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Eye movements, reflexes and control
01/20/2015
Virginia LamDaniella Marks
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
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
Light reflex pathway
Light reflex test
• Assess: – 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)
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!– https://www.youtube.com/watch?v=HSYo7LhfV3A
Near reflex test
• Assess:– The ability to accommodate
• How:– 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
Pupil reflexTest:Shine light on right eye
CN II Lesion (complete): no direct and consensual
CN III lesion (blue arrow):No direct but with consensual
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
Extrinsic Eye Muscle Function
Imagine each muscle as if it were acting alone.
(Down and In)
(Up and In)
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
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
MR = Adducts
Nose
LR = Abducts
Nose
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
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
Eye Movements and Cranial Nerves
LR6 SO4 AO3
Lateral rectus – VISuperior oblique – IV
All others - III
Cranial Nerve PalsiesCN Normal function Palsy
CN III Motor supply to:• Levator palpebrae superioris• MR, IR, SR, IOAutonomic motor supply to:• Sphincter pupillae • Ciliary body
Motor function of affected eye:• Ptosis• Divergent squint – horizontal+vertical diplopiaAutonomic function of affected eye:• Dilated pupil• Unreactive to direct/consensual light reflex
CN IV Motor supply to:• SO
Motor function of affected eye:• Upward and extorsion deviationoTorsional diplopia – patient will tilt head away from side of lesion (neck pain!)oVertical diplopia
CN VI Motor supply to:• LR
Motor function of affected eye:• No lateral movement • Convergent squint – horizontal diplopia
Cranial Nerve PalsiesDiplopia worsens when:
Unaffected eye looks away from lesion side
Looking down (affected eye stuck in up+out position)
Unaffected eye looks towards lesion side
What are 3 types of eye movement control?
• Track a target• Stabilize a target• Scan between targets
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
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
Note: this is the patient’s perspective.
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
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
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)
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
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?
• 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?