Eye Movements Flashcards
High visual acuity is where?
Fovea of central retina
What is foveation?
Eye movements to direct fovea to objects of interest or to compensate for disturbances that cause fovea to be displaced from target already being foveated
How is foveation achieved or maintained?
Via shift for new targets
Stabilization for moving targets
What is saccades?
Rapid, ballistic movements that abruptly change the direction of fixation
Vision is transiently suppressed during saccades
Occur reflexively whenever eyes are open
What does ballistic mean in reference to saccades?
Saccade generating system does not respond to subsequent changes in the position of the target during the course off the eye movement
If target moves during time, saccade will miss the target and a second saccade must be made to correct the error
What is smooth pursuit?
Slower tracking movements designed to keep moving stimulus on the fovea once foveation is achieved
Voluntary control in that the observer can choose whether or not to track a moving stimulus
What is vergence?
Align the fovea of each eye with targets located at different distances from the observer
What is vestibulo-ocular reflex?
Stabilize gaze relative to the external world compensating for head movements
VOR is senstive to?
Insensitive to slow movements (below 1 Hz) or to persistent rotation of the head
Visual input cues the opto-kinetic system to compensate for these.
Three antagonist pairs of muscles for eye movement?
1) Lateral and medial rectus muscles
2) Superior and Inferior rectus muscles
3) Superior and Inferior oblique muscles
Functional movements of eye muscles?
Horizontal - adduction/abduction - lateral/medial rectus
Vertical - elevation/depression - superior/inferior rectus
Torsional - intorsion/extorsion - superior/inferior oblique
What is intorsion/extorsion?
Intorsion - top of eye towards nose
Extorsion - top of eye away from nose
Horizontal eye movement control?
Lateral rectus - abduction
Medial rectus - adduction
Vertical control of eye movement?
Superior/inferior rectus and oblique
Relative contribution depends on horizontal location of eye
Vertical control of abducted eye?
Superior and inferior rectus muscles
Vertical control of adducted eye?
Superior and inferior oblique muscles
Torsional control of eye?
Superior oblique - intorsion
Inferior oblique - extorsion
Lower MN of extraocular muscles?
CN III, IV, VI
What muscles of the eye are innervated by what?
Abducens - ipsilateral lateral rectus
Trochlear - contralateral superior oblibue
Occulomotor - the rest
Describe occulomotor innervation
Each muscle has its own separate group of lower MN within the nuclear complex of CN III
Separate group also innervates the levator muscle of the eyelid
Para pre fibers for pupillary constriction
Direction and amplitude of saccades is controlled by?
duration of neural activity in the lower MN of the CN nuclei and direction is determined by which eye muscles are activated.
Eye muscle nuclei are controlled by?
Gaze centers in the reticular formation
Describe teh paramedian pontine reticular formation
In the pons and controls the horizontal movement of eyes
What reticular formations control what?
Paramedian pontine reticular formation - horizontal
Rostral interstitial nucleus (rostral midbrain) - vertical
Both gaze centers for oblique movements
Describe internuclear opthalmoplegia
Lesion to MLF disrupts he oculomotor n.
Eye ipsilateral to lesion does ont adduct
Nystagmus of the contralateral lesion eye
Side of internuclear ophthalmoplegia?
The side of the INO is the side of the lesioned MLF
Side of INO is the side where eye adduction is weak
Convergence in a internuclear opthalmoplegia?
Spared because the oculomotor inputs for their control oringiate in the pretectal region (not in the MLF)
Internuclear ophtalmoplegia is associated with?
MS, pontine infarcts, or neoplasms
What is the frontal eye field?
Located in the premotor region to work in conjuction with braistem areas to coordinate movements
Function of FEF?
Each FEF generates both horizontal and vertical saccades in the contralateral direction
R FEF deviates to teh left
L FEF deviates to the right
Guided by sensory stimuli
When FEF is damaged what happens?
The other FEF acts unopposed and eyes deviate toward the lesion (wrong-way eyes)
What FEF is hyperstimulated what happens?
Eyes are deviated away from the seizure focus
Saccades and smooth pursuit movements controlled by?
Similar structures like PPFR, superior colliculus, FEF.
Parietal and occipital lobes also receive visual from dorsal spatial visual stream and is essential for initiation
Activation of caudate nuclues or s. nigra in the pars reticulata leads to for eyes?
Disinhibit neurons in the superior colliculus facilitating the initiation and termination of eye movements.
Pontine and cerebellum contributions to eye movements
Pontine nuclei receive input from frontal, parietal and occipital cortical areas and projects to cerebellar vermis
Cerebellum modulates accuracy of eye movements by adjusting gain to the velocity of movement of targt.
Done in part via connections to gaze centers in the reticular formation
Also a direct connection from vestibular nuclei to the vestibulo-cerebellum for VOR
