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Orbit, Orbital Region,
and Eyeball
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The orbits
• The orbits are bony cavities in the facial skeleton that
resemble hollow quadrangular pyramids with their
bases directed anterolaterally and their apices,
posteromedially
The orbits…
• The orbits contain and protect the eyeballs
(globes of eyes) and accessory visual
structures, which include the Eyelids,
Extraocular muscles, Nerves and vessels in
transit to the eyeballs and muscles.
• Mucous membrane (conjunctiva) lining the
eyelids and anterior aspect of the eyeballs and
most of the lacrimal apparatus, which
lubricates it
The Eyeball
• The eyeball contains the optical apparatus of
the visual system and occupies most of the
anterior portion of the orbit.
• The eyeball proper has three layers:
• Fibrous layer (outer coat), consisting of the
sclera and cornea.
• Vascular layer (middle coat), consisting of the
choroid, ciliary body, and iris.
• Inner layer (inner coat), consisting of the
retina that has both optic and non-visual parts.
Two involuntary muscles of the iris control the size of the
pupil: the parasympathetically stimulated sphincter pupillae
closes the pupil, and the sympathetically stimulated dilator
pupillae opens it
Parasympathetic fibres from the oculomotor nerve
supply sphincter pupillae and the ciliary muscle via the
ciliary ganglion, and from the facial nerve innervate the
lacrimal gland.
Sympathetic fibres supply dilator pupillae
NOTE: only the parasympathetic fibres synapse in the
ganglion.
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Arteries of the Orbit
• The blood supply of the orbit is mainly from the
ophthalmic artery, a branch of the internal
carotid artery; the infraorbital artery, from the
external carotid artery
• The central artery of the retina, a branch of the
ophthalmic artery arising inferior to the optic nerve,
runs within the dural sheath of the optic nerve until it
approaches the eyeball
• The central artery pierces the optic nerve and runs
within it, emerging at the optic disc
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Veins of the Orbit
• Venous drainage of the orbit is through the
superior and inferior ophthalmic veins, which
pass through the superior orbital fissure and
enter the cavernous sinus
• The scleral venous sinus is a vascular structure
encircling the anterior chamber of the eyeball through
which the aqueous humor is returned to the blood
circulation.
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Applied Anatomy:
Glaucoma
When drainage of aqueous humor through the
scleral venous sinus into the blood circulation
decreases significantly, pressure builds up in the
anterior and posterior chambers of the eye, a
condition called glaucoma. Blindness can result
from compression of the inner layer of the eyeball
(retina) and the retinal arteries if aqueous humor
production is not reduced to maintain normal
intraocular pressure
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Extraocular Muscles of the Orbit
The extraocular muscles of the orbit are the levator
palpebrae superioris, four recti (superior, inferior,
medial, and lateral), and two obliques (superior and
inferior).
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Extraocular Muscles of the Orbit…
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Axes of movements:
Elevation
Transverse axis
Depression
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Axes of movements:
Adduction
Abduction
Vertical axis
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Axes of movements:
Extorsion
Intorsion
Medial movement of the
superior pole of the
eyeball is intorsion;
L
lateral movement of the
superior pole is extorsion.
M
Antero-posterior axis
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Common tendinous ring
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Oblique muscles:
Superior oblique:
It arises from the undersurface of the lesser wing above
and medial to the common tendinous ring
The tendon of the muscle passes through a fibrocartilaginous pulley and is inserted into the sclera behind
the equator in postero-superior quadrant of the eyeball
Abducts, depresses, and medially rotates eyeball
Inervated by Trochlear nerve (CN IV)
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Inferior oblique:
It arises from the orbital surface of maxilla in
the floor of the orbit
Inserted into the sclera behind the equator in
the postero-superior quadrant of the eyeball
Abducts, elevates, and laterally rotates eyeball
Inervated by Oculomotor nerve (CN III)
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Superior rectus
• It arise from a common tendinous ring
• It attaches at the sclera just posterior to
corneoscleral junction
• Its function is to elevates, adducts, and rotates
eyeball medially
• Its inervetion is by Oculomotor nerve (CN III)
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Inferior rectus
• It arise from a common tendinous ring and
attaches at the sclera just posterior to
corneoscleral junction
• Its function is to depresses, adducts, and rotates
eyeball medially
• Its inervetion is by Oculomotor nerve (CN III)
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Medial rectus
• It arise from a common tendinous ring and
attaches at the sclera just posterior to
corneoscleral junction
• Its function is to Adducts eyeball
• Its inervetion is by Oculomotor nerve (CN III)
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Lateral rectus
• It arise from a common tendinous ring and
attaches at the sclera just posterior to
corneoscleral junction
• Its function is to Abducts eyeball
• Its inervetion is by Abducent nerve (CN VI)
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Levator palpebrae superioris
• It arises from lesser wing of sphenoid bone,
superior and anterior to optic canal and
attaches to the Superior tarsus and skin of
superior eyelid
• It is innervated by oculomotor nerve; deep
layer (superior tarsal muscle) is supplied by
sympathetic fibers
• Its function is to elevates superior eyelid
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Summary of the Nerve supply:
Lateral rectus - Abducent nerve (CN 6)
Medial rectus - Oculomotor nerve (CN3)
Superior rectus - Oculomotor nerve (CN3)
Inferior rectus - Oculomoter nerve (CN3)
Inferior oblique - Oculomotor nerve (CN3)
Superior oblique - Trochlear nerve (CN4)
S O4; L R6
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Action of individual muscles:
