Control of Eye Movements Flashcards
Saccadic
Rapid eye movement that brings image of object onto the fovea
Smooth pursuit
Keeps a moving image centered on the fovea
Vestibular-ocular gaze control
Holds image steady on the fovea during head movements
Controlled by visual pathway and parietooccipital cortex, as well as vestibulocerebellum
Vergence
Keeps image on fovea when object is moved near or far away
Deconjugate eye movement- eyes both adduct/abduct
Eye movement systems- normal eye movements require
Head movements- vestibular info
Visual objects- vision
Eye movement and position- proprioceptive info
Selection of a visual target- superior colliculus and cortical areas
Medial longitudinal fasciculus MLF also important
Optokinetic
Holds images of the target steady on the retina during sustained head rotation- eyes and head moving
Saccadic system: Horizontal movement
Frontal eye fields (voluntary movement)- Project fibers to contralateral paramedian pontine reticular formation PPRF (horizontal gaze center), from there projects to CN VI, and then a branch passes through MLF to CN III nucleus Superior colliculus (reflexive movement)
If right frontal eye fields are stimulated, you will look
Left
PPRF lesion (left side)
Unable to look left
Saccadic system: Vertical movement
Frontal eye fields project fibers to rostral interstitial nucleus of MLF (miMLF- vertical gaze center), then projects fibers to CN III and IV for upward/downward motion
Pineal gland tumor
Will push down near superior colliculus near posterior commissure of brain and give you trouble with vertical saccads
Damage to red nucleus near interstitial nucleus of cajal in midbrain
Will have trouble with vertical saccads only when looking downwards
Neurons involved in saccadic movement
Burst neuron to get eye there
Tonic neuron to slow down and lock on
Pause neuron to stop on object
Location of neurons for horizontal/vertical saccadic movement
Horizontal all located in pons
Vertical all located in midbrain
Destructive lesion of frontal eye fields
Transient conjugate eye deviation toward the side of the lesion, difficulty looking away from lesion
Seizure/irritating activity in frontal eye field area
Eyes deviating away from the firing gaze center
Look away from irritating, look toward destruction
Horizontal and vertical smooth pursuit pathway
Parieto-occipital junction (Brodmanns 19) project fibers to pontine nuclei, then to vestibulocerebellum, then to vestibular nuclei, and then to CN VI and a branch through MLF to CN III
Vertical- same pathway but projects to CN III and IV
If left hemisphere is stimulated, eyes move to the left
Optokinetic pathway
Fibers project from visual association cortex, to nucleus of optic tract, then to the pons, then vestibulocerebellum, then vestibular nuclei, then to nuclei of whatever CN you are using
Lesion of parietal lobe
Loss of smooth pursuit movement toward the side of the lesion
No optokinetic nystagmus is seen when tape is move towards the affected lob
(optokinetic tape is the tape with a bunch of different shapes
Internuclear ophthalmoplegia
Characterized by impaired horizontal eye movements
Results from lesion in MLF in pons/midbrain (seen in MS patients)
-weak adduction of affected eye
-abduction nystagmus (nystagmus when you try to abduct) of the contralateral eye
BL MLF lesion patient trying to look left: cannot abduct left eye without nystagmus, cannot adduct right eye
-patient is able to cross eyes- adduct both at same time
Left CN VI lesion
Left eye cant abduct
Right eye cant adduct
(Im guessing because when you look left, the CN VI nucleus also sends fibers to the contralateral CN III nucleus to activate the adductor muscle of that eye, and since the CN VI nucleus is damaged, that doesn’t happen)
CN VI nerve palsy
Unable to look left on that side
Near reflex pathway (looking cross eyed)
Eyes (visual sight)- Travels through optic nerve to LGN
Fibers leave as optic radiations and travel to primary visual cortex
Travels either to superior colliculus/pre-tectal area (they don’t know which one)
Then travels to CN III nucleus and Edinger-Westphal
Because we bypassed the MLF, you can still use this pathway to adduct both eyes even if you have internuclear ophthalmoplegia
Vergence test/pathology
Patient focuses on a near object, near reflex occurs
Argyll-Robertson pupil (caused by neurosyphilis) - absent pupillary light reflex, but pupil constricts in near reflex testing
