eye movement - jullet Flashcards
How do most eye movements occur?
reflexes - which allow the eyes to track objects of interest when the object are moving or when the head is moving
What is vergence?
movement of the eye to focus up close or far away
What is diploia?
double vision
What areas of the brain contribute to the control of eye movements?
retina, vestibular system, cerebral cortex, cerebellum, and superior colliculus
What is extorsion of the eye? Intorsion?
EXTORSION: upper portion of the eye approaches the temporal regions. INTORSION: upper portion of the eye approaches the nose
What is convergence of the eye? Divergence?
CONVERGENCE: pupils move inward, DIVERGENCE: pupils move apart
Every eye muscle has to work with other eye muscles to produce motions of the eye, exept for these two:
medial and lateral rectus
Why is it that every eye muscle has to work with other eye muscles to produce motions of the eye (except M/L rectus)?
because the orbit and muscles of the eye are not directly in line with the visual axis.
What happens if you contract the SR, IR, SO, or IO individually?
torsion and deviation of the eye
If contracted alone, the SUPERIOR RECTUS produces these movements:
elevate, intort, adduct
If contracted alone, the INFERIOR OBLIQUE produces these movements:
elevate, extort, abduct
If contracted alone, the INFERIOR RECTUS produces these movements:
depress, extort, adduct
If contracted alone, the SUPERIOR OBLIQUE produces these movements:
depress, intort, abduct
What two muscles produce pure elevation of the eye?
SR, IO
What two muscles produce pure depression of the eye?
IR, SO
What cranial nerves run in the cavernous sinus?
CN 3, 4, 5, 6
What happens when there is extraocular nerve damage? (3)
1) eyes drifts away from the direction of pull of the muscle innervated by that nerve, since other muscles have tonic activity.
2) Patient perceives double vision, esp when the eyes are moved in the direction requiring activity of the weak muscle.
3) Patient tilts head toward the side of the abnormal eye (to align with the normal eye with the abnormal eye)
Where does GSE and parasympathetic fibers of CN3 originate and emerge?
GSE: oculomotor nucleus (midbrain, ventral to PAG), PARASYMPATHETIC: Edinger-Westphal nucleus (midline, btwn L/R oculomotor nuclei). EMERGES: interpeduncular fossa of the midbrain
What does CN3 innervate? (5)
GSE innervation to: IR, IO, MR, SR (remember LR6, SO4, REST ARE 3) and levator palpebrae
Does CN3 decussate? If so, where does it decussate?
No.
Where does pre & post-ganglionic PARAsympathetic fibers of CN3 synapse to? What function do these fibers serve?
PRE: ciliary ganglion
POST: sphincter pupillae and ciliary muscles. FUNCTION: accomodation
Parasympathetic nerve fibers of CN3 run in the outer parts of the nerve. How does this affect the properties of the fibers?
it makes it MORE sensitive to external compression and LESS sensitive to ischemic damage.
CN3 is sandwiched between these two structures in this region of the brain.
Interpeduncular fossa. Superior cerebellar a. and post-cerebral a.
What happens if you compress CN3?
pupillary dilation (remember that parasympathetic fibers run on the outer parts of the nerve, and they function to constrict the pupil)
What do parasympathetic nerve fibers of CN3 function in? (2)
1) motor limb of the light reflex (constrict the pupil)
2) accomodation for close-up vision
What structures are involved the pupillary light reflex? (5)
1) optic nerve
2) optic chiasm
3) optic tract
4) pretectal nuclei
5) Edinger-Westphal nucleus
What is oculomotor nerve palsy?
severe damage to CN3 such that the individual is unable to maintain normal alignment of their eyes when looking straight ahead, leading to strabismus and, as a consequence, double vision (diplopia).
What is one cause of oculomotor nerve palsy?
aneurysm of posterior communicating artery
Where does CN4 originate and emerge?
GSE: trochlear nucleus.
EMERGES: caudal midbrain (dorsum of brainstem, at the ponto-mesencephalic junction) and wraps around the brainstem
What does CN4 innervate?
SO (remember LR6, SO4, REST ARE 3)
Does CN4 decussate? If so, where does it decussate?
Yes. Midbrain
What happens if there is a CN4 lesion?
eye deviates slightly medial and extorts
Where does CN6 originate and emerge?
GSE: abducens nucleus (in the facial colliculus).
EMERGES: caudal pons (at the medullary-pontine junction)
What does CN6 innervate?