LATERAL
Inferior
oblique
A
B
D Extorsion
U
C Lateral
T rectus
I Intorsion
O
superior
N
oblique
Elevation
Depression
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MEDIAL
Superior
rectus
A
D
Intorsion D
U
Medial C
rectus T
Extorsion I
O
Inferior
N
rectus
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Lateral and Medial Recti
• Lateral Rectus
– Basic function is to ABDUCT the eye
– Innervated by cranial nerve VI, the abducens nerve
• Medial Rectus
– Basic function is to ADDUCT the eye
– Innervated by cranial nerve III, the oculomotor nerve
• Superior Rectus
– Basic function is to ELEVATE the eye
– Tested by asking the patient to look up while the eye is abducted
– Innervated by cranial nerve III
• Inferior oblique
– Basic functions are EXTORSION and ELEVATION of the eye
– Tested by asking the patient to look up while the eye is adducted
– Innervated by cranial nerve III
• Inferior Rectus
– Basic function is to DEPRESS the eye
– Tested by asking the patient to look down while the eye is abducted
– Innervated by cranial nerve III
• Superior Oblique
– Basic functions are INTORSION and DEPRESSION of the eye
– Tested by asking the patient to look down while the eye is adducted
– Innervated by cranial nerve IV, the trochlear nerve
Eye movements produced by muscles:
No movement is done by a single muscle, while some
muscle acts as a prime movers and other acts as synergists
MOVEMENT
MUSCLE
Adduction
Medial rectus, assisted by superior and
inferior recti
Abduction
Lateral rectus, assisted by the superior and
inferior oblique muscles
Elevation
Superior rectus and inferior oblique
muscles
Depression
Inferior rectus and superior oblique
muscles
Intorsion
Superior rectus and inferior oblique
Extorsion
Inferior rectus and inferior oblique
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Lacrimal Apparatus
• The lacrimal apparatus consists of the:
• Lacrimal glands: secrete lacrimal fluid, a
watery physiological saline containing the
bacteriocidal enzyme lysozyme. The fluid
moistens and lubricates the surfaces of the
conjunctiva and cornea and provides some
nutrients and dissolved oxygen to the
cornea; when produced in excess, it
constitutes tears.
• Lacrimal ducts: convey lacrimal fluid from
the lacrimal glands to the conjunctival sac.
Lacrimal Apparatus…
Lacrimal canaliculi
• Lacrimal canaliculi: commence at a lacrimal
punctum (opening) on the lacrimal papilla
near the medial angle of the eye and drain
lacrimal fluid from the lacrimal lake (L. lacus
lacrimalis; a triangular space at the medial
angle of the eye where the tears collect) to
the lacrimal sac (the dilated superior part of
the nasolacrimal duct).
• Nasolacrimal duct: conveys the lacrimal
fluid to the inferior nasal meatus.
Lacrimal fluid
• Production of lacrimal fluid is stimulated by
parasympathetic impulses from CN VII.
• When the cornea becomes dry, the eye blinks.
The eyelids come together in a lateral to medial
sequence pushing a film of fluid medially over
the cornea, somewhat like windshield wipers
when washing the car windshield
• In addition to cleansing particles and irritants
from the conjunctival sac, lacrimal fluid provides
the cornea with nutrients and oxygen.
Applied Anatomy:
a. Weakness or paralysis of a muscle causes
squint/strabismus. In this condition the two
eyes appear to look in different directions
b. Nystagmus is characterised by involuntary
oscillatory movements of the eyes. This in
due to incordination of the ocular muscles
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Ear
• The ear consists of external, middle, and internal
parts. The external and middle parts are mainly
concerned with the transference of sound to the
internal ear, which contains the organ for
equilibrium (the condition of being evenly
balanced) as well as for hearing.
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Applied anatomy –
Acute Otitis Externa
• Otitis externa is an inflammation of the external
acoustic meatus. The infection often develops in
swimmers who do not dry their meatus after swimming
and/or use ear drops, but it may also be the result of a
bacterial infection of the skin lining the meatus.
• The affected individual complains of itching and pain in
the external ear. Pulling the auricle or applying pressure
on the tragus increases the pain.
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NASAL CAVITY
Nasal Cavity
• The nasal cavity is entered
anteriorly through the
nares. It opens posteriorly
into the nasopharynx
through the choanae.
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Vasculature and Innervation of the
Nose
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Innervation of nasal cavity
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Applied anaomy- Rhinitis
• The nasal mucosa becomes swollen and inflamed
(rhinitis) during severe upper respiratory infections
and allergic reactions (e.g., hayfever). Swelling of the
mucosa occurs readily because of its vascularity.
Infections of the nasal cavities may spread to the:
• Anterior cranial fossa through the cribriform plate.
• Nasopharynx and retropharyngeal soft tissues.
• Middle ear through the pharyngotympanic tube
(auditory tube), which connects the tympanic cavity
and nasopharynx.
• Paranasal sinuses.
• Lacrimal apparatus and conjunctiva
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Applied anaomy- Epistaxis
• Epistaxis (nosebleed) is relatively common because
of the rich blood supply to the nasal mucosa. In most
cases, the cause is trauma and the bleeding is from an
area in the anterior third of the.
• Epistaxis is also associated with infections and
hypertension. Spurting of blood from the nose
results from rupture of arteries.
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Paranasal Sinuses
• The paranasal sinuses are air-filled extensions of the
respiratory part of the nasal cavity into the following
cranial bones: frontal, ethmoid, sphenoid, and maxilla
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Applied anatomy -Sinusitis
• Because the paranasal sinuses are continuous with the
nasal cavities through apertures that open into them,
infection may spread from the nasal cavities,
producing inflammation and swelling of the mucosa
of the sinuses (sinusitis) and local pain. Sometimes
several sinuses are inflamed (pansinusitis), and the
swelling of the mucosa may block one or more
openings of the sinuses into the nasal cavities.
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