The Orbit (Go OD's Go!) Flashcards
What is a blow-out fracture?
Fracture of the orbital floor, usually due to blunt or penetrating trauma
What are the seven bones of the orbit?
Ethmoid Lacrimal Palatine Frontal Sphenoid Zygomatic Maxilla
What bones form the superior wall of the orbit?
Orbital part of the frontal bone
Less wing of sphenoid
What bones form the medial wall of the orbit?
Orbital plate of ethmoid bone
Frontal process of maxilla
Lacrimal bone
Sphenoid bone
What bones form the lateral wall of the orbit?
Frontal process of zygomatic
Greater wing of sphenoid
What bones form the inferior wall of the orbit?
Maxilla
Zygomatic
Palatine
Which wall of the orbit is the thickest and strongest wall?
Lateral wall
Tell me about the orbital septum
A fibrous membrane that becomes continuous with the periosteum of the orbital margins. It is crucial to infection prevention into the orbit
The nasolacrimal duct conveys lacrimal fluid from the __________ to the ___________.
Lacrimal sac; inferior nasal meatus
Levator palpebrae superioris O: I: N: A:
O: lesser wing of sphenoid
I: super tarsus and skin of upper lid
N: CN III - superior division
A: elevation of upper eyelid
Superior Rectus O: I: N: A:
O: common tendinous ring
I: anterosup half of eye
N: CN III - superior division
A: elevation, intorsion, adduction
Inferior Rectus O: I: N: A:
O: common tendinous rings
I: anteroinf half of eye
N: CN III - inferior division
A: depression, Extorsion, adduction
Medial Rectus O: I: N: A:
O: common tendinous ring
I: anteromedial half of eye
N: CN III - inferior division
A: adduction
Lateral Rectus O: I: N: A:
O: common tendinous ring
I: anterolateral half of eye
N: CN VI
A: abduction
Superior oblique O: I: N: A:
O: body of sphenoid
I: sclera deep to superior Rectus
N: CN IV
A: intorsion, depression, abduction
Inferior oblique O: I: N: A:
O: anteromedial floor of orbit
I: sclera deep to lateral Rectus
N: CN III - inferior division
A: extorsion, elevation, abduction
The superior oblique, inferior oblique and lateral Rectus hold the eye where?
Abducted
How do the SO and IO keep the eye aligned on its axis?
Adducting the eye
How do you test the IO and SO using he H test?
Have patient direct eyes medially Look UP (IO) Look DOWN (SO)
How do the SR, MR and IR hold the eye?
Adducted
How do the SR and IR keep the eye aligned with its axis?
By abducting the eye
How can the H test be used to test the SR and IR?
Patient looks laterally Look UP (SR) Look DOWN (IR)
What does RADSIN stand for?
Recti adduct; superiors intort
What happens to the eye when there is a CN III nerve palsy? What might be the cause?
Eye is down and out
Pupil dilated
Complete ptosis
Suspect aneurism (usually in PCA)
What happens to the eye when there is a CN IV nerve palsy? What is a common cause of this?
Eye is hyper
Head tilt to opposite side of palsy
Congenital or traumatic etiology
What happens to the eye in a CN VI palsy? What are the common causes of this?
Eye is deviated toward nose
Common etiology includes trauma, elevated ICP and ischemia from DM
Blood supply to the eye comes from where?
The ophthalmic artery which is a branch of the ICA
Name the 10 branches of the ophthalmic artery.
Lacrimal a Central retinal a Long/short posterior ciliary aa Supra orbital Supra trochlear Medial palpebral aa Ant/post ethmoidal Dorsal nasal
Where does the lacrimal artery supply blood too?
To lacrimal gland
Where does the central retinal artery supply blood to and from what structure does it pierce?
Pierces CN II and perfuses the retina
Where does the long posterior ciliary arteries supply blood too?
Ciliary body and iris
Where does the short posterior ciliary arteries supply blood too?
Choroid
Where do the supra orbital and supra trochlear arteries supply blood too?
Forehead and anterior scalp
Where do the medial palpebral arteries supply blood too?
Contribute to arcades in upper and lower eyelids
Where does the anterior ethmoidal artery supply blood too?
Ethmoidal air cells
Frontal sinus
Nasal cavity
External nose
Where does the posterior ethmoidal artery supply blood too?
Ethmoidal sinuses and nasal cavity
Where does the dorsal nasal artery supply blood too?
Terminal branch to root of nose and lacrimal sac
What is the venous drainage of the eye?
The superior and inferior ophthalmic veins
List the 3 layers of the eyeball and their main components
Fibrous layer: sclera and cornea
Vascular layer: choroid, ciliary body, iris
Sensory layer: retina
What do the superior and inferior ophthalmic veins drain into?
The cavernous sinus
Map the pathway of aqueous humor from creation to drainage.
Ciliary processes secrete > posterior chamber > pupil > anterior chamber > trabecular Meshwork > scleral venous channels
In what way do dilator pupillae fibers oriented?
A radial manner
What is the dilator pupillae innervated by?
By the sympathetic system thus causing mydriasis
In what way are the sphincter pupillae fibers oriented?
Circumferentially
How is the sphincter pupillae innervated?
It is innervated by postganglionic parasympathetic fibers causing miosis.
What is the intraocular lens composed of?
Water and proteins
What component of the lens breaks down in cataracts?
Breakdown of the lens proteins
The vitreous is mainly composed of what?
Water and collagen
What does the vitreous have none of!
BLOOD VESSELS!!!!!
What is the anterior chamber located between?
The iris and the cornea
How does the central retinal vein drain the eye?
Drains retina > leaves through CN II > drains into sup. ophthalmic vein
How do the Vorticose veins drain the eye?
Usually four in number, one for each quadrant of the choroid. Pierced the sclera and drains into the sup and inf ophthalmic veins
Map the pathway of lacrimal gland innervation (efferent)
GE fibers travel from CN II > greater petrosal > n of pterygoid canal > pterygopalatine ganglion > hitchhike with v2 branch > infraorbital fissure > lacrimal (v1) > lacrimal gland
What happens when the ciliary muscle contracts?
The size of the ciliary body decreases, causing a loosening of the zonular fibers, causing the intraocular lens to thicken for accommodation.
What are the three types of tears?
Basal
Reflex
Emotional
What is the purpose/cause of basal tearing?
Lubrication
Cleaning
Removal of bacteria
Normal parasympathetic stimulation
What is the purpose/cause of reflex tearing?
Irritation
Wash irritants from cornea
Afferent = trigeminal Efferent = facial
What is the purpose/cause of emotional tearing?
Emotional stress
Cause unknown
What happens to lacrimation when there is a lesion of CN VII proximal to the geniculate ganglion?
All lacrimation is lost but sometimes the lubrication can be maintained via tarsal, sebaceous and conjunctival glands
What will happen to lacrimation when there is a legion at CN V?
Reflex lacrimation is gone
