Primary Motor Pathway

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Hilary Merritt
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1 Understanding Eye Movements Abdullah Moh. El-Menaisy, MD, FRCS Chief, Neuro-ophthalmology ophthalmology & Investigation Units, Dhahran Eye Specialist Hospital, Dhahran, Saudi Arabia Primary Motor Pathway UMN Cerebral Cortex Spinal Cord LMN Muscle 1

& Investigation Units, Dhahran Eye Specialist Hospital,

2 Ocular Motor Pathway Supranuclear Cerebral Cortex Internuclear Connections Brain Stem Infranuclear Muscle The control of eye movements is mediated through multiple neural circuits interconnect cortex, basal ganglia, vestibular nuclei, cerebellum & ocular motor nuclei in the brain stem. The ocular motor system consists of supranuclear, internuclear & nuclear components. 2

interconnect cortex, basal ganglia, vestibular nuclei, cerebellum & ocular motor nuclei in

3 1. Supranuclear: descending fibers from cerebral hemispheres to brain stem (frontal eye fields) 2. Internuclear: interconnections between nuclei (MLF) 3. Nuclear: nuclei of 3 rd, 4 th and 6 th cranial nerves The ocular motor system has one purpose to place & maintain the images of regard on the fovea. The task becomes more complex when the objects, the head or both are moving. 3

Nuclear: nuclei of 3 rd, 4 th and 6 th cranial nerves The ocular motor system has one purpose

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5 Functional Classification of Eye Movement Systems Direct the fovea to an object of interest: Saccades Smooth pursuit Vergence Hold images steady on the retina: Fixation Vestibulo-ocular reflex (VOR) Optokinetic nystagmus From: Anges M.F. Wong, Eye Movement Disorders, Oxford University Press,2008 5

the retina: Fixation Vestibulo-ocular reflex (VOR) Optokinetic nystagmus

6 Bring images rapidly onto the fovea. Saccades Velocity: / sec. Intentional, reflexive & spontaneous types. The frontal eye field controls saccades to the contralateral direction. Pursuit Holds the image of a moving target on the fovea. Velocity: up to 100 / sec. Parieto-occipito-temporal temporal region controls pursuit in the epsilateral direction. 6

The frontal eye field controls saccades to the contralateral direction.

7 Vergence Eye Movements Maintain fusion of images when targets move towards or away from the eyes. Velocity: 20 / sec. Control center lies in the midbrain. Vestibulo-ocular ocular Reflex (VOR) Maintains fixation during brief head movements. Input from vestibular nuclei travels through MLF to ocular motor nuclei. Checked by oculo-cephalic cephalic maneuver, caloric testing or rotating chair. 7

Vestibulo-ocular ocular Reflex (VOR) Maintains fixation during brief head movements.

8 Optokinetic Nystagmus (OKN) Maintains fixation during target movement or sustained head movements. Fast & slow phases. Fast phase is controlled by contralateral frontal eye field & slow phase by ipsilateral parieto-occipito occipito- temporal area. Role of Cerebellum Controls smoothness of pursuit movements & accuracy of saccades. Maintenance of eccentric gaze. 8

Fast phase is controlled by contralateral frontal eye field & slow phase by ipsilateral

9 Neural Integrator Eye movement is affected by the properties of the eyeball, suspensory ligaments and orbital fascia Eccentric gaze holding is the function of neural integrator Inputs from the nucleus prepositus hypoglossi and the medial vestibular nuclei to the abducens nucleus Horizontal Gaze Neuro-anatomy (Saccades) 9

of neural integrator Inputs from the nucleus prepositus hypoglossi and the

10 Horizontal Gaze Neuro-anatomy (Pursuit) Vertical Gaze Neuro-anatomy 10

11 Approach Clinical picture: Double vision ( 3 rd,4 th, 6 th N palsy or vergence disorders) Blurring of vision, dizziness (conjugate movement disorders) Neurological deficit Examination: Inspection Approach Pursuit movements Cover test Saccadic movements Optokinetic nystagmus Vestibulo-ocular ocular reflex Fundus Directed neurological examination 11

deficit Examination: Inspection Approach Pursuit movements Cover test Saccadic

12 Examination Inspection: Pursuit Movements: Examination 12

13 Examination Cover Test: Saccadic Movements: Examination 13

14 Examination Optokinetic Nystagmus: Examination Vestibulo-ocular ocular Reflex: 14

15 Approach Localization: Horizontal gaze palsy: lesions) Vertical gaze palsy: (cerebral cortex or pontine (midbrain lesions) Gaze palsy with intact VOR: lesions) 3 rd, 4 th, 6 th nerve palsy (supranuclear (nuclear or infranuclear lesion) 1. Myasthenia gravis 2. Myopathies Differential Diagnosis 3. Orbital disease 15

lesions) 3 rd, 4 th, 6 th nerve palsy (supranuclear (nuclear or infranuclear

16 Case:1 MRI 16

17 Case: 2 Case: 3 17

18 18 MRI

19 Conclusion The main function of the ocular motor system is to place & maintain i the images of regard on the fovea. The control of eye movements is mediated through multiple neural circuits interconnect cortex, basal ganglia, vestibular nuclei, cerebellum & ocular motor nuclei in the brain stem. Although supranuclear palsy could be asymptomatic, yet ocular motor nerves palsy present with double vision & ocular misalignment Conclusion Gaze abnormalities never exist in neurological isolation. Neuro-imaging & neurological evaluation are mandatory 19

cerebellum & ocular motor nuclei in the brain stem.

20 20 Thank you

The Physiology of the Senses Lecture 11 - Eye Movements www.tutis.ca/senses/

The Physiology of the Senses Lecture 11 - Eye Movements www.tutis.ca/senses/ Contents Objectives... 2 Introduction... 2 The 5 Types of Eye Movements... 2 The eyes are rotated by 6 extraocular muscles....