Neural Control of Eye Movements

self motion, object motion, explore space & shift attention (stabilization, foveal gaze lock, foveal gaze shift)

what are the 3 fundamental visual sensory-motor tasks?

self motion (stabilization)

• one of the fundamental visual sensory-motor tasks

• keeps the visual field stable while we move

object motion (foveal gaze lock)

• one of the fundamental visual sensory-motor tasks

• eye movements improve visual resolution of objects by maintaining alignment of the 2 foveas with stationary & moving targets

explore space & shift attention (foveal gaze shift)

• one of the fundamental visual sensory-motor tasks

• rapid eye movements place corresponding images on the 2 foveas as we shift gaze between targets lying in different directions & distances of gaze

Donder’s law

says that torsional eye movements are highly predictable & reproducible from person to person; there is a brainstem function that systematically determines the torsional component in different gaze directions regardless of the starting gaze position; torsional movements are independent of path taken

Listing’s law

quantifies the amount of ocular torsion made in eye movements

Brown’s syndrome

• etiology: mechanical restriction of the superior oblique tendon/trochlea complex

• limited elevation of the eye when adducted

• pt might present with a head tilt to limit their diplopia

• test with the forced duction test

• appears to be an inferior oblique problem

isovergence circle

describes the locus of points that stimulate the same vergence angle in all directions of gaze

isoversion lines

describe the locus of points made that stimulate the same version angle over a range of viewing distances in a common direction of gaze relative to the head

feedback

• closed loop

• used to maintain a fixed position or slow movements of the eyes when there is adequate time to process the error signal

• 50-100ms

pursuits, fixation, OKN, vergence

what eye movements utilize feedback?

saccades, VOR

what eye movements utilize feed forward?

Hering’s law

says that there is equal innervation of yoked muscle pairs

feed forward

• open loop

• motor responses that utilize this can respond to non-visual stimuli or they respond to advanced visual info with short latencies & brief durations

• accuracy is evaluated post-movement

• 14ms

supranuclear

• top of the hierarchy of motor control

• motor planning stage

• send instructions to premotor neurons

• SC, SN, cerebellum, FEF, SEF, MT, MST, LIP

internuclear/intranuclear

• connection between nuclear & premotor sites

• MLF

premotor

• coordinates combined actions of several muscles

• execute horizontal, vertical, & torsional eye movements

• sends interneurons to nuclear level

• riMLF, PPRF

nuclear

• cranial motor nuclei making up the final common pathway

• convey information to execute slow & fast eye movements

peripheral

• cranial nerves & muscles

• 3 pairs of EOMs that rotate each eye around its center of rotation

supranuclear, internuclear, premotor, nuclear, peripheral

list the hierarchy of oculomotor control

abducens nucleus

innervates ipsilateral lateral rectus muscle

hering’s interneuron

premotor interneuron from the abducens nucleus up the MLF to the contralateral oculomotor nucleus & inputs onto the medial rectus of the contralateral eye; key for producing yoked eye movements

trochlear nucleus

innervates contralateral superior oblique muscle

oculomotor nucleus

innervates ipsilateral medial rectus, inferior rectus, & inferior oblique & contralateral superior rectus

Edinger-westphal nucleus

anterior portion of the oculomotor nucleus that contains motor neurons that control pupil size & accommodation

one & a half syndrome

• etiology: trauma affecting the abducens nucleus

• results in only the contralateral eye (to the lesion) being able to abduct in lateral conjugate eye movements

• convergence is entirely normal

adduction, elevation, intorsion

list the muscle movement actions of superior rectus

depression, adduction, extorsion

list the muscle movement actions of inferior rectus

extorsion, elevation, abduction

list the muscle movement actions of inferior oblique

depression, abduction, intorsion

list the muscle movement actions of superior oblique

abduction

list the muscle movement actions of lateral rectus

adduction

list the muscle movement actions of medial rectus