Control Of Eye Movements Flashcards
How are head movements transmitted for normal eye movements?
Via vestibular info
What selects a visual target?
Brainstem - superior colliculus
Cortical areas
What controls eye position?
MLF
Reflexes - VOR
Cerebral centers
What does supranuclear mean?
Brainstem
What are Saccades?
Rapid eye movement that brings image of object ONTO FOVEA
What do saccades use?
Frontal eye fields
Superior colliculus
Pontine Paramedian reticular formation
What are the effects of saccades?
Rapid conjugate deviation TOWARD opposite side
What does Smooth PUrsuit do?
Keeps MOVING IMAGE centered on fovea
What does smooth pursuit use to accomplish its goal?
Visual pathway
Parietooccipital cortex
Vestibulocerebellum
What is the effect of Smooth pursuit?
With respect to the parietooccipital cortex?
Conjugated deviation toward direction of movement of object
Same side to parietooccipital cortex
What is the Vestibulo-ocular system do?
Hold image stead on fovea during MOVING HEAD
What does the vestibulo-ocular system use?
Semicircular canals and vestibular nuclei
What is the effect of the vestibulo-ocular movement?
Conjugate deviation of eyes in opposite direction of head rotation
What does the optokinetic system do?
Hold images of the target steady on the RETINA during sustained HEAD ROTATION
What does the optokinetic system use?
Visual pathway
Parietooccipital cortex
Vestibulocerebellum and vestibular nuclei
(Same as smooth pursuit)
What is the effect of the optokinetic system?
Maintains deviation of eyes initiated by vestibuloocular reflex
What supranuclear gaze control system does dis-conjugate movement?
Vergence
What does the vergence system do?
Keeps image on fovea whether object is moved near or far away
What doe the vergence system use?
Unknown direct input to CN 3s; (via interneurons?)
What is the effect of Vergence?
Accommodation to near target by moving eyes in opposite directions so that images of a single object are placed on both foveas
What do the frontal eye fields do?
Voluntary saccades
What do superior colliculus do?
Reflexive saccades
What is the horizontal gaze center of the saccadic system?
Paramedian pontine reticular formation (PPRF)
What would happen if you damaged the PPRF on the left side?
Could not look left
What are the horizontal saccadic nuclei?
CN 6, CN3
Connected by MLF
With the horiz. Saccadic system, if the RIGHT frontal eye fields were stimulated at the middle frontal gyrus, what would eyes do?
Look left
What is the pathway for the Horizontal Saccadic System?
R. Frontal Eye field —> PPRF —> nucleus 6 —> MLF —> nucleus 3
What are the control mechanisms for the Horizontal Saccadic System?
Frontal eye fields
Superior COlliculus
Paramedian pontine reticular formation
Horiz. Nuclei (6 and 3, via MLF)
What are the Control mechanisms for the Vertical Saccadic system?
Frontal eye fields
Superior colliculus
Rostral interstitial Nucleus of the MLF (RiMLF)
Vertical Nuclei (3, 4)
What is the vertical gaze center in the Vertical Saccadic system?
Rostral interstitial Nucleus of the MLF (RiMLF)
What are the vertical nuclei of the vertical saccadic system?
Cn 3
Cn 4
Wher is the RiMLF ?
In rostral midbrain near Superior Colliculus and near posterior commissure
What could cause a problem with vertical saccades?
If region near RiMLF is compressed via a pineal tumor
What will cause the patient to have trouble looking down?
If region near interstitial nucleus of Cajal is compressed
How does the brainstem control saccadic movements?
3 steps
- Burst of neuronal firing
via excitatory burst neurons to MOVE eye toward targets - Tonic neuronal firing
Via tonic neurons to LOCK onto target - Pause neurons to INHIBIT BURST neurons
So no more movements
What are the burst, tonic, and pause neurons of the horizontal saccadic system?
Burst: PPRF
Tonic: Nucleus preposition hypoglossi
Pause: Omnipause cells of raphe nuclei
what are the burst, tonic and pause nuerons of the vertical saccadic system?
Burst: RiMLF
Tonic: interstitial nucleus of Cajal
Pause: Omnipause cells of raphe nuclei
What level is the horizontal gaze control center at?
Pons
PPRF
What level is the vertical gaze control center at?
Midbrain
RiMLF
With the Saccadic system, if the right hemisphere is activated, how will you look?
Look left
opposite of hemi activated
With the Smooth Pursuit system, if the right hemisphere is activated, how will you look?
Look left
Will be same as hemi activated
What are reflex saccadic eye movemnt done by?
