week 2- eye Flashcards
Decribe the four Layers of Fascia of the eye orbit
- periorbita & orbital septum & common tendonous ring
- bulbar sheath
- Fascia surrounding the extraocular muscles and recti to form check ligaments
- meningeal dura
Why does one see papilledema with increased ICP
the meningeal dura surrounds the optic nerve, arachnoid and pia and is continuous with the sclera. Consequently, when there is increased intracranial pressure, axoplasmic flow from the axons of the optic nerve is restricted, and they become swollen at the optic disc (papilledema)
define chalazion
Blockage and inflammation of a tarsal gland
Tarsal plates are associated with glands (tarsal glands).
what are the three muscles of the eyelid
- Levator palpebrae superioris
- Superior tarsal muscle
- Orbicularis oculi
what is the innervation of the eye muscles
- Levator palpebrae superioris-
CNIII
- Superior tarsal muscle-
sympathetic fibers
- Orbicularis oculi-
CNVII
what provides special and general sensory information to the eye
CN II optic- special sensory
CN V1- general sensory
What are the branches of V1
NFL
- Nasociliary
- Frontal
- Lacrimal
name the branches of the frontal nerve and what it innervates
supraorbital and supratrochlear nerves
Supraorbital=>brow, forehead, parts of scalp
Supratrochlear=> medial upper lid and forehead
the frontal nerve is a branch of the trigemmenal
what does the lacriminal nerve supply
lacrimal gland, Conjunctiva, lateral superior eyelid
Supplies innervation to the lacrimal gland—parasympathetics via greater petrosal n (CNVII) hitch a ride on this nerve
The lacrimal nerve runs along the lateral wall above the lateral rectus, supplies the lacrimal gland* and lateral upper lid
what are the branches of the nasocilary n and what does it supply
PLICA: posterior ethmoid, long ciliary, infratrochlear,communicating branch to ciliary ganglion, anterior ethmoid
- Anterior and posterior ethmoidal nerves: to sinuses and nasal cavity
- Long ciliary nerve: cornea, conjunctiva; sympathetic fibers to dilator pupillae, afferent limb of corneal blink reflex.
- Infra trochlear nerve: skin of medial eyelids, tip of nose, conjunctiva, lacrimal sac
- communicatingbranchto ciliary ganglion- sensory root
what innervates the corneal blink reflex
long cilliary branch of the nasocilliary nerve
wht provides parasympathetic innervation to the eye orbit
CN III and VII provide parasympathetic innervation to the orbit; these parasympatheticsalways travel on a branch of CN V.
review the anatomy of the cavernous sinus and the neurovasculature commonly impacted by a cavernous sinus thrombosis
O - oculomotor nerve
T - trochlear nerve
O - ophthalmic branch of trigeminal nerve
M - maxillary branch of trigeminal nerve
C - internal carotid artery
A - abducensnerve*
(T - trochlear nerve again)
O TOM CAT
ID the 2 branches of CN III and the muscles they innervate and which one carries PNS and SNS fibers
Superior branch
- levator palpebrae superioris
- superior rectus
- carries SNS fibers that innervate a smooth muscle(the superior tarsalm)
Inferior branch
medial and inferior rectus & inferior oblique
preganglionic PSNS to ciliary ganglion (visceromotor)
what can cause ptosis
Loss of function of either the levator palpebrae superioris (PNS) or superior tarsal muscle (SNS) results in a ptosis of the upper eyelid. Thus, ptosis may be caused by either CNIII or sympathetic damage.
Why is the position of PSNS fibers relative to CNV fibers clinically relevant? Third nerve palsies are often caused by aneurysms. This aneurysm will compress the parasympathetics first, and you will see a blown pupil before you see mm effects.
and aneurysm at junction of Pcomm(posterior communicating) & ICA
what are third nerve palsies typically caused by
aneurysm that will compress the parasympathetics first, and you will see a blown pupil before you see mm effects. Because of PSNS fibers relative to CNV fibers CNV is also impacted
what are the 3 sympathetics targets in the eye how to they reach their target
- Pupillary dilator
- Superior tarsal muscle
- Lacrimal gland
All sympathetics originate in the lateral horn of the spinal cord and synapse in the superior cervical ganglia. Post-ganglionics travel in a plexus surrounding the internal carotid (the carotid plexus), then take a convoluted route
describe the sympathetic path to the lacrimal gland
lateral horn of the spinal cord –> synapse in the superior cervical ganglia –> travel in the carotid plexus –> leave as the deep petrosal nerve + join the greater petrosal nerve–> nerve of the pterygoid canal, and follow the same path as the parasympathetics to the lacrimal gland
Inferior oblique
innervation
action
CN III
elevation, lateral movement and abduction
superior oblique
innervation
action
CN IV
Depression, Abduction, medial eye rotation
lateral rectus
innervation
action
CN VI
abduction
medial rectus
innervation
action
CN III inferior branch
adduction
superior rectus
innervation
action
CN III superior branch
elevation, adduction
inferior rectus
innervation
action
CN III superior branch
depression, adduction
levator palpebrae superioris
CN III superior branch
What cranial nerves carry preganglionic parasympathetic (general visceral efferent) fibers
CNIII, VII, IX, X; CNIII and CNVII carry these into the eye or orbit
what characterizes trochlear nerve injury
inability to focus on near objects
what would a lesion of the facial nerve result in
Loss of taste from the anterior two-thirds of the tongue
Partial sensory denervation of the auricle
Increase in loudness of sound
Loss of tear production
what CN is damaged
left LR is unable to move the eye left.
why do you need to conduct an eye exam before a LP
papilledema would indicate increased CSF pressure
Following a partial thyroidectomy a patient presents with signs and symptoms that you believe indicate his cervical sympathetic trunk was inadvertently transected during the procedure. Which of the following would NOT be consistent with your suspicion?
