Lec 21 Eye Movements Flashcards
What is the relationship between the pulling directions of extraocular eye muscles and the planes of semicircular canals?
same plane
What muscles are reponsible for horizontal eye movements?
- only medial and lateral rectus
What muscles are responsible for vertical eye movement?
SR, IR, SO, IO
elevation = SR and IO depression = IR and SO
What muscles control torsion when eye is abducted?
superior oblique = intorsion [top of eye toward nose]
inferior oblique = extorsion [top of eye away from nose]
What muscles control torsion when eye is adducted?
superior rectus controls intorsion [top of eye toward nose]
inferior rectus controls extorsion [top of eye away from nose]
Where are the oculomotor nuclei located?
in midbrain at level of superior colliculi
What does the oculomotor nerve innervate?
- medial, superior, inferior recti
- inferior oblique
- levator palpebrae
- caries parasympathetic from edinger-westphal nucleus to ciliary ganglion to innervate pupillary sphincter
What does the trochlear nerve innervate?
superior oblique
– nerve nuclei is contralateral to the eye it innervates
What does the abducens innervate?
lateral rectus
What are clinical signs when 3rd nerve function completely eliminated?
- ptosis [lid is closed]
- eye “down and out”
- pupil dilated [mydriasis]
- eye nonreactive to light
- loss of accomodation
- impaired elevation, depression, adduction [b/c weak medial rectus]
What is common cause of 3rd nerve palsy?
- aneurysm of posterior communicating artery
- uncal herniation
What is emergency sign of impending brain herniation?
- hutchinson pupil –> dilated non-reactive pupil caused by compression of 3rd nerve by herniation of temporal lobe uncus
Where are the paired trochlear nuclei located?
- close to ventromedial edge of periaqueductal gray in midbrain
- at level of inferior colliculi
What are signs of CN 4 dysfunction?
- elevation of affected eye [hypertropia]
- vertical diplopia [double vision]
- may present with head tilt in direction of the affected eye
what is path of oculomotor nerve?
- exits ventral in midbrain, passes between PCA/SCA through cavernous sinus to superior orbital fissure
what is path of CN4?
exits dorsally from midbrain and decussates
then through cavernous sinus to superior orbital fissure
What is the origin of CN4 dysfunction?
- head trauma
- congenital defect
Where is abducens nuclei located?
lower pons / floor of 4th ventricle at facial genu/colliculus
What is path of abducens nerve?
exits nucleus in pons, passes under gruber’s ligament
through cavernous sinus to superior orbital fissure
What are signs of abducens nerve dysfunction?
- medially directed eye [can’t adduct] on ipsilateral side
- deviation of eye toward one another [esotropia]
Where is lesion likely to be if oculomotor, trochlear, and abducens all affected in one eye? how can you determine?
- likely either orbital apex or cavernous sinus
if orbital apex –> optic nerve also affected so loss of vision
if cavernous –> no vision loss
What is the medial longitudinal fasiculus? function?
MLF = bilateral fiber tract along cerebral aqueduct/ ventricle 4
- used by interneurons of abducens 6 nucleus to synapse on contralateral medial rectus subnucleus of CN 3
- facilitates conjugate horizontal eye movements [can coordinate simultaneous contraction of ipsilateral LR and contralateral MR]
What two types of neurons are in the abducens nucleus?
- lower motor neurons
- internuclear neurons
What nerves does the part of MLF rostral to abducens nucleus interconnect?
- vestibular nuclei
- nuclei of 3, 4, 6
What happens if damage to MLF either in midbrain or pons?
internuclear ophthalmoplegia [INO]
What are classic signs of a unilateral INO [internuclear opthalmoplegia]?
when try to turn gaze toward contralateral side
- can’t adduct ipsilateral eye, nystagmus of contralateral abducting eye
- preserved vergence: ipsilateral adducting during disconjugate movements
What happens in lesions of abducens nerve or PPRF?
ipsilateral lateral gaze palsy
- imparied conjugate gaze in both eyes to the side of the lesion
ex. if lesion on left side
when try to turn gaze left –> nothing happens
What do you see in lateral gaze palsy?
impaired conjugate gaze in both eye to the side of the lesion
What can cause a lateral gaze palsy?
- unilateral lesion of PPRF
Where do eye movement command signals originate from?
UPMs in cortical eye fields primarily in frontal and parietal lobes then to:
–> anterior limb/genu of internal capsule
–> MLF
What is sign of lesions [stroke] that destroys a cortical eye field?
- ipsilateral gaze deviation [gaze preference]
= looks at the lesion
What is saccade?
conjugate eye movement
- rapid eye movement focusing fovea on stimuli
- used to shift gaze
2 saccade gaze centers = PPRF + riMLF
what is optokinetic nystagmus?
- conjugate
- back and forth beating eye movement
- direction of nystagmus is always named for the quick phase [the quick reflexive glances in oppsoite direction from eye movement]
what is vestibulo-ocular reflex?
- eyes move in opposite direction of head rotation to maintain focus on target
What is vergence?
disconjugate eye movement
- allows eyes to focus on near [convergence] or far [divergence] objects
path of VOR action if head turns to left?
head turns to left –> endolymph in left horizontal canal shifts forward, activates canal nerve
- -> projects to ipsilateral vestibular nucleus –> sends excitatory to contralateral abducens nucleus and [via MLF] ipsilateral oculomotor nucleus
- -> inhibitory fibers from the vestibular nuclei project to ipsilateral abducens nucleus –> inhibition in ipsilateral LR and contra MR
What is caloric testing?
- test integrity of each horizontal canal
warm water into external auditory meatus –> mimicks head turn to ipsilateral side –> both eyes go toward contralateral ear then reset with nystagmus back toward ipsilateral [quick phase of nystagmus toward ipsilateral ear]
cold –> decreases nerve firing rate –> eyes move toward ipsilateral –> reset with nystagmus toward contralateral [quick phase of nystagmus toward contralateral ear]
COWS: cold opposite, warm same side
What is smooth pursuit?
conjugate
- to maintain stable retinal image of moving target
velocity matches stimulus velocity
Which eye muscle for down and in?
superior oblique
What is unique about levator palpebrae superioris innervation?
bilateral supply rather than ipsilateral like all other eye muscles supplied by extraocular
What is pathway for horizontal saccade?
cortical eye fields –> superior colliculus –> pprf –> ipsilateral avducens nucleus –> ipsilateral lateral rectus + contralateral media rectus [via MLF]
What are the saccadic gaze centers?
pprf = paramedian pontine reticular formation for horizontal
riMLF = rostral interstitial nucleus of the MLF for vertical
what is pathway for vertical saccade?
cortical eye fields –> superior colliculus –> riMLF –> motor neurons of CN 3 and r [SO/IO/SR/IR]
What is the pathway for smooth pursuit?
descending project form cerebral cortex –> pontine nuclei –> cerebellum –> vestibular nuclei –> oculomotor nuclei
