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?