Eye Movements

1. Eye Movements

2. 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

3. Objective: foveation • fovea – most sensitive portion of retina • we need to orient, either voluntarily or reflexively, to important stimuli • accomplished by directing our eyes to a target so that it is projected onto the fovea • to maintain foveation, we depend on visual feedback as the primary source of information on eye movement accuracy

4. Extraocular muscles • Superior rectus – moves eye up • Inferior rectus – moves eye down • Medial rectus – moves eye in (a-d-duction) • Lateral rectus – moves eye out (a-b-duction) • 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. left

5. Isolating Extraocular Muscles

6. CN III

7. 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

8. CN IV CN VI

9. CN VI

10. 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

11. Targeting Eye Movements • Saccades: Quick, darting conjugate movements which direct the eyes to a new target. • Smooth pursuit: A slower conjugate movement which allows for tracking of a moving object, or of a stationary object while we are moving. • Convergence: A dysconjugate movement of both eyes toward the midline to allow for focusing on a near object by adjusting the angle between the eyes.

12. Variety of pathways contribute to saccadic control and smooth pursuit

13. 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

14. Voluntary Saccades (horizontal) results in saccade to contralateral space

15. Voluntary Horizontal Saccades FEF FEF CEREBRAL HEMISPHERE III MIDBRAIN III PONS VI VI PPRF PPRF

16. LR MR MR LR III MIDBRAIN III PONS VI VI Yoking Mechanism

17. 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

18. Smooth Pursuit Two types: • Voluntary (actually termed “smooth pursuit”) movements - originate in the temporo-parietal lobe • Reflexive - which are under vestibular nuclear control alone and constitute what is called the vestibulo-ocular reflex (VOR).

19. 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

20. 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 • parieto-temporal 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 target

21. deactivates (-) input VIII 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 opposite to the head turn p339 Medical Neuroscience, Nadeau et al

22. 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.

23. 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, carotid-cavernous fistula, Tolosa-Hunt syndrome • Orbit: Trauma, tumor, infection

24. right cranial nerve III palsy

25. right cranial nerve VI palsy

27. 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

28. Voluntary Horizontal Saccades FEF FEF CEREBRAL HEMISPHERE III MIDBRAIN III PONS VI VI PPRF PPRF

29. Left MLF lesion – intranuclear ophthalmoplegia

30. LR MR MR LR III MIDBRAIN III PONS VI VI Yoking Mechanism

31. 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, Neuro-ophthalmology Emory University