LR (remember LR6, SO4, REST ARE 3)
Does CN6 decussate? If so, where does it decussate?
No.
What are some landmarks of CN6 as it emerges from the abducens nucleus to innervate LR? (2)
1) travels through the cavernous sinus
2) crosses the ICA
What happens to the activity levels of extraoculi nuclei during saccadic eye movements?
resting tone -> burst of activity -> reset at new resting tone
Why is there a 200ms delay between movement of the target position and the eye position?
process the eye movement to assure that it’s accurate
What happens to the activity of the extraoculi nuclei during saccadic eye movements during ABDUCTION? ADDUCTION?
ABDUCTION: increase in firing rate of motor neurons.
ADDUCTION: decrease
What are saccades?
rapid, ballistic eye movements that occur so fast that the eye cannot see during the movement; used to catch up with an old target that has suddenly moved
T/F During saccades, the vision completely blurs.
True. This happens because these rapid jumps occur so fast
What produces the saccade movements? (2)
PPRF (for horizontal saccades) + superior colliculus.
Where does the superior colliculus project to for HORIZONTAL eye movements? VERTICAL?
HORIZONTAL: PPRF
VERTICAL: Rostral interstitial nucleus
What are microsaccades? What is the purpose of them?
minute, imperceptible movements of the eye that keep an image from remaining on the same retinal cells for too long (avoids adaptation)
What type of movement is voluntary conjugate horizontal gaze?
saccadic eye movement
How is voluntary conjugate horizontal gaze initiated? Where does it project to?
Frontal eye field of cerebral cortex (Brodmann’s area 8)»_space; IPSI superior colliculus + CONTRA PPRF.
Where are the neurons that are critical for generating voluntary horizontal gaze located?
PPRF
Describe how a LEFT lateral gaze occurs.
RIGHT frontal eye field of cerebral cortex»_space; RIGHT superior colliculus + LEFT PPRF»_space; LEFT PPRF projects to LEFT abducens nucleus, which gives rise to L CN VI and fibers that travel via MLF to RIGHT oculomotor nucleus to give rise to CV III»_space; L CN VI projects to L lateral rectus and R CN III projects to R medial rectus
What type of lateral eye movements occur with activation of the R frontal eye field?
LEFT - away from the frontal eye field that initiated the process and toward the side of het PPRF that was involved in the movement (see pg. 28 if confused)
What is the frontal eye field?
part of the pre-motor cortex that patterns voluntary horizontal gaze. Activation of the L frontal eye field would move the eyes conjugately to the R
Where does the frontal eye field project to? (2)
superior colliculus and PPRF
What is the functional significance of the superior colliculus? Where does it project to?
site of relay of cortical control of eye movement. PPRF
Where does the PPRF project to?
ipsilateral abducens nucleus
Where does the abducens nucleus project to? (2)
Ipsilateral CN VI and contralateral CN III via MLF
What is Broadmann’s area 8?
Frontal eye field of cerebral cortex that projects to IPSI superior colliculus + CONTRA PPRF.
What afferents do the superior colliculus receive? (4)
1) retina (vision)
2) inferior colliculus (sound)
3) spinal cord (somatic sensations)
4) cerebral cortex
What are the efferents of the superior colliculus? (3)
1) spinal cord (tectospinal tract)
2) brainstem - PPRF (tectoreticular)
3) brainstem - midbrain reticular formation (RF, tectoreticular)
What happens if you stimulate the superior colliculus?
triggers eye + head movements towards the stimuli of interest
How is the superior colliculus organized?
visual inputs = superficial; motor cells = deep
What happens if you have a lesion in PPRF?
no voluntary, horizontal gaze toward side of damage
What does the MLF contain? (5)
crossed and uncrossed ascending projections from:
1) abducens nuclei
2) trochlear nuclei
3) oculomotor nuclei
4) PPRF
5) vestibular nuclei
What happens if you damage the MLF? How does this affect eye movement?
Ophthalmoplegia-lateral movement of one eye is not followed by medial movement of the other eye; lateral-moving eye also has nystagmus
Where do signals for voluntary vertical eye movements arise?
diffuse areas of the cerebral cortex
Describe how VERTICAL eye movements occur.
