(17) Orbit & Ear

orbit

cone-shaped space that houses the eyeball. projects into the face, with a deep apex.

Bones of the orbit

Frontal, zygomatic, sphenoid, ethmoid, lacrimal, maxillae

Bony features of the orbit

-fossa for lacrimal gland

-superior orbital fissure

-inferior orbital fissure

-infraorbital groove

-infraorbital foramen

-optic canal

-lacrimal groove

-nasolacrimal canal

fibrous tunic of eye

composed of the sclera and cornea. transparent so that light can enter.

Sclera

white part of the eye that serves as a protective outer covering

Cornea

The clear tissue that covers the iris & pupil, serving as a protective outer covering.

corneoscleral junction

Meeting point of cornea and sclera.

iris

a ring of smooth muscle tissue anterior to the lens that forms the colored portion of the eye around the pupil and controls the size of the pupil opening.

pupil

the adjustable opening in the center of the eye through which light enters

lacrimal caruncle

bump in the medial angle of the external eye

medial angle/canthus of eye

where two eyelids meet medially

lateral angle/canthus of eye

where two eyelids meet laterally

lens of eye

the part of the eye that refracts light

aqueous humor

the clear fluid filling the space in the front of the eyeball between the lens and the cornea. helps maintain shape of eyeball.

vitreous humor

the clear jellylike liquid filling the eyeball behind the lens. helps maintain shape of eyeball.

ciliary body

Structure surrounding the lens that connects the choroid and iris. It contains ciliary muscles, which control the shape of the lens.

zonular fibers

extensions of the ciliary body that attache to the lens & hold it in place

choroid

thin layer of CT that contains the blood vessels of the eye

Retina

the light-sensitive inner surface of the eye

fovea centralis

the part of the retina with the greatest visual acuity, onto which the lens focuses light

optic disc

Region at the back of the eye where the optic nerve & vessels meet the retina. It a natural blindspot.

Optic Nerve (CN II)

the nerve that carries neural impulses from the retina of the eye to the brain

periorbita

periosteum of the bones of the orbit. continuous with skull & with orbital septa.

superior orbital septum

Fibrous membrane at the top of the orbit that is continuous with periorbita. Attaches to the superior tarsal plate.

superior tarsal plate

connective tissue structure within the upper eyelid that is attached to the superior orbital septum. allows upper eyelid to be folded back. contains tarsal glands.

tarsal glands (meibomian glands)

glands in the superior tarsal plate that secrete an oily substance to prevent eyelids from sticking together & keep lacrimal fluid in.

inferior orbital septum

Fibrous membrane at the bottom of the orbit that is continuous with periorbita

inferior tarsal plate

connective tissue structure within the lower eyelid that is attached to the inferior orbital septum. allows lower eyelid to be folded back.

palpebral fissure

space between the eyelids

cilia

eyelashes

ciliary glands

modified sweat glands located between the eyelashes. infection results in a stye.

conjunctiva

transparent mucous membrane that lines the eyelids and outer surface of the eyeball. with tears, lubricates the eye & helps prevent infection. 2 regions: bulbar & palpebral.

bulbar conjunctiva

The part of the conjunctiva that lines the anterior surface of the eyeball

palpebral conjunctiva

The part of the conjunctiva that lines the underside of the eyelids

conjunctival sac

space between palpebral and bulbar conjunctiva. sealed off when the eye is closed.

superior conjunctival fornix

superior junction between palpebral and orbital conjunctiva

Inferior conjunctival fornix

inferior junction between palpebral and orbital conjunctiva

Lateral palpebral ligament

connects superior and inferior tarsi to lateral margin of orbit

Medial palpebral ligament

connects superior and inferior tarsi to medial margin of orbit

fibrous skeleton of the eyelid

-superior orbital septum

-tendon of levator palpebrae superioris

-superior tarsal plate

-lateral palpebral ligament

-inferior tarsal plate

-inferior orbital septum

-medial palpebral ligament

lacrimal apparatus

the structures that secrete and drain tears from the eye. consists of the lacrimal gland, lacrimal puncta, lacrimal canaliculi, lacrimal sac, and nasolacrimal duct.

