Post on 31-Dec-2015
description
Compensatory Eye Movements
John Simpson
Functional Classification of Eye Movements
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 stabilize the eye when the head moves
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
Cupula and otoliths move sensory receptors
Cristae Maculae
Angular Position
Angular Acceleration
Angular Velocity
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 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
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