Control of Eye movements Flashcards
_________ are the vestibular information that normal head movements require
Vestibular information
____ ________ _____ _________ is the proprioceptive information that is involved with eye movements
eye movement and position
What is involved in selecting the visual target in a normal eye movement?
Brainstem and cortical areas
What are the three things that help to achieve the control of the eye position
medial longitudinal fasciculus
reflexes
cerebral centers
What is the main reflex that is involved in the eye movements?
The vestibuloocular reflex
List the 4 supranuclear gaze control systems
- saccadic
- smooth pursuit
- vestibular-ocular
- vergence
This gaze control system is the rapid eye movement that brings to object onto the fovea
Saccadic
This supranuclear gaze control system keeps the moving image centered on the fovea
Smooth pursuit
your eyes are moving but your head is not; H test
This gaze control system keeps the image steady on the fovea during head movements
vestibular-ocular
This gaze control system keeps an image on the fovea when the object is moved near or far away
The vergence system
Describe conjugate movements of the eye
The eyes move in the same direction
What is the function of the vestibular eye movement
holds the image steady on the fovea during brief head rotations
eyes move opposite of the head movement so that you are able to stay focused on the eye movement (conjugate)
What is the function of the smooth pursuit eye movement
holds the image of a moving target steady on the fovea
with a moving head; conjugate deviation toward the direction of movement of the object
What is the function of the saccade eye movement
brings the image of an object of interest onto the fovea
rapid conjugate deviation toward the opposite side
What is the function of the nystagmus quick phase
directs the fovea toward the oncoming visual scene during self rotation; resets the eyes during prolonged rotation
quick deviation toward the stimulated labyrinth
What is the function of the optokinetic eye movement?
Holds the image of interest steady on the retina during sustained head rotation
maintains deviation of the eyes initiated by the vestibuloocular reflex ; quick deviation toward inhibited cerebellum
What is the function of vergence
moves the eyes in opposite directions so that images of a single object are placed on both fovea
accommodation to near targets
In the saccadic system the ______ ______ _______ are voluntary and the _______ ________ are reflexive
Frontal eye fields
Superior colliculus
The ______ _______ _______ _______ is also known as the horizontal gaze center
Paramedian pontine reticular formation (PPRF)
Describe the path of the saccadic system (horizontal system)
The rapid eye movement brings the image to the fovea
The frontal eye fields receive this info and it is sent to the PPRF on the contralateral side
These fibers project to CN VI and then to CN III via the medial longitudinal fasciculus and to the eye muscles that will allow the eyes to look left or right
If the left PPRF is damaged, then the patient will not be able to look to the _______ for a saccade movement
left
Where are the frontal eye fields located?
middle frontal gyrus
If the right frontal eye fields are stimulated, the patient will look ______
left
Describe the path of the saccadic system (vertical)
Rapid eye movement brings the image of the object on to the fovea
The frontal fields get this information and it is sent to the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) in the MIDBRAIN
This then travels to the CN IV and the CN III nuclei and causes the eye muscles to look up (conjugate)
Where is the PPRF located?
In the pons
Where is the riMRF located?
in the rostral midbrain near the superior fasciculus and posterior commissure
If there is an enlargement of the pineal gland, what will occur to the field of vision?
If the gland is large enough to compress on the posterior commissure, then there will be a vertical saccades issue
If there is a lesion, or a blood supply issue to the area that encompasses the red nucleus, interstitial nucleus of Canal, and the oculomotor nucleus, what will happen clinically?
The patient will not be able to look down
What are some of the things that help to contribute to the reflex saccadic eye movements?
Supplementary and parietal eye movements and the superior colliculus
Describe in detail the various neurons that are needed throughout the control of saccadic movements
- burst
- tonic
- pause
- needs to be a pulse of neuronal firing in order to move the eyes to the target (burst)
- The tonic neurons help to lock onto the target
- The pause neurons help to inhibit the burst neurons so that no more movements happens and the target can be looked at
Where are all of the cells of the horizontal saccadic movements located?
pons
Where are all of the cells of the vertical saccadic movements located?
midbrain
Differentiate between the burst cells in the horizontal and the vertical pathways of the saccadic movements
Horizontal are located in the pontine paramedic reticular formation
Vertical are located in the rostral interstitial nucleus of MLF (riMLF)
Differentiate between the tonic cells in the horizontal and the vertical pathways of the saccadic movements
Horizontal: nucleus prepositus hypoglossi
Vertical: interstitial nucleus of Canal
Differentiate between the pause cells in the horizontal and the vertical pathways of the saccadic movements
Both are in the omnipause cells of the Raphe nuclei
How do you test the saccadic movements clinically?
