Compensatory%20Eye%20Movements

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Compensatory Eye Movements

• John Simpson

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Functional Classification of Eye Movements
Movements that stabilize the eye when the head
moves

• Vestibulo-ocular
• Optokinetic

• Uses vestibular input to hold images stable on
  the retina during brief or rapid head movement
• 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 Smooth Pursuit Vergence
Brings new objects of interest onto the
fovea Holds the image of a moving target on the
fovea Adjusts the eyes for different viewing
distances in depth
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Cupula and otoliths move sensory receptors
Cristae
Maculae
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Angular Acceleration
Angular Velocity
Angular Position
Cupula Deflection
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Canal afferents respond to cupula motion
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Canal afferents code velocity

• Spontaneous activity allows for bidirectional
  signaling
• S-curve is common
• Different cells have different ranges and
  different dynamics
• Population code

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Cupula and otoliths move sensory receptors
Cristae
Maculae
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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

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VOR With and Without Vision
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rVOR gain varies with frequency

• Almost perfect gt 1Hz
• Low gain for low frequencies (0.1Hz)
• Sensory mechanisms can compensate (optokinetic
  reflex)

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Optokinetic reflex

• Optokinetic nystagmus
• Neural pathway (AOS) convergent with VOR

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Oculomotor muscles and nerves

• Oculomotor nerve (III)
• Medial rectus
• Superior/Inferior recti
• Inferior oblique
• Trochlear nerve (IV)
• Superior oblique
• Abducens nerve (VI)
• Lateral rectus

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The 3-Neuron ArcPrimary 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

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Secondary Effects of Canals on Eye Muscles
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19.3 Organization of the cranial nerve nuclei
that govern eye movements.
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19.7 Synaptic circuitry responsible for
horizontal movements of the eyes to the right.
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Translational VOR

• Compensates for change in head position with
  respect to gravity
• Compensates for linear motion as opposed to
  rotational motion