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Eye movements, reflexes and control
01/20/2015 Virginia Lam Daniella Marks
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Component of pupillary reflex pathway
Afferent pathway: Optic disc, optic nerve (CNII), optic chiasm optic tract and pretectal nucleus (dorsal midbrain) Efferent pathway Oculomotor nerve Edinger westphal nucleus, ciliary ganglion
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Assessing pupillary reflexes
For integrity of pupillary light reflex pathway through pupil size and reaction Light reflex test Swinging flashlight test Accommodation Near reflex test
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Light reflex pathway
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Light reflex test Assess: How: Result:
CN II, III, optic tract, Pretectal nucleus, Edinger nucleus and ciliary ganglion How: Dim environment Ask patient to fixate a distant target Illuminate the right eye from right side, and left from left side Don’t stand in front of patient to avoid accommodation Result: Brisk simultaneous equal response on the pupil you shine light on (direct response) and contralateral pupil (consensual response) Good reference link:
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Swinging flashlight test
Assess: Compare the direct and consensual response of both eyes How: Same condition as light reflex test and check reflex first Then swing the light source rhythmically and swiftly from one eye to the other Observe what happen to the pupil of the eye you are shining light on, and its contralateral eye Result: Pupil should constrict or stay the same size If it dilates when light is shone on, it means the light reflex is seaker than consensual reflex, suggesting optic nerve pathology Abnormal response is known as relative affective pupillary defect (RAPD) or Marcus Gunn pupil NB: it is a comparative test, so no bilateral RAPD!
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Near reflex test Assess: How: Result: The ability to accommodate
Ask patient to focus on a distant target, and then a near point (about an arm length away) Observe the pupillary reflex and eye movement Result: Eye position: vergence Brisk pupillary constriction
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Pupil reflex Test: Shine light on right eye
CN II Lesion (complete): no direct and consensual CN III lesion (blue arrow): No direct but with consensual
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Argyll Robertson Pupil
Seen in tertiary neuro syphillis, but can also found in diabetic neuropathy Pupils can accommodate but do not react Affect Edinger Westphal nucleus
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Extrinsic Eye Muscle Function
(Up and In) (Down and In) Imagine each muscle as if it were acting alone.
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Testing the Muscles Step 1: put the muscle in relative isolation
Select new starting position (different from it’s neutral position Step 2: ask the patient to make a specific eye movement Step 3: observe whether patient is capable of moving eye
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Medial and Lateral Rectus
In this case, the actual movement and testing position are the same Medial rectus Actual movement: move pupil medially Test: ask patient to look toward their nose Lateral rectus Actual movement: move pupil laterally Test: ask patient to look toward their ears Nose MR = Adducts Nose LR = Abducts
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Inferior and Superior Rectus
Put the eye in a position where no other muscles are capable of moving eye Abducting the eye accomplishes this Now only looks at elevation/depression Inferior rectus Actual movement: downwards and inwards Test: ask the patient to look out and down Superior rectus Actual movement: upwards and outwards Test: ask the patient to look out and up Nose Nose
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Inferior and superior oblique
Put the eye in a position where no other muscles are capable of moving eye Adducting the eye accomplishes this Now only looks at elevation/depression Inferior oblique Actual movement: upwards and outwards Test: ask the patient to look in and up Superior oblique Actual movement: downwards and outwards Test: ask the patient to look in and down Nose Nose
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Eye Movements and Cranial Nerves
LR6 SO4 AO3 Lateral rectus – VI Superior oblique – IV All others - III
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Cranial Nerve Palsies CN Normal function Palsy CN III Motor supply to:
Levator palpebrae superioris MR, IR, SR, IO Autonomic motor supply to: Sphincter pupillae Ciliary body Motor function of affected eye: Ptosis Divergent squint – horizontal+vertical diplopia Autonomic function of affected eye: Dilated pupil Unreactive to direct/consensual light reflex CN IV SO Upward and extorsion deviation Torsional diplopia – patient will tilt head away from side of lesion (neck pain!) Vertical diplopia CN VI LR No lateral movement Convergent squint – horizontal diplopia
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Cranial Nerve Palsies Diplopia worsens when:
Unaffected eye looks away from lesion side Looking down (affected eye stuck in up+out position) Unaffected eye looks towards lesion side
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What are 3 types of eye movement control?
Track a target Stabilize a target Scan between targets
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What are 5 ways to control eye movements?
Medial longitudinal fasciculus (MLF) Lateral conjugate (together) gaze Voluntary saccades Quick flickers in response to stimuli Vestibulo-ocular reflex Stabilize the eyes to compensate for head movement Frontal eye field Visual attention and conjugate gaze Visual association areas Process information
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Internuclear Opthalmoplegia
E.g. Lesion in right MFL Patient looks right Right eye abducts (R CN VI), left eye adducts (L CN III) Patient looks left Right eye remains centered (R CN III), left eye abducts (L CN VI) Patient able to converge and accommodate eyes Horizontal diplopia worse when looking left Compensation: head slightly rotated to the left In damaged MLF: Side of MLF pathway damage results in ipsilateral damage in adduction Nuclei are intact – can still accommodate Note: this is the patient’s perspective.
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Vestibulo-ocular reflex
As the head is rotating axially in a given direction, the lateral semicircular canal makes both eyes look to opposite side Clinical relevance: Brain stem function testing Doll’s eye sign
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Vestibulo-Ocular Reflex
E.g. Head moves right Right SCC activated Stimulates right CN VIII Activates contralateral CN VI nucleus MLF activated Left CN VI activated (left lateral rectus) Right CN III activated (right medial rectus) Look left Damage: Eyes drift to side of lesion due to unopposed vestibular nuclear system on opposite side Damage: Eyes drift to side of lesion
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Nystagmus Fast and slow phase
Named according to the fast “flicker” Fast movement to the right, right nystagmus Consequence of damage to vestibulo-ocular system Remember: left VOR makes you look right Damage to left VOR: eyes drift to left (slow phase) Right nystagmus (fast phase to the right)
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Clinical Relevance of VOR and Nystagmus
Cold caloric test Imperative for assessing brain function Procedure Cold water is injected into the ear – affects SCC Eyes slowly drift to side of water (analogous to lesion) Fast correction to midline E.g. Water injected into left ear Left SCC affected Eyes drift to the left, right nystagmus to correct it Damage CNS depression: fast phase is not so fast… Coma/brain stem death: no reaction at all
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Question: Mr Smith visits your GP surgery, presenting with the following: What do you want to know in terms of Eye lid movement? Resting eye position? Vision?
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How is it different from Horner’s Syndrome?
Eye lid movement Can he open his eye? Eye position? What is his resting eye position How can it move Vision Any double vision When it is worse How is it different from Horner’s Syndrome?
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