Supeiror colliculus (and supplementary and parietal eye fields)
How do you test saccadic movements?
Ask patient to visually jump from one object to another
If the frontal gaze center has a destructive lesion to it, what happens to the eyes?
What could cause this?
Look TOWARD side of lesion
(Transient conjugate eye deviation toward side of lesion)
Stroke
What happens if there is seizure activity in the frontal gaze center?
Eye deviates AWAY from the firing gaze center
Seizure - irritating —> look AWAY
What are the control mechanisms for the Smooth Pursuit system?
Parietooccipital junction (brodmann’ s area 19)
Pons
Vestibulocerebellum
Medial vestibular nuclei
(horiz. 3 & 6, vert. 3 & 4)
How do you test the Smooth Pursuit system?
Ask pt. To track slow moving object
Optokinetic tape - move tape thru fingers in front of patients
What is the pathway for the Smooth Pursuit system?
Parietooccipital-occipital junction —>
Pontine nuclei —> Vestibulocerebellum
—> vestibular nuclei —> CN 6 —> MLF —> CN 3
(Or cn 4 and 3 for vertical smooth pursuit)
What happens to the smooth pursuit system if the partial lobe is lesioned?
Loss of smooth pursuit movements TOWARD side of lesion
No optokinetic nystagmus when tape is moved toward damaged lobe
What does the optokinetic system use?
Smooth pursuit pathway
Nuclei of accessory optic system
What is optokinetic nystagmus? (OKN)
Eye will make a quick move in the opposite direction when visual target is broken at end of visual field
What do you need for OKN to occur?
Intact parietooccipital eye field
What is the pathway for the Optokinetic system?
Area 14 —> Vis. Assoc. Center —> Nuclie of accessory optic system and nucleus of the optic tract —> POns
Pons —> vestibulocerebellum —> vestibular nuerlci —> Nuclei 3, 4, 6,
Pons —> Inferior olive —> cerebrocerebellum —> corrects movement errors
What are the control mechanisms for the vestibulo-ocular system?
Semicircular ducts
Cn 8
Vestibular nuclei
(Horiz. 6 and 3; vertical 3 and 4)
What will movement to the right of the head activate in the vestibulo-ocular system?
Right labyrinth
How will the eyes move when the head is turned right according to VO system?
Eyes will go left (think Doll’s eye)
How do you test the Vestibulo-ocular system/
Doll’s eye maneuver
Ice water caloric test
With the he ice water caloric test, how will eyes deviate?
Deviate toward irrigated ear
W/ quick corrective jerk Opposite
COld opposite, warm away
If a comatose patient has an absent doll’s eyes and ice water caloric test, what will that tell you?
Dysfunction of brainstem
What is the pathway for the vestibulo-ocular system?
Head turns —-> activates same side labyrinth —> CN 8 —> vestibular nuclei —> nucleus 6 —> MLF —> nucleus 3
What is INO characterized by?
Impaired horizontal eye movements
Weak adduction of affected eye
(L. Eye can’t look right)
Abduction nystagmus of opposite eye
What does INO result from?
Lesion of MLF in pons or midbrain
Who do we see INO in?
Pts. W/ MS
If the LEFT MLF is lesioned, what will occur?
LEFT eye wont look RIGHT
Left INO
What happens if the LEFT Abducens NUCLEUS is lesioned?
Both eyes can’t look LEFT
what happens if the LEFT CN 6 Nerve is lesioned?
LEFT eye wont look LEFT
What are the control mechanisms for Vergence?
Unknown input to CN 3 neurons, most likely thru interneurons
How do you test Vergence?
Ask pt. To focus on near object, watch for near object reflex (convergence, accomodation, pupillary constriction)
What is a pathology of the vergence system?
Argyll Robertson pupil
What can cause argyll Robertson pupil?
Neurosyphylis
How does an Argyll RObertson pupil present?
NO pupil constriction w/ LIGHT
BUT
Pupil CONSTRICTION w/ NEAR REFLEX
What are the components of the near reflex?
Accomodation
Convergence
Pupillary constriction
How can we still have convergence with INO?
Because convergence does not use MLF
What is convergence?
Eyes together so that image is on the fovea
What is accomodation?
Lens thickens - for near images
Lens thins - for distant
So that image is focused on fovea
What is the pupillary constriction for?
Better optical performance by focusing light
What are the steps in the near reflex ?
- Normal visual pathway
- Visual association area
- Superior colliculus or pretectal area
SC —> CN 3 nucleus —> both MRs to converge eyes
Pretectal area —> EW nucleus —> pupillary constriction
