Extraocular Muscles and Orbital Anatomy

Comprehensive vocabulary flashcards covering extraocular muscles, orbital ligaments, innervations, actions, clinical conditions, and ophthalmic vessels.

Medial check ligament

A strong triangular ligament extending from the sheath of the medial rectus muscle that attaches to the lacrimal bone.

Lateral check ligament

A strong triangular ligament extending from the sheath of the lateral rectus muscle that attaches to the zygomatic bone.

Ligament of Lockwood

The suspensory ligament of the eye, formed by the union of the margins of the inferior rectus and inferior oblique with the medial and lateral check ligaments, slung like a hammock.

Superior tarsal muscle

The deeper smooth portion of the levator palpebrae superioris that inserts on the upper margin of the superior tarsus and elevates the upper eyelid.

Inferior tarsal muscle

An involuntary muscle extending from the fascial sheath of the inferior rectus and inferior oblique to the lower margin of the inferior tarsus that depresses the lower eyelid.

Orbitalis

An involuntary muscle bridging the inferior orbital fissure whose action is uncertain.

Common tendinous ring

Also known as the ring of Zinn, a tendinous ring attached to the middle part of the superior orbital fissure and around the optic canal from which all four recti muscles arise.

Superior rectus insertion distance

Inserted into the sclera anterior to the equator of the eyeball at an average distance of $7.7\,\text{mm}$ from the cornea.

Inferior rectus insertion distance

Inserted into the sclera anterior to the equator of the eyeball at an average distance of $6.5\,\text{mm}$ from the cornea.

Medial rectus insertion distance

Inserted into the sclera anterior to the equator of the eyeball at an average distance of $5.5\,\text{mm}$ from the cornea.

Lateral rectus insertion distance

Inserted into the sclera anterior to the equator of the eyeball at an average distance of $6.9\,\text{mm}$ from the cornea.

Superior oblique origin

Arises from the undersurface of the lesser wing of the sphenoid, superomedial to the optic canal.

Trochlea

A fibrocartilaginous pulley attached to the trochlear fossa of the frontal bone through which the tendon of the superior oblique muscle passes.

Inferior oblique origin

Arises from the orbital surface of the maxilla lateral to the lacrimal groove near the anterior margin of the orbit.

Levator palpebrae superioris origin

Arises from the orbital surface of the lesser wing of the sphenoid bone, anterosuperior to the optic canal and the origin of the superior rectus.

Superior lamella of levator palpebrae superioris

The voluntary portion of the levator tendon inserted into the anterior surface of the superior tarsus and the skin of the upper eyelid.

Inferior lamella of levator palpebrae superioris

The smooth, involuntary portion of the levator tendon inserted into the upper margin of the superior tarsus and superior conjunctival fornix.

Trochlear nerve (CN IV)

The cranial nerve supplying the superior oblique muscle ($SO_4$).

Abducent nerve (CN VI)

The cranial nerve supplying the lateral rectus muscle ($LR_6$).

Oculomotor nerve (CN III)

The cranial nerve supplying the superior rectus, inferior rectus, medial rectus, inferior oblique, and part of the levator palpebrae superioris.

Eyeball elevation angle

Upward rotation of the eyeball around a transverse axis through an angle of $33^\circ$.

Eyeball depression angle

Downward rotation of the eyeball around a transverse axis through an angle of $33^\circ$.

Eyeball adduction angle

Medial rotation of the eyeball around a vertical axis through an angle of $50^\circ$.

Eyeball abduction angle

Lateral rotation of the eyeball around a vertical axis through an angle of $50^\circ$.

Eyeball torsions

Rotatory movements around an anteroposterior axis defined by the direction of movement of the upper margin of the pupil at the 12 o'clock position.

Superior oblique actions

Produces depression, abduction, and intorsion of the eyeball in the primary position.

Inferior oblique actions

Produces elevation, abduction, and extorsion of the eyeball in the primary position.

Inferior rectus actions

Produces depression, adduction, and extorsion of the eyeball in the primary position.

Superior rectus actions

Produces elevation, adduction, and intorsion of the eyeball in the primary position.

Medial rectus action

Produces only adduction of the eyeball.

Lateral rectus action

Produces only abduction of the eyeball.

Conjugate ocular movements

Harmoniously coordinated movements of both eyes acting together in various combinations.

Concomitant squint

A congenital condition caused by muscle weakness or paralysis where there is no limitation of movement and no diplopia.

Paralytic squint

A condition caused by extraocular muscle paralysis characterized by limited movements, diplopia, vertigo, head turn toward the paralyzed muscle's function, and false orientation of the visual field.

Nystagmus

Involuntary, rhythmical oscillatory movements of the eyes resulting from incoordination of the ocular muscles.

Ophthalmic artery

A branch of the internal carotid artery originating anterior to the anterior clinoid process that enters the orbit through the optic canal inferolateral to the optic nerve.