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Understanding Eye Movements Abdullah Moh. ElEl-Menaisy, MD, FRCS Chief, Neuro Neuro--ophthalmology & Investigation Units, Dhahran Eye Specialist Hospital, Dhahran, Saudi Arabia Primary Motor Pathway Cerebral C Cortex UMN Spinal Cord LMN Muscle 1 Ocular Motor Pathway Cerebral Cortex Supranuclear 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 supranuclear,, internuclear & nuclear components. 2 1. Supranuclear: descending fibers from cerebral hemispheres to brain stem (frontal eye fields) 2. Internuclear: interconnections between nuclei Internuclear: (MLF) 3. Nuclear: nuclei of 3rd, 4th and 6th 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 4 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 Fi ti • Vestibulo-ocular reflex (VOR) • Optokinetic nystagmus From: Anges M.F. Wong, Eye Movement Disorders, Oxford University Press,2008 5 Saccades ■ Bring images rapidly onto the fovea fovea. ■ Velocity: 300 – 700 700°° / 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 fovea. ■ Velocity: up to 100 100°° / sec. ■ ParietoParieto-occipito occipito--temporal region controls pursuit in the epsilateral direction direction. 6 Vergence Eye Movements ■ Maintain fusion of images when targets move towards or away from the eyes. ■ Velocity: 20 20°° / sec. ■ Control center lies in the midbrain midbrain. Vestibulo--ocular Reflex (VOR) Vestibulo ■ Maintains fixation during brief head movements. movements ■ Input from vestibular nuclei travels through MLF to ocular motor nuclei. ■ Checked by oculooculo-cephalic maneuver, caloric testing or rotating chair. 7 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 parietoparieto-occipito occipito-temporal area. Role of Cerebellum ■ Controls smoothness of pursuit movements & accuracy of saccades. ■ Maintenance of eccentric gaze. 8 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 Horizontal Gaze Neuro-anatomy (Pursuit) Vertical Gaze Neuro-anatomy 10 Approach Clinical picture: ■ Double vision ( 3rd,4th, 6th N palsy or vergence disorders) ■ Blurring of vision, dizziness (conjugate movement disorders) ■ Neurological deficit Approach Examination: 11 ■ Inspection ■ Pursuit movements ■ Cover test ■ Saccadic movements ■ Optokinetic nystagmus ■ Vestibulo--ocular reflex Vestibulo ■ Fundus ■ Directed neurological examination Examination Inspection: Examination Pursuit Movements: 12 Examination Cover Test: Examination Saccadic Movements: 13 Examination Optokinetic Nystagmus: Examination Vestibulo--ocular Reflex: Vestibulo 14 Approach Localization: ■ Horizontal gaze palsy: lesions) ■ Vertical gaze palsy: (cerebral cortex or pontine (midbrain lesions) ■ Gaze palsy with intact VOR: lesions) ■ 3rd, 4th, 6th nerve palsy (supranuclear (nuclear or infranuclear lesion) Differential Diagnosis 15 1. Myasthenia gravis 2. Myopathies 3. Orbital disease Case:1 Case: 1 MRI 16 Case: 2 Case: 3 17 MRI 18 Conclusion ■ The main function of the ocular motor system is to place & maintain i t i th the iimages off regard d on th the ffovea. ■ 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. ■ NeuroNeuro-imaging & neurological evaluation are mandatory 19 Thank you 20