Do something that makes the patient jump from one image to another
Have the patient move their eyes to your fingers that are wiggling in the periphery of their vision
If there is a destructive lesion in the frontal gaze center, what happens?
eye deviation is towards the lesion
like a stroke
If there is an irritation lesion (seizure) in the frontal gaze center, what happens?
The eye deviation is away from the firing gaze center
Describe the pathway of smooth pursuit
Occurs in the parietooccipital junction
Information travels from the pontine nuclei to the vestibulocerebellum to the medial vestibular nuclei to the respective Cn nuclei
If the smooth pursuit movement is horizontal, what CN nuclei will be involved?
6 and 3
If the smooth pursuit movement is vertical, what CN nuclei will be involved?
3 and 4
If the left hemisphere is activated the eyes move to the ______ in smooth pursuit
left
Describe the pathway of the optokinetic movement
Information follows the same general pathway of the smooth pursuit movements
The visual field travels to the nucleus reticularis of the pons and the nuclei of the accessory optic system of the optic tract, and to the vestibulocerebellum, vestibular nuclei and to the nuclei of CN III, IV, and VI
What is required in order for the optokinetic movements to be intact?
parietooccipital eye field
How do you test smooth pursuit movements clinically?
Patient visually tracks slow moving objects
optokinetic tape
Lesion of the parietal lobe will cause a loss of the smooth pursuit movements (TOWARD/AWAY FROM) the lesion
TOWARDS!
Describe the vestibular-ocular system pathways
The head is turned to a side, which activates the labyrinth that is locates on that side via the semicircular ducts
The information then travels via CN VIII to the vestibular nuclei to (horizontal-3 and 6) and (vertical- 3 and 4)
If you turn your head to the right, what way will your eyes move? Which semicircular canals are activated?
Your eyes will move to the left to try to offset the movement
the right semicircular canals will be activated
What are two ways that you can test the vestibular ocular movements?
- Doll’s eye maneuver
2. Ice water caloric test
What will be true of the vestibule-occular movements that are present in a comatose patient?
They will be absent; both the dolls eyes and the ice water calorics
This is characterized by impaired horizontal eye movements as a result from a lesion int he medial longitudinal fasciculus
internuclear ophthalmoplegia
What are the impaired eye movements that are seen in internuclear ophthalmoplegia?
weak adduction of the affected eye
abduction nystagmus of the contralateral eye
In what chronic disease is a lesion in the MLF common?
MS
Where is the MLF?
In the pons and the midbrain
If the patients left eye is not able to adduct and the right has a nystagmus characteristic with abduction, what is suspected?
A lesion of the left MLF
If the patient is not able to look left, what is the suspected lesion?
A lesion in the left nucleus of CN VI
If the patient is not able to abduct their left eye, what is the suspected lesion?
A left CN VI nerve palsy that is inhibiting the left lateral rectus
What are the three components that make up the near reflex?
- convergence- image is on the fovea
- accommodation- lens thickens so that the image is on the fovea
- pupillary constriction- better optical performance (pupils narrow)
What is the pathway of the Near reflex?
- Normal visual pathway tot he striate cortex
- Visual association cortex
- Information goes to the superior colliculus or the pretectal area or both
- travels to the oculomotor nucleus, which stimulates the medial rectus motor neurons and the pre-ganglionic parasympathetic neurons of the edinger westphal nucleus
How do you test vergence clinically?
patient focuses on a near object
If a patient has a pupil that constricts in near reflex testing but does not constrict via the light reflex, what is the diagnosis?
An Argyll-Robertson pupil that is seen with neurosyphilis
