Flashcards in Orbit Deck (60):
Which bones form the posterior, superior, inferior, medial, and lateral walls of the orbit?
Posterior wall - sphenoid bone
Superior wall - frontal bone
Inferior wall - maxillary and zygomatic bones
Medial wall - palatine, ethmoid and lacrimal bones
Lateral wall - zygomatic bone
From where in the skull do most structures enter the orbit? What are the two routes of entry?
Most structures enter from the middle cranial fossa through the optic canal and superior orbital fissure.
Which bone forms the optic canal? What runs through it?
The optic canal is in the base of the lesser wing of the sphenoid bone. The optic nerve (CN II) and the ophthalmic artery run through it.
Which bone forms the superior orbital fissure? What runs through it?
The fissure is between the greater and lesser wings of the sphenoid bone. CNs III, IV, V1, VI, and ophthalmic veins run through it.
The inferior orbital fissure is found between the ______ and ______ bones and it connects the ________ and ________ fossae with the orbit.
It is found between the sphenoid and maxillary bones and it connects both the pterygopalatine fossa and infratemporal fossa with the orbit.
What is a blowout fracture?
Fracture of the bones of the medial orbit (they are thin!) that allows for protrusion of orbital contents into the nasal cavity medially or maxillary sinus inferiorly.
Which cranial fossa is the orbit located above?
What is the difference between sclera and conjunctiva?
Sclera is the white of the eye, conjunctiva is a membrane that covers the sclera and it produces mucus and tears.
What is found within the anterior chamber of the eye?
Name the three layers of the posterior 5/6 of the eye (the eye that doesn't include the cornea, lens, ciliary body, and stuff) from outside to inside.
Sclera, choroid, retina
Cataracts are clouding of the _______.
What are tarsal plates?
Fibrous CT that makes up the "skeleton" of the eyelids.
Compare Meibomian glands to Glands of Zeis.
Meibomian glands are located on the backside of the eyelids deep to the tarsal plate. They make meibum - oil that prevents evaporation of the film of tears over the eyes.
Glands of Zeis are located on the tips of the eyelids. These sebaceous glands secrete oily stuff on to the eyelashes.
What causes dry eyes?
Dysfunction of Meibomian glands.
What does inflammation of Meibomian glands cause?
What does inflammation of Glands of Zeis cause?
Meibomian gland inflammation = internal stye aka chalazion.
Glands of Zeis inflammation = external stye aka hordeolum.
What is conjunctivitis? What is blepharitis?
Conjunctivitis is inflammation of the conjunctiva from viral or bacterial infection or allergies.
Blepharitis is inflammation of the eyelids, usually caused by bacterial infection.
What is the lacrimal caruncle?
The funky looking thing at the medial angle of the eye that makes tears/mucus for lubrication.
What is the difference between bulbar conjunctiva and palpebral conjunctiva?
Bulbar is the part of the conjunctiva that covers the sclera and the palbebral conjunctiva is deep to the eyelids.
Tears produced by the lacrimal gland on the lateral side of the eye is swept to the medial side by the _______. How are the tears drained from the eye?
swept over by the eyelids.
Collected by puncta --> lacrimal canaliculi --> lacrimal sac --> lacrimal duct --> nasal cavity via inferior meatus.
Describe the pathway of innervation to the lacrimal gland.
Cell bodies in the superior salivaroty nucleus --> piggyback CN VII motor fibers through the facial canal --> split off anteriorly and meet up with the DEEP petrosal nerve (postganglionic sympathetic from the internal carotid a.), forming the vidian nerve --> through the vidian canal into the pterygopalatine fossa where parasympathetics from the greater petrosal synapse at the pterygopalatine ganglion --> postganglionic parasympathetic fibers hop on V1 and V2, then finally on the lacrimal nerve (V1) to the lacrimal gland.
Describe the pathway of sympathetic innervation to the lacrimal gland.