Absence of sweating on forehead
Ptosis
Pupillary constriction
Redness and increased temperature on the forehead
A 10-year-old boy fractures the floor of the right middle cranial fossa in an automobile accident/ Physical examination reveals loss of emotional tearing on the ipsilateral side. What nerve is most likely damaged
1.Greater petrosal. The lacrimal nerve conveys autonomics to the lacrimal gland, but would not be damaged by a fracture of the middle cranial fossa
What nerves enter the orbit through the intraconal space
CNII, IIIi, IIIs, VI and nasociliary
where is CN VI
what does it innervate
why is it suseptible to damage
Abducens nucleusis located in caudal pons, in the facial colliculus. Exits the inferior pontine sulcus, i.e. near midline at ponto-medullary junction. Can be damaged in nucelus or at pontine base due to its track
•contains lower motor neuron cell bodies whose axons (CN VI) innervate lateral rectus
can be damaged because its long and thin
where is the CN IV located
what does it innervate
Nucleus= located in caudal midbrain (caudal to oculomotor nucleus) –> decussates in tectum of midbrain –> exits dorsal midbrain caudal to inferior colliculus –> passes through lateral wall of cavernous sinus & superior orbital fissure
Innervates superior oblique: depresses (infraducts) adducted eye; intortsabducted eye
Nerve encircles midbrain in subarachnoid space
what would you see clinically if CN IV was injured
Eye elevated, extorted
Patient cannot look down & in
vertical diplopia
where is CN III located
what does it innervate
what would you see clinically if it was injured
nucleus is in rostral midbrain
- Parasympathetic nucleus = Edinger-Westphal, located just dorsal
- CN III emerges medially between midbrain and pons (between PCA & SCA) –> lateral wall of cavernous sinus & superior orbital fissure
innervates all extraocular muscles except lateral rectus & superior oblique
eye “down & out”, severe ptosis, dilated pupil… can be caused by aneurysm in pcomma
what are the 3 gaze centers and their location within the brain
vertical gaze (up and down- midbrain- CN III
vergence (converse, diverge)- midbrain- CN III
lateral gaze (horizontal)- midbrain (medial rectus) and pons (lateral rectus)- II and VI
CN III midbrain, CN VI- pons
what occurs when you move the eye to the left
activation of abducens (CN VI) in left pons to move left lateral rectus –> simultaneously a second population of neurons send fiber bundles called medial longitudenal fasiculus (MLF) across the midline and to the left pons sends LMN to midbrain to activate right medial rectus- oculomotor (CN III)
whata are the two bones that form the roof of the orbit
lesser wing of sphenoid, orbital plate of frontal bone
what are the bones that form the lateral wall of the orbit
frontal and orbital surface of the zygomatic bone
greater wing of the sphenoid
what is the strongest wall of the orbit
lateral
Fractures of the lateral orbital wall are usually accompanied by severe facial trauma
most common site for a fx of the lateral wall is the sphenozygomatic suture line
what forms the apex of the orbit and what openings does it have
Sphenoid
- medially: optic canal for optic n./ophthalmic a.
- laterally: superior orbital fissure for a number of nerves (III, IV, V1, VI) & superior ophthalmic v.; it separates the greater and lesser wings of this bone
3.inferior orbital fissure between sphenoid and maxilla: through here brs. of maxillary nerve and artery pass; also veins from deep face region pass through here connecting with veins within orbit
what bones form the floor of the orbit
maxilla
zygomatic bone
palatine bone
what bones form the medial wall of the orbit
lacrimal
ethmoid
lesser wing of sphenoid
what does the lacrimal fossa contain
The lacrimal fossa of the lacrimal boneholds the lacrimal sac NOT the lacrimal gland
ID the nerves passing through the superior orbital fissure
“Live Frankly To See Absolutely No Insult”
Mnemonic for intraconal space
With the exception of the obliques (and levator palpebrae superioris), all extraocular muscles attach to a common tendinous ring. The area defined by the common tendinousring is called the intraconalspace
Mnemonic for intraconal space: NASO2: nasociliary,abducens,sympathetic nn, O2=2 divisions of oculomotor n, superior and inferior
Orbital rim fractures are a relatively common fracture of the orbit. These fractures involves the three bones that form the outer rim of the orbit. What are these bones?
Maxilla, zygomaand frontal
The superior orbital fissure connects the orbit with what cranial fossa
middle
The superior orbital fissure connects the orbit with what cranial fossa
The superior orbital fissure connects the orbit with what cranial fossa
Your patient has a lesion of a nerve outside the intraconalspace. What eye movements will help you determine the integrity of this nerve
.Three nerves are located outside the intraconalspace—frontal, lacrimal and trochlear. Of these, only one is a motor nerve (trochlear). The trochlear nerve innervates the superior oblique muscle. To check the integrity of the SO, ask the patient to look inward (toward the nose) and down.
