eye_movements - Eye Movements Eye Movements Donna L. Hill,...

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Unformatted text preview: Eye Movements Eye Movements Donna L. Hill, MD Neuro­ophthalmology Departments of Neurology and Ophthalmology UF&Shands Jacksonville Normal Eye Movements Normal Eye Movements • • • • • • Objective: Foveation Extraocular muscles Muscle innervation – CNs III, IV, and VI Cranial nerve nuclei Three primary types of movements Pathologic eye movements Objective: foveation Objective: foveation • fovea – most sensitive portion of retina • we need to orient, either voluntarily or we reflexively, to important stimuli reflexively, • accomplished by directing our eyes to a accomplished target so that it is projected onto the fovea target • to maintain foveation, we depend on visual to feedback as the primary source of feedback information on eye movement accuracy information Extraocular muscles Extraocular muscles • Superior rectus – moves eye up • Inferior rectus – moves eye down left • Medial rectus – moves eye in (a­d­duction) • Lateral rectus – moves eye out (a­b­duction) • Inferior oblique – moves eye up when it is in an adducted position; also extorts the eye. • Superior oblique – moves eye down when it is adducted; also intorts the eye. Isolating Extraocular Muscles Isolating Extraocular Muscles CN III CN III CN III CN III • Superior division ­ Superior rectus muscle ­ Levator palpebrae superioris muscle • Inferior division ­ Medial rectus muscle ­ Inferior rectus muscle ­ Inferior oblique muscle ­ Parasympathetic innervation to pupil CN IV CN IV CN VI CN VI CN VI Coordination of Eye Movements Coordination of Eye Movements • Separate systems exist to control each different subtype of eye movement: saccades, smooth pursuit, and vergence • May be nuclear or supranuclear control • May be reflexive or voluntary • Separate systems exist to govern vertical and horizontal eye movements Targeting Eye Movements Targeting Eye Movements 1. Saccades: Quick, darting conjugate movements which direct the eyes to a new target. 2. Smooth pursuit: A slower conjugate movement which allows for tracking of a moving object, or of a stationary object while we are moving. 3. Convergence: A dysconjugate movement of both eyes toward the midline to allow for focusing on a near object by adjusting the angle Variety of pathways contribute to saccadic Variety of pathways contribute to saccadic control and smooth pursuit Saccades Saccades • Under the control of three different areas in the brain: – voluntary saccades ­ frontal eye fields (Brodmann’s area 8) – reflexive saccades to complex stimuli ­ parietal lobes (Brodmann’s area 7) – reflexive saccades to elementary stimuli ­ superior colliculi Voluntary Saccades (horizontal) Voluntary Saccades ( results in saccade to contralateral space Voluntary Horizontal Saccades FEF FEF CEREBRAL HEMISPHERE III MIDBRAIN III PONS VI VI PPRF PPRF Yoking Mechanism LR MR MR III LR MIDBRAIN III PONS VI VI Reflexive Saccades Reflexive Saccades ­ to complex stimuli originates in area 7 of the parietal lobe ­ to elementary stimuli originates in superior colliculi dorsolateral prefrontal cortex involved in planning of eye mvts Smooth Pursuit Smooth Pursuit Two types: 1. Voluntary (actually termed “smooth pursuit”) movements ­ originate in the temporo­ parietal lobe 2. Reflexive ­ which are under vestibular nuclear control alone and constitute what is called the vestibulo­ocular reflex (VOR). Voluntary Voluntary Smooth Pursuit • originates near the angular gyrus ­ Area 39 at the temporal parietal occipital junction • cells in this region are able to compute the speed and direction of a moving object • results in ipsilateral smooth pursuit IPSI Optokinetic Reflex Optokinetic Reflex • Combination of saccades and smooth pursuit that allow tracking of targets in turn (e.g. counting sheep as they jump over a fence). • smoothly pursue one target, then saccade in the opposite direction to pick up the next target • parieto­temporal junction (smooth pursuit area) projects down to ipsilateral vestibular nucleus, inhibits it allowing ipsilateral smooth pursuit • then, the FEF of the same hemisphere generates a saccade back (contralateral) to the next Reflexive Smooth Pursuit ­ VOR Reflexive Smooth Pursuit ­ VOR • maintains gaze on a target despite head movement • reflex arc – semicircular canal opposite the head turn detects motion and activates the ipsi vestibular n. which deactivates its inhibitory input on the ipsilateral VI • results in eyes turning deactivates (­) input VIII opposite to the head turn p339 Medical Neuroscience, Nadeau et al Convergence Convergence • When areas of the occipital cortex detect a discrepancy in the retinal projection from each eye and amount of blur, a signal is sent to initiate convergence. • To bring a near object into focus actually involves convergence, accomodation (lens curvature increases) and pupillary constriction. Together, these 3 movements are called the near triad. Pathologic eye movements Pathologic eye movements • Muscle – Trauma, entrapment, inflammation, infiltrating diseases • Neuromuscular Junction – myasthenia gravis, botulism, organophosphate poisoning • Cranial nuclei or nerve Brainstem: stroke, hemorrhage, multiple sclerosis, tumor, trauma Subarachnoid space: Increased intracranial pressure, aneurysm, meningitis, sarcoidosis, autoimmune – Cavernous sinus: Tumor, sinus thrombosis, pituitary apoplexy, sphenoid sinusitis, carotid­cavernous fistula, Tolosa­Hunt syndrome – Orbit: Trauma, tumor, infection – – right cranial nerve III palsy right cranial nerve III palsy right cranial nerve VI palsy right cranial nerve VI palsy Gaze Palsy Gaze Palsy • inability to look in a particular direction (ie. neither eye can look right) • lesion in the FEF, the PPRF, or the CN VI nucleus – Lesion in the FEF – unable to look contralaterally, eyes deviate toward the lesion, can be overcome with VOR – Lesion in PPRF or CN VI nucleus – inability to look ipsilaterally with either eye Voluntary Horizontal Saccades FEF FEF CEREBRAL HEMISPHERE III MIDBRAIN III PONS VI VI PPRF PPRF Left MLF lesion – intranuclear ophthalmoplegia Left MLF lesion – intranuclear ophthalmoplegia Yoking Mechanism LR MR MR III LR MIDBRAIN III PONS VI VI Acknowlegdements • • • Dr. Tariq Bhatti and his patients for clinical images Dr. Angela McSwain, Dr. Nadeau’s text, Peter Duus ( “Topical Diagnosis in Neurology”), and Frank H. Netter (Ciba Collection of Medical Illustrations, Vol 1) Dr. Nancy Newman and Dr. Valerie Biousse, Neuro­ophthalmology Emory University ...
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