lacrimal gland

secretes lacrimal fluid (tears)

lacrimal puncta

Small openings in the medial part of the eyelid for tear drainage.

lacrimal canaliculi

the ducts at the inner corner of each eye that collect tears and drain them into the lacrimal sac

lacrimal sac

structure that collects tears from the lacrimal canaliculi before emptying into the nasolacrimal duct

Nasolacrimal duct

empties lacrimal fluid into the nasal cavity

muscles of the upper eyelid

Levator Palpebrae Superioris & Superior Tarsal Muscle. Function to raise the upper eyelid.

levator palpebrae superioris

muscle that functions to voluntarily elevate the upper eyelid

-inserts into subcutaneous tissue of the upper eyelid & superior tarsal plate.

-Innervated by the occulomotor nerve

superior tarsal muscle

smooth muscle at the inferodistal slip of levator palpebrae superioris that involuntarily raises upper eyelid following sympathetic stimulation

-Preganglionic fibers originate in IML of T1 and synapse in superior cervical ganglion

-Postganglionic fibers follow blood vessels

Extrinsic/extraocular muscles

Lateral Rectus, Medial Rectus, Superior Rectus, Inferior Rectus,

Inferior Oblique, Superior Oblique. Function to change the orientation of the eye within the orbit.

apex of the orbit is the site of origination for

all extraocular muscles besides the inferior oblique

common tendinous ring

origin of the four rectus muscles of the eye. the ophthalmic artery also passes through.

movement of the eyes around the mediolateral axis results in

elevation or depression

movement of the eyes around the superoinferior axis results in

adduction or abduction

eye adduction

movement of the eye towards the nose (medially)

eye abduction

Movement of the eye away from the nose (laterally)

movement of the eyes around the anteroposterior/optic axis results in

internal rotation/incycloduction or external rotation/excycloduction. allows one to continue to view the world upright through an 8 degree head tilt.

Incycloduction/Internal rotation

clockwise movement of the eye

Excycloduction/External rotation

counterclockwise movement of the eye

medial rectus

Muscle that adducts the eye.

-Innervated by the oculomotor nerve

lateral rectus

Muscle that abducts the eye.

-Innervated by the abducens nerve

Cyclovertical Muscles

superior rectus, inferior rectus, superior oblique, inferior oblique. function in elevation-depression and incycloduction-excycloduction of the eye.

superior rectus

Muscle that inserts on the superior surface of the eyeball. It pulls both posteriorly & medially; functions in elevation (posterior pull) & incycloduction (medial pull)

-Innervated by the oculomotor nerve

inferior rectus

Muscle that inserts on the inferior surface of the eyeball. It pulls both posteriorly & medially; functions in depression (posterior pull) & excycloduction (medial pull)

-Innervated by the oculomotor nerve

superior oblique

Muscle that originates at the apex of the orbit & inserts on the superior surface of the eyeball, where it runs through the fibrocartilaginous trochlea. It pulls both anteriorly & medially; functions in depression (anterior pull) & incycloduction (medial pull)

-Innervated by the trochlear nerve

inferior oblique

Muscle that originates at the apex of the orbit & inserts on the inferior surface of the eyeball. It pulls both anteriorly & medially; functions in elevation (anterior pull) & excycloduction (medial pull)

-Innervated by the oculomotor nerve

incycloductors insert on the

superior surface of the eye

excycloductors insert on the

inferior surface of the eye

when the eye is abducted

the superior and inferior recti are the primary vertical movers & can do longer act as cycloductors. Superior rectus produces pure elevation & inferior rectus produces pure depression.

when the eye is adducted

the superior and inferior obliques are the primary vertical movers & can no longer act as cycloductors. Superior oblique produces pure depression & inferior oblique produces pure elevation.

if both superior rectus & inferior oblique (both elevators) are activated

their opposing cycloductive effects will cancel out & only elevation will result

if both inferior rectus & superior oblique (both depressors) are activated

their opposing cycloductive effects will cancel out & only depression will result

bulging eyes result from use of

superior & anterior obliques

Ophthalmic nerve (CNV1)

branch of CN V that carries somatic sensory fibers. splits into frontal, lacrimal, & nasociliary nerves.

frontal nerve

large middle branch of the ophthalmic nerve that splits into supraorbital and supratrochlear nerves

Supraorbital nerve

lateral branch of the frontal nerve

Supratrochlear nerve

medial branch of the frontal nerve

lacrimal nerve

lateral branch of the ophthalmic nerve that runs towards the lacrimal gland. provides somatic sensation to the conjunctiva & upper eyelid.

