedial wall of the orbit towards the trochlea. It then reflects towards the eyeball, where it inserts under the dorsal rectus muscle.

Shape: Orbital striated muscle forming an angle at the trochlea

Origin: Apex of the orbit, surrounding the optic canal

Insertion: Dorsolateral part of the equatorial region of the eyeball

Relations: Posterior and then dorsomedial to the eyeball, dorsomedial to the other bulbar muscles, attached to the trochlea

Action: Primarily intorsion, but also abduction and depression of the eye

Antagonist: Ventral oblique muscle

Vascularization: Muscular branches of external ophthalmic artery, ophthalmic plexus

Innervation: Trochlear nerve

Description:

The dorsal oblique muscle is one of the striated muscles of the orbit.

It originates at the apex of the orbit near the optic canal, attaching to the periorbita like the other muscles of the eyeball, then traveling rostrally. However, it takes a dorsomedial direction to join the trochlea, located dorso-medially to the eyeball, on the wall of the orbit. At the trochlea, it is surrounded by a vagina synovialis. It crosses the trochlea to change direction and run laterally towards the eyeball, ending in a tendon that passes between the dorsal rectus muscle and the sclera to insert dorsolaterally. As it travels, it gradually moves away from the muscular cone surrounding the optic nerve.

Contraction of this muscle mainly triggers intorsion of the eye, but it can also cause abduction and depression of the eye. The ventral oblique muscle is antagonistic.

It is vascularized by the muscular branches of the external ophthalmic artery, and drained by veins forming part of the ophthalmic plexus.

It is innervated by the trochlear nerve, a cranial nerve that is almost entirely specific to it and is named after their relationship. This nerve enters the orbit through the orbital fissure and reaches the lateral aspect of the muscle.

Variations:

In Equidae, the nerve originates near the ethmoidal foramen, and is inserted through a wide but very thin tendon ending that passes between the dorsal rectus muscle and the eyeball to attach under the lateral rectus muscle.

In bovines, it attaches in the pre-equatorial region of the eyeball under the insertion of the dorsal rectus muscle and on the dorsal part of the insertion of the retractor bulbi.

In sheep, it attaches in the pre-equatorial region of the bulb below the insertion of the dorsal rectus muscle.

In pigs, it has a strong origin, attached to a deep pit in the orbital wall. Its insertion is thin, close to the corneal limbus.

In dogs, it attaches to the sclera between the insertions of the dorsal and lateral rectus muscles, after passing under the dorsal rectus muscle.

In cats, it ends in a thin tendon that inserts dorsolaterally onto the sclera near the eyeball equator, after passing under the dorsal rectus muscle.

In rabbits, it is isolated during its trajectory from the other orbital muscles by the ophthalmic venous sinus and the deep gland of the third eyelid. It inserts below the insertion of the rectus dorsi muscle, after passing between the fibers of the levator palpebrae superioris.

In men, this muscle originates on the common tendon ring and inserts obliquely on the posterior part of the eyeball, after passing under the superior rectus muscle.