19. The Orbit

What separates the periorbital from the orbital space?

The orbital septum.

What muscle surrounds the eye and mediates blinking?

Orbicularis oculi.

What structure lines the inner surface of the eyelids and surface of the eye?

Conjunctiva.

What gives the eyelids semi-rigidity?

Superior and inferior tarsal plates.

What muscle works with levator palpebrae superioris to elevate the eyelid?

Superior tarsal muscle (Mueller’s).

What anchors the tarsal plates to the orbital rim?

Medial and lateral palpebral ligaments.

What provides somatic sensory to the upper eyelid?

CN V1 via lacrimal, supratrochlear, and supraorbital nerves.

What provides somatic sensory to the lower eyelid?

CN V2 via infraorbital nerve.

What provides afferent corneal sensation?

CN V1 via long and short ciliary nerves.

What provides efferent motor to orbicularis oculi?

CN VII (facial nerve).

What happens with CN VII damage to the eyelid?

Inability to blink, lower lid laxity → corneal drying and excessive tearing.

What muscle causes normal blinking?

Orbicularis oculi.

What muscle elevates the upper eyelid with upward gaze?

Levator palpebrae superioris (CN III).

What happens with CN III damage to the eyelid?

Ptosis.

What muscle elevates the eyelid in sympathetic response?

Superior tarsal muscle.

What happens with sympathetic denervation to the eyelid?

Ptosis.

What gland continuously produces tears?

Lacrimal gland.

How are tears wiped across the eye?

Blinking moves them lateral to medial.

Where do tears first drain?

Into superior and inferior lacrimal puncta.

Where do tears go after the puncta?

Into the superior and inferior lacrimal canaliculi.

Where do tears go after the canaliculi?

Lacrimal sac → nasolacrimal duct → inferior nasal meatus.

What produces the oily layer of tears?

Meibomian glands (in eyelids).

What produces the watery layer of tears?

Lacrimal gland.

What are the three innervations to the lacrimal gland?

Somatic sensory (CN V1), parasympathetic (CN VII via CN V2→V1), and sympathetic (from superior cervical ganglion via CN V2→V1).

Why does blinking help squeeze the lacrimal gland?

It is wrapped around the tendon of levator palpebrae superioris.

What extraocular muscle is most superior in the orbit?

Levator palpebrae superioris.

Does levator palpebrae superioris move the eyeball?

No—it only elevates the eyelid.

Which bones contribute to the walls of the orbit?

Frontal, sphenoid, maxillary, zygomatic, palatine, ethmoid, and lacrimal bones.

What artery gives rise to all the arterial supply of the orbit?

Ophthalmic artery (branch of internal carotid).

Which arteries of the orbit can anastomose with facial arteries?

All except the ciliary arteries.

Name 5 key orbital arteries from the ophthalmic artery

Anterior ethmoidal, posterior ethmoidal, supraorbital, short ciliary, and lacrimal arteries.

Where do veins of the orbit drain posteriorly?

Cavernous sinus and pterygoid venous plexus.

Where do veins of the orbit drain anteriorly?

Angular venous system.

What are the two main ophthalmic veins?

Superior and inferior ophthalmic veins.

What structure allows nerves to pass through a venous space?

Cavernous sinus.

Which nerve lies inside the cavernous sinus near the internal carotid?

CN VI (abducens).

Which nerves lie in the lateral wall of the cavernous sinus?

CN III (oculomotor), CN IV (trochlear), CN V1 (ophthalmic), and CN V2 (maxillary).

Which cranial nerve innervates most extraocular muscles?

CN III (oculomotor).

Which nerve innervates the superior oblique muscle?

CN IV (trochlear).

Which nerve innervates the lateral rectus muscle?

CN VI (abducens).

What are the three main branches of CN V1 in the orbit?

Frontal, lacrimal, and nasociliary nerves.

Which nerves contribute to the long ciliary nerves?

Nasociliary branch of CN V1.

Which ganglion is associated with CN III in the orbit?

Ciliary ganglion.

Which nerves carry postganglionic parasympathetic fibers from the ciliary ganglion?

Short ciliary nerves.

What nerve provides somatic sensory innervation to the sclera and cornea?

Long ciliary nerves from CN V1.

What innervates the dilator pupillae muscle?

Sympathetic fibers via short ciliary nerves from CN V1.

What innervates the sphincter pupillae muscle?

Parasympathetic fibers via short ciliary nerves from CN III.

What innervates the ciliary body for aqueous/vitreous humor production?

Parasympathetic fibers via short ciliary nerves from CN III.

What innervates the ciliary muscle for lens accommodation?

Parasympathetic fibers (CN III) and sympathetic fibers (CN V1), both via short ciliary nerves.

What causes miosis (pupillary constriction) in denervation?

Sympathetic denervation or unopposed parasympathetic innervation.

What causes mydriasis (pupillary dilation) in denervation?

Parasympathetic denervation or unopposed sympathetic innervation.

Where does the optic nerve (CN II) exit the eyeball?

Posterior side of the globe through the optic canal.

Which artery enters with the optic nerve to supply the retina?

Central artery of the retina.

Where is the central vein of the retina located?

Travels with the central artery of the retina but in the opposite direction.

What does the lens focus light onto?

The fovea of the retina.

What are the three functions of the ciliary body?

Aqueous humor production, vitreous humor production, and lens accommodation.

What happens to the lens during parasympathetic stimulation?

Ciliary muscle contracts → lens thickens → near vision.

What happens to the lens during sympathetic stimulation?

Ciliary muscle relaxes → lens flattens → far vision.

Where is the choroid located?

Between the retina and sclera.

What structures perfuse and drain the retina?

Central retinal artery and vein in the choroid.

What are the three axes of eye movement?

Medial-lateral (elevation/depression), superior-inferior (abduction/adduction), visual gaze axis (intorsion/extorsion).

What is the primary action of the superior rectus?

Elevates, adducts, and intorts the eye.

What is the primary action of the inferior rectus?

Depresses, adducts, and extorts the eye.

What is the primary action of the superior oblique?

Depresses, abducts, and intorts the eye.

What is the primary action of the inferior oblique?

Elevates, abducts, and extorts the eye.

What is the only action of the medial rectus?

Adduction of the eye.

What is the only action of the lateral rectus?

Abduction of the eye.

Why is the H-test used?

To isolate and test the function of individual extraocular muscles.

What does the H-test chart show?

Eye positions to test muscles and their isolated movements.

Why are medial and lateral rectus straightforward to test?

They have only one primary action each.

When is a muscle isolated during testing?

When the visual gaze aligns with or is perpendicular to the muscle's anatomical axis.