Eye movements Domina Petric, MD

Eye movements adjust fixation when visual target moves adjust fixation during head movements adjust fixation when acquiring a new target

Eye muscles Abducens nucleus, abducens nerve Ipsilateral rectus lateralis muscle ABduction Trochlearis nucleus, trochlearis nerve CONTRALATERAL superior oblique muscle Downward gaze, intorsion Occulomotor nucleus, occulomotor nerve Ipsilateral inferior, superior and medial rectus muscle; inferior oblique muscle Upward gaze, ADuction, downward gaze without intorsion

Eye movements Conjugate eye movements: eyes move in the same direction Disconjugate eye movements: eyes move in opposite direction Saccades: quick, ballistic Smooth pursuit: slow, visually guided Optokinetic: smooth pursuit and saccades combination, visually guided Vestibulo-ocular: slow, vestibular guided Vergence (convergence, divergence): visually guided near and far fixations

Saccades Saccade is a quick, ballistic eye movement that allows us to change fixation point from one target to another. 200 ms is necessary interval between the onset of the target and the onset of the eye movement for target fixation.

Smooth pursuit eye movements Visually guided eye movements. After catch-up saccade, eyes can track the target smoothly.

Optokinetic nystagmus Optokinetic nystagmus has two components: saccade component and smooth pursuit component. Saccade Saccade Smooth pursuit Smooth pursuit

Both eyes are in adduction. Convergence Both eyes are in adduction. Near objects fixation.

Both eyes are in abduction. Divergence Both eyes are in abduction. Far objects fixation.

PPRF PPRF is Paramedian Pontine Reticular Formation and it is horizontal gaze center. PPRF controls horizontal movements of the eyes. When we look at the right, right PPRF sends excitatory signals to the right abducens nucleus so the right lateral rectus muscle is activated. Internuclear neuron that crosses the midline, sends excitatory impulse to the contralateral (in this case left) oculomotor nucleus: activation of the left medial rectus muscle.

Vertical gaze center is located in the mesencephalon.

Upper motor neuronal control of eye movements Frontal eye field Superior colliculus in the midbrain

Upper motor neuronal control of eye movements Sensory map represents locations in the contralateral visual hemifield. Sensory map is present in both frontal eye field and superior colliculus. There is also a motor map for saccadic eye movements located in frontal eye field and superior colliculus.

Frontal eye field (Brodmann´s area 8) Frontal eye field is connected with ipsilateral superior colliculus and with contralateral gaze centers of the reticular formation (horizontal and vertical gaze centers). Lesion in the frontal eye field or in the superior colliculus causes deficit in saccadic eye movements. Frontal eye fields are concerned with intentional saccades to the opposite (contralateral) direction. If the patient has a stroke involving the anterior parts of the premotor cortex, that patient can not intentionally look at the opposite side: if the left frontal eye field is damaged, patient can not look to the right side if asked.

Superior colliculus Superior colliculus generate express saccades that are not associated with planned movements of the eyes. If we hear a noise, we will automatically look towards the source of that noise.

Literature https://www.coursera.org/learn/medical-neuroscience/lecture: Leonard E. White, PhD, Duke University