Diffuse areas of the cerebral cortex»_space; Rostral interstitial nucleus (vertical gaze center)»_space; Posterior commissure + CN III and CN IV
What constitutes the vertical gaze center? (2)
1) rostral mesencephalic reticular formation
2) rostral interstitial nucleus of MLF
What happens if you damage the rostral interstitial nucleus of MLF or the posterior commissure?
no voluntary, vertical upgaze. BUT note that the upward reflex movements of the eye to vestibular stimuli still occurs
What is Parinaud Syndrome?
direct or compressive injury to the dorsal midbrain - causes paralysis of voluntary UPgaze, with downward gaze is usually preserved
What is Progressive Supranuclear Palsy?
degeneration of rostral interstitial nucleus (vertical gaze center) in the rostral midbrain - causes paralysis of voluntary UP- and down-gaze
What is the vestibulo-ocular reflex?
produces smooth, NON-saccadic eye movements in response to changes in head position (allows the eye to remain focused on a target when the head moves)
Describe how the vestibulo-ocular reflex occurs.
CN 8 projects to vestibular nucleus + flocculus. Vestibular nucleus projects to CN 6 and PPRF, which then projects to CN 3 and CN 4 via MLF
What happens if there is damage to the vestibular connections of the vestibular-ocular reflex?
drift of the eyes, as if the head was moving, which triggers rapid saccadic eye movements to return the eyes to their original target (nystagmus)
When do eyes move slowly? (2) What pathway does this involve? What is this called?
eyes move smoothly only when 1) you are tracking something, or 2) the head is moving. Involves the vestibulo-ocular reflex pathway. Called smooth pursuit/tracking
Describe how smooth pursuit/tracking occurs?
occpital eye field»_space; frontal eye field + pontine nuclei (ipsi)»_space; flocculus (contra) via middle cerebellar peduncle)»_space; vestibular complex (ipsi) via inferior cerebellar peduncle»_space; CN 6 + PPRF»_space; CN 3 + CN4 via MLF
What’s required for smooth pursuit/tracking to occur?
awareness of a moving visual stimulus (in region of the visual association areas in the occpital lobe)
What reflex pathway is used in smooth pursuit?
vestibulo-ocular reflex (vestibular complex (ipsi) via inferior cerebellar peduncle»_space; CN 6 + PPRF»_space; CN 3 + CN4 via MLF)
What is the fixation reflex?
ability to fixate on moving target (complements vestibulo-ocular reflex to stabilize the eyes
What is the optokinetic reflex?
aka “optokinetic nystagmus” - an involuntary fixation on ojects that are moving in relationship to the head (ie looking out of a moving vehicle) - the eyes will track the object involuntarily for a distance and then saccade to the opposite side to reacquire the target.
What happens to the optokinetic reflex if one side of the visual cortex is damaged?
optokinetic nystagmus will be LOST when objects move TOWARD the side of the cortical lesion (ie away from the side of the vision loss)
What is the vergence reflex?
convergence or divergence of the eyes to focus up close or off into the distance
What structures/pathways are involved in the vergence reflex? (3)
1) occipital projections to vergence center in mesencephalic RF
2) superior colliculus
3) wired in parallel with accomodation
How is the vergence reflex wired in parallel with accomodation?
pupillary constriction with contraction of ciliary muscle occurs at the same time to allow for close focus
What is the pupillary light reflex?
consensual reflex where there is bilateral constriction of the eye in response to light stimuli
Describe how the pupillary light reflex works.
Light»_space; R retina»_space; R pretectal nuclei»_space; bilateral projections to the R/L Edinger-Westphal nucleus»_space; pupillary constriction via CN III (bilateral response)
What is partial third nerve palsy?
deficit in CN III that can can affect the SR, IR, MR, IO, levator palprebrae, or the parasympathetic fibers
How does partial third nerve palsy affect the pupillary light reflex?
parasympathetic fibers act to constrict the pupils in response to light; if these fibers are affected, you won’t get a pupillary/consensual reflex in response to light
What is the Marcus-Gunn pupil?
a situation where the pupils of an affected eye will constrict LESS (and appear to DILATE)
What is nystagmus? When is it normal? When is it abnormal?
rapidly oscillating eye movements that are NORMAL at the END of the visual range, but ABNORMAL when it occurs spontaneously in them MIDDLE of the visual range
What is jerk nystagmus?
rapid + slow oscillating eye movements (but described in terms of the FAST component).
What are some causes of jerk nystagmus? (5)
damage to:
1) flocculus
2) vestibular nuclei
3) MLF
4) vestibular receptors in inner ear
5) vestibular nerves
What is pendular nystagmus?
when the oscillations are equal in both directions (sinusoidal oscillations) but may occur in any direction (torsional, horizontal, vertical, or a combination of these)