Cell bodies in spinal segments T1-T4 send fibers superiorly --> synapse at superior cervical ganglion --> hop on the internal carotid artery --> join the greater petrosal nerve to form the Vidian nerve --> vidian canal --> pterygopalatine fossa --> hop on V1 and V2 --> hop on lacrimal nerve to the lacrimal gland.
What does the lacrimal nerve (V1) do aside from giving autonomic fibers a ride to the lacrimal gland?
Sensory for the skin of the upper lateral eyelid
Does sympathetic innervation of the lacrimal gland have a large effect?
Not really, tears are good.
What is Tenon's capsule? What lines the orbit?
A membrane that surrounds the back of the eye and optic nerve, separating them from the periorbital fat. Periorbital fascia lines the orbit and reflects over extraocular muscles.
What are Check ligaments?
Medial and lateral thickenings of Tenon's capsule that prevent excessive eye rotation.
How does Grave's disease cause exophthalmos?
Abnormal Abs target fibroblasts in the orbit --> differentiation into fat cells --> fat cells, muscles expand and get inflamed.
From what structure do most of the extraocular muscles originate? Which extraocular muscle does NOT originate from this?
Tendinous ring of Zinn. All muscles except the inferior oblique muscle attaches to it - instead it originates from the floor of the orbit.
Which nerves pass through the tendinous ring of Zinn? Which ones do not?
CNs II, III, VI pass through it.
CN IV and V1 pass above it.
Describe the innervation to all the extraocular muscles.
CN III (oculomotor) does it all except 2:
CN IV (trochlear) does superior oblique muscle. The nerve is named after the trochlea, the pulley that the muscle runs through.
CN VI (abducens) does the lateral rectus m - acts to abduct the eye (hence abducens).
Which muscle is responsible for reflexively opening your eyes wide when you get startled?
The levator palpebrae superioris has smooth muscle mixed in (superior tarsal muscle - Muller's muscle) that is innervated by sympathetic fibers.
What are the six eye movements?
Abduction, adduction, elevation, depression, extortion, and intorsion.
Starting at primary gaze, what movements does contraction of the superior rectus and inferior rectus muscles produce, respectively?
The superior rectus moves the eye up and in because when in primary gaze, the majority of its fibers are aligned medially to the axis of the muscle itself.
The inferior rectus moves the eye down and in for the same reason.
When acting by themselves, what eye movements are produced by contraction of the oblique muscles?
The superior oblique muscle moves the eye down and out because its acts from its superomedial sling, inserting on the upper lateral posterior quadrant of the eye.
The inferior oblique moves the eye up and out because it originates in the inferomedial orbit and inserts on the lower lateral posterior quadrant of the eye.
Do the extraocular muscles pierce Tenon's capsule to attach to the eye?
What muscles need to contract to truly elevate and depress the eye when in primary gaze, respectively?
To elevate, the superior rectus and inferior oblique muscles would need to contract at the same time.
To depress, the inferior rectus and superior oblique muscles would need to contract at the same time.
How can you clinically test CN IV (trochlear nerve - supplies the superior oblique m.)?
Have the patient look IN, then DOWN
What is strabismus?
When the eyes are not aligned properly.
What do the parasympathetic fibers that travel with CN III innervate?
The constrictor pupillae muscle and the ciliaris muscle.
Describe the three clinical signs of damage to the oculomotor nerve (CN III).
1. Only the lateral rectus (CN VI) and superior oblique (CN IV) would work, pulling the eye out and down.
2. Ptosis due to paralysis to the levator palpebrae superioris muscle.
3. Dilated pupil due to absence of parasympathetic stimulation to the constrictor pupillae m.
Which nerve supplies sensation to the cornea and sclera of the eye?
Nasociliary branch of V1, specifically the long and short ciliary nerves.
What types of fibers are carried in the long and short ciliary nerves, respectively?
Long has sensory and sympathetic fibers.