Nasociliary nerve

medial branch of the ophthalmic nerve that runs towards the nose. branches into the posterior ethmoidal nerve, anterior ethmoidal nerve, short ciliary nerves, and long ciliary nerves.

posterior ethmoidal nerve

lower medial branch of the nasociliary nerve that runs toward the ethmoid

anterior ethmoidal nerve

higher medial branch of the nasociliary nerve that runs toward the ethmoid

Long ciliary nerves

middle branches of the nasociliary nerve that have postganglionic sympathetics to dilator pupillae

Short ciliary nerves

lateral ranches of the nasociliary nerve that have postganglionic parasympathetics to the ciliary muscle & sphincter pupillae

ciliary ganglion

one of the terminal ganglia of the parasympathetic system, located in the posterior orbit

the trochlear nerve passes through the

superior orbital fissure to get to the superior oblique

the optic nerve passes through the

optic canal

the abducens nerve passes through the

superior orbital fissure to get to the medial/deep surface of the lateral rectus

preganglionic parasympathetics for the lacrimal gland originate

in the facial nerve

pterygopalatine ganglion

A cluster of postganglionic parasympathetic cell bodies suspended from the maxillary nerve.

postganglionic parasympathetics for the lacrimal gland

hitchhike on branches of V1 & V2 before reaching the lacrimal gland, where they initiate secretion

intraocular muscles

sphincter pupillae, dilator pupillae, ciliary muscle. All smooth muscles that function to change the shape of the lens and size of the pupil

Sphincter pupillae

circularly-arranged muscle of the iris that functions to decrease pupil diameter, & thus decrease the amount of light reaching the retina.

-Parasympathetic innervation, with preganglionic axons originating in the oculomotor nerve & synapsing in ciliary ganglion, & postganglionic axons running with short ciliary nerves

Dilator pupillae

radially-arranged muscle of the iris that functions to increase pupil diameter, & thus increase the amount of light reaching the retina.

-Sympathetic innervation, with preganglionic axons originating in T1 IML & synapsing in the superior cervical ganglion, & postganglionic axons hitchhiking on long ciliary nerves

Ciliary Muscle

smooth muscle that changes the shape of lens, which is critical for focusing vision. Functions by reducing tension on zonular fibers that suspend lens in the eye, allowing the lens to

rebound to more rounded shape.

-Parasympathetic innervation, with preganglionic axons originating in the oculomotor nerve & synapsing in ciliary ganglion, & postganglionic axons running with short ciliary nerves

the farther an object is from the eye

the less round the lens needs to be to focus light on the fovea centralis. Distance vision therefore requires little to no ciliary muscle contraction.

the nearer an object is to the eye

the more round the lens needs to be to focus light on the fovea centralis. Near vision therefore requires sustained ciliary muscle contraction.

Horner's Syndrome

Condition that occurs when the sympathetic chain at or above T2 level or its branches to head are damaged or impinged upon. 4 main symptoms:

1. Mild drooping of eyelid (ptosis)

2. Constriction of the pupil (miosis)

3. Loss of cutaneous vasodilation in response to heat or emotion

4. Loss of sweating (anhidrosis) in response to heat

*When a muscle loses innervation, it loses resting tone. So, losing dilator pupillae causes pupil to constrict at resting tone

ophthalmic artery

branch of the internal carotid artery that enters the orbit through the optic canal inferior to the optic nerve to supply blood to the eye. Branches include the lacrimal artery, central artery of the retina, supraorbital artery, supratrochlear artery, & anterior & posterior ethmoidal arteries.

lacrimal artery

lateral branch of ophthalmic artery that supplies the lacrimal gland

central artery of the retina

branch of ophthalmic artery that serves as the only direct blood supply to the retina (therefore, no artery = no vision)