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Transcript
Compensatory Eye Movements
John Simpson
Functional Classification of Eye Movements
Movements that stabilize the eye when the head moves
Vestibulo-ocular
Uses vestibular input to hold images stable on the
retina during brief or rapid head movement
Optokinetic
Uses visual input to hold images stable on the
retina during sustained or slow head movement
Movements that keep the fovea on a visual target
Saccade
Brings new objects of interest onto the fovea
Smooth Pursuit
Holds the image of a moving target on the fovea
Vergence
Adjusts the eyes for different viewing distances
in depth
Cupula and otoliths move sensory
receptors
Cristae
Maculae
Angular
Acceleration
Angular
Velocity
Angular
Position
Cupula
Deflection
Canal afferents respond to cupula motion
Canal afferents code velocity
• Spontaneous activity
allows for bidirectional
signaling
• S-curve is common
• Different cells have
different ranges and
different dynamics
• Population code
Cupula and otoliths move sensory
receptors
Cristae
Maculae
Classes of eye movements
• Reflexive – gaze stabilization
– VOR
• Stabilize for head movements
– Optokinetic
• Stabilize for image motion
• Voluntary – gaze shifting
– Saccades
• Acquire stationary target
– Smooth pursuit
• Acquire moving target
– Vergence
• Acquire target in depth
VOR With and Without Vision
rVOR gain varies with frequency
• Almost perfect > 1Hz
• Low gain for low
frequencies (0.1Hz)
• Sensory mechanisms
can compensate
(optokinetic reflex)
Optokinetic reflex
• Optokinetic nystagmus
• Neural pathway (AOS)
convergent with VOR
Oculomotor muscles and nerves
• Oculomotor nerve (III)
– Medial rectus
– Superior/Inferior recti
– Inferior oblique
• Trochlear nerve (IV)
– Superior oblique
• Abducens nerve (VI)
– Lateral rectus
The 3-Neuron Arc
Primary Effects of Canals on Eye Muscles
Canal
Excites
Inhibits
Horizontal
Ipsi MR, Contra LR
Ipsi LR, Contra MR
Anterior
Ipsi SR, Contra IO
Ipsi IR, Contra SO
Posterior
Ipsi SO, Contra IR
Ipsi IO, Contra SR
Secondary Effects of Canals on Eye Muscles
19.3 Organization of the cranial nerve nuclei that govern eye movements.
19.7 Synaptic circuitry responsible for horizontal movements of the eyes to the right.
Translational VOR
• Compensates for change in head position
with respect to gravity
• Compensates for linear motion as
opposed to rotational motion