control of eye movement Flashcards
What do normal eye movements require?
- head movement (vestibular info)
- visual objects (vision)
- eye movement and position (proprioceptive info) - LMN
- selection of a visual target (brainstem and cortical areas)
gaze control systems
- saccadic
- smooth pursuit
- vestibular-ocular
- vergence
- optokinetic
conjugate movements
saccadic, smooth pursuit, vestibular-ocular
disconjugate movement
vergence
saccadic
-function
rapid eye movement that brings image of object onto the fovea (jumpy)
smooth pursuit
-function
keeps a moving image centered on the fovea
vestibular-ocular
-function
holds image steady on the fovea during head movements
vergence
-function
keeps image on fovea when object is moved near
optokinetic
-function
holds images of the target steady on the retina during sustained head rotation
nystagmus quick phase
-function
directs the fovea toward the oncoming visual scene during self-rotation: resets the eyes during prolonged rotation
saccadic system: horizontal
-overview
frontal eye fields or superior colliculus –> contralateral PPRF (horizontal gaze center) –> contralateral [from original stimulus] CN VI lateral rectus + MLF –> ipsilateral [to original stimulus] CN III medial rectus
control mechanisms for horizontal saccadic system
- voluntary
- reflex
voluntary: frontal eye fields
reflex: superior colliculus
PPRF
paramedian pontine reticular formation = horizontal gaze center
CNs in horizontal saccadic system
contralateral CN VI
ipsilateral CN III
stimulation of the right frontal eye field
drives the eyes left
stimulation of the left frontal eye field
drives the eyes right
control mechanisms for vertical saccadic system
- voluntary
- reflex
voluntary: frontal eye fields
reflex: superior colliculus
riMLF
rostral interstitial nucleus of the medial longitudinal fasciculus = vertical gaze center
-near midbrain and diencephalon junction
cells for superior vertical gaze location
superior colliculus and posterior commissure
cells for inferior vertical gaze location
dorsal and medial to red nucleus
selective gaze palsy -can’t look up
- pineal tumor
- mass pressing on superior midbrain
selective gaze palsy - can’t look down
lesions near red nucleus
vertical saccadic system
-overview
frontal eye fields/superior colliculus –> riMLF –> CN IV (down) and CN III (up)
CNs of vertical saccadic system
CN VI and CN III
What contributes to reflexive saccadic eye movements?
- supplemetary and parietal eye fields
- superior colliculus
excitatory burst neurons
moves eyes towards target
tonic neurons
for the final locking on and fixing on the targets
steps of brainstem control for saccades
burst and tonic step then pause neurons
pause neurons
inhibit burst neurons so no further movements occur
locations of burst cells
horizontal: pontine paramedian reticular formation
vertical: rostral interstitial nucleus of MLF
locations of tonic cells
horizontal: nucleus prepositus hypoglossi in the pons
vertical: interstitial nucleus of Cajal in the midbrain
locations of pause cells
horizontal and vertical: omnipause cells of Raphe nuclei in the reticular formation
How do you test saccades?
request pt visually jump from one object to another
destructive lesion of frontal gaze center
transient conjugate eye deviation toward the side of the lesion, difficulty looking away from lesion
seizure activity in frontal gaze center
eyes deviate away from the firing gaze center (irritation)
stimulation of right parieto-occipital junction
eyes look to the right
smooth pursuit
-horizontal pathway
parieto-occipital junction (Brodmann’s area 19) –> pontine nuclei (pons) –> contralateral flocculonodular lobe/vestibulocerebellum –> contalateral vestibular nuclei –> ipsilateral CN VI –> MLF –> CN III
smooth pursuit
-vertical pathway
parieto-occipital junction (Brodmann’s area 19) –> pontine nuclei (pons) –> contralateral flocculonodular lobe/vestibulocerebellum –> contalateral vestibular nuclei –> CN III or CN IV
CNs for smooth pursuit
horizontal: CN VI and III
vertical: CN III and IV
left hemisphere firing during smooth pursuit
eyes move to the left
optokinetic pathway
smooth pursuit pathway and nuclei of the accessory optic system
for the optokinetic pathway, visual target is broken when the target reaches
the limit of the visual field
optokinetic nystagmus
eyes make a quick move in the opposite direction
What does the optokinetic pathway require to be intact?
parietooccipital eye field
How is smooth pursuit tested?
patient visually tracks slow moving object
How is otokinetic tested?
optokinetic tape - move tape through fingers in front of the patient
-expect to see optokinetic nystagmus
lesion of the parietal lobe
causes loss of smooth pursuit movements toward the side of the lesion. No OKN when tape is moved toward the damaged lobe.
vestibular-ocular system
-head turned right
-actiavtes right labyrinth –> CN VIII –> vestibular nuclei –> left CN VI –> MLF –> right CN III
testing vestibular-ocular system
Doll’s eye maneuver - eyes move in opposite direction of head turning
Ice water caloric - eye deviation toward irrigated ear with quick jerk (nystagmus) back. must be conscious to have the corrective jerk or nystagmus (COWS)
comatose pt with dysfunction at level of the brainstem testing for vestibular-ocular movement
Doll’s eyes and ice water calorics will be absent
internuclear opthalmoplegia (INO)
- impaired horizontal eye movements (lesion in the MLF of pons or midbrain)
- weak adduction of the affected eye
- abduction nystagmus of the contralateral eye
- convergence normal
left CN VI nucleus lesion
- can look right
- can’t look left with either eye
- convergence normal
left CN VI nerve palsy
- can look right
- can’t look left with left eye, but can look left with right eye
- no right eye nystagmus
- convergence normal
3 steps to near vision
convergence - so image is on fovea
accommodation - lens thickens so image is focused on fovea
pupillary constriction - better optical performance
vergence pathway
primary visual cortex –> visual association cortex –> superior colliculus/pretectal plate/both –> oculomotor N and Edinger-Westphal for dilation
test for vergence
patient focuses on a near object
Argyll-Robertson pupil (neurosyphilis)
absent light reflex but pupil constricts in near reflex testing
