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 CristaeMaculae

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 CristaeMaculae

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