Control of Eye Movements Flashcards
What are the important players in terms of controlling eye position?
MLF (medial longitudinal fasciculus, reflexes and cerebral centers)
What is saccadic movement? How about smooth pursuit?
Chopped up focus/rapid eye movements trying to focus an image on the fovea (scanning the room)
Smooth pursuit keeps a moving image centered on the fovea when head isn’t moving
What is vestibulo-ocular eye movement? How about vergence?
Holds image steady on fovea while head is moving
Keeps image steady on fovea when trying to see near and far
What is optokinetic eye movement?
keep image on retina while following a target
What are the major players involved in saccadic movement?
Frontal eye field (voluntary) and superior colliculus (reflexive)
What is the relay center for horizontal saccades and which part of the brainstem is it located? Which CNs are important for this?
What about vertical saccades?
Contralateral paramedian pontine reticular formation (PPRF/horizontal gaze center) in pons. CN III and VI
Rostral interstitial nucleus of the MLF (riMLF)/vertical gaze center in midbrain. CN IV and VI
Draw the pathway for horizontal saccades
Ok
Which frontal eye field and PPRF are active when eyes are turning left?
Lesion in the PPRF results in?
Right frontal eye field and left PPRF (and vice versa)
Both eyes cannot look to the side of the lesion
What happens when you have a pineal tumor?
Compression of the superior colliculus and posterior commissure = problems with vertical saccades
Damage to the nucleus of Cajal and red nucleus results in?
Problems with downward saccades since the circuit passes through this general area (medial midbrain)
What are the major players involved for reflexive saccades?
Supplementary and parietal eye fields and superior colliculus
Explain the mechanism for enabling saccadic control
Excitatory burst that moves eye towards the target > tonic neuron firing which locks the target on the fovea > pause neurons to hold the image still
What are the burst, tonic and pause cells for horizontal saccades?
Burst: PPRF
Tonic: Nucleus prepositus hypoglossi
Pause: omnipause cells of Raphe nuclei
What are the burst, tonic and pause cells for vertical saccades?
Burst: riMLF
Tonic: Interstitial nucleus of Cajal
Pause: Omnipause cells of raphe nuclei
How do you test saccadic movement?
Visually jump from one object to another
Saccades:
Destructive lesion to the frontal gaze center means?
Seizure (irritating) activity to the frontal gaze center means?
Eyes are deviated toward the lesioned eye field (that guy whose eyes are stuck to the left)
Eyes are deviated away from the lesioned eye field
What are the major players of the smooth pursuit pathway?
Parieto-occipital junction (area 19)
Vestibulocerebellum
Medial vestibular nuclei
MLF
Draw the smooth pursuit pathway
Ok
Smooth pursuit: If we are moving eyes left, which hemisphere is stimulated?
Left hemisphere (and vice versa)
Draw the optokinetic pathway
Ok
How would you test smooth pursuit movements?
Visually track slow moving object (using optokinetic tape) and see optokinetic nystagmus
When is optokinetic movement lost?
Lesions of parietal lobe equals loss of smooth pursuit towards side of lesion. No Optokinetic nystagmus when tape is moved towards side of damaged lobe
Draw the vestibulo-occular reflex pathway again
OK
How do you test vestibulo-ocular movements?
When are these tests absent?
Doll’s eye maneuver and ice water caloric
These will be absent in patient with brainstem level lesion
What are doll’s eye maneuver and ice water caloric tests?
Doll’s eye - eyes move in opposite direction of head turning
Ice water caloric - nystagmus to irrigated ear
Internuclear Ophtalmoplegia (INO)
Cause
Clinical
- MLF lesion (ipsilateral to eye that cannot abduct)
- Weak adduction in affected eye and abduction nystagmus of contralateral eye
Draw out the differences between INO (MLF lesion), CN VI nucleus lesion and CN VI palsy
Ok
Compare and contrast INO, CN VI nucleus lesion and CN VI palsy
INO: affected eye cannot adduct, other eye has nystagmus
CN VI nucleus: both eyes cannot move to the side of lesion from central position
CN VI palsy: cannot laterally move affected eye
What is needed to have the near reflex?
Convegence so image is on fovea (MLF is bypassed)
Pupillary constriction for better optical performance
Accommodation to thicken lens so image is focused on fovea
Describe the pathway of the Near reflex
Normal visual pathway > visual association cortex > superior colliculus, pretectal area or both > CN III (adduction of MR) and EWN (pupillary constriction)
How would you test vergence?
Make patient focus on a near object and you should see vergence
Argyll Robertson pupil
Absent light reflex, but pupil constricts during near reflex testing
Associated wit heurosyphilis