Short has sensory, sympathetic, and parasympathetic fibers (they go through the ciliary ganglion).
Describe the neural pathway of the corneal (blink) reflex.
Afferent signal supplied by short and long ciliary nerves (V1), efferent signal to the obicularis oculi (CN VII facial nerve) closes the eye.
Why would an anuerysm of the internal carotid artery affect lateral movement of the eye?
It is next to CN VI, so an aneurysm can compress that nerve, which supplies the lateral rectus muscle.
Which branch of the autonomic nervous system controls the dilator muscle of the pupil? What about the constrictor (sphincter) muscle of the pupil?
Dilator muscle is under sympathetic control.
Constrictor is under parasympathetic control (CN III)
Describe the neural pathway of parasympathetic innervation to the eye.
Edinger-Westphal nucleus has parasympathetic preganglionic cell bodies --> hop on motor fibers of CN III (oculomotor n.) --> follow the inferior division of CN III after passing through superior orbital fissure --> ciliary ganglion --> synapse happens --> postganglionics travel along the short ciliary nerves (V1) to supply sphincter pupillary muscle (pupil constriction) and ciliary muscles (accomodation).
Describe the neural pathway of sympathetic innervation to the eye.
Cell bodies are in paravertebral ganglia from T1-T4 --> synapse at superior cervical ganglion --> form the deep petrosal that joins the ICA --> hop off to nasociliary nerve (V1) --> hop on long AND short ciliary nerves --> dilator pupillary muscle and superior tarsal muscle.
What is the arrangement of the muscle fibers of the sphincter pupillary muscle, and dilator muscle, respectively?
Sphincter muscle fibers run circumferentially within the iris like a drawsting - contraction narrows the pupil.
Dilator fibers run radially within the iris, contraction widens the pupil.
Explain why both pupils should contract when light is shined in one eye.
Action potentials from the retinal ganglion cells located medially to the optic nerve cross over to the other nerve at the optic chiasm. Therefore, a signal in one eye will relay to both lateral geniculate nuclei --> Edinger-Westphal nuclei --> parasympathetic efferent signal to both sphincter pupillae.
Which arteries in the circle of Willis can compress CN III if they develop an aneurysm?
The posterior communicating artery and superior cerebellar artery
Loss of sympathetic innervation to the eye is called ______ Syndrome. Name four clinical features of this.
1. Miosis (pupillary constriction)
2. Ptosis (loss of sympathetic innervation to smooth muscle in the levator palpebrae superioris - Mueller's muscle)
3. Anhydrosis (no facial sweating)
4. Vasodilation of blood vessels in the face
How is the lens of the eye rounded to see stuff close-up (accomodation)? Which branch of the nervous system does this?
The longitudinal and circular fibers of the ciliary muscle contract to squish the lens (via zonal fibers) into a sphere. The parasympathetic nervous system does this.
Is sympathetic stimulation required to flatten the lens of the eye?
Nope, relaxation of the ciliary muscle (e.g. loss of parasympathetic input) will naturally flatten the lens.
Which artery supplies the orbit? Where does it come from?
Ophthalmic artery, from the circle of Willis (1st branch of the ICA)
Which artery pierces the dura that surrounds the optic nerve to eventually supply the retina?
The central artery of the retina (a branch of the ophthalmic artery).
What happens is the central artery of the retina gets occluded?
There are no anastomoses so that would result in blindness.
What is the macula?
A spot with the highest concentration of retinal cells
What is papilledema?
Swelling of the optic disc usually due to increased intracranial pressure.
Describe the pathogenesis of glaucoma.
Ciliary body (where the ciliary muscle is) produces aqueous humor --> posterior chamber --> anterior chamber --> drainage via canal of Schlemm.
In glaucoma, the canal of Schlemm is blocked --> increased pressure on lens and vitreous humor--> increased pressure on retinal cells --> blindness
What type of tumor may compress the optic chiasm?