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