Neuro: 3.06 - Control Of Eye Movements

Front 1

What is the purpose of eye movements?

Back 1

- Maintain visual input on center of macula, FOVEA, where visual acuity is highest due to high density of cones
- Ability to fixate

Front 2

What kind of movements are needed to fixate on an object?

Back 2

- Horizontally / Vertically
- Converge / Diverge
- Conjugate eye movements - yoked together

Front 3

Which pathway mainly keeps the eyes together?

Back 3

Medial Longitudinal Fasciculus (MLF)

Front 4

What are the two systems for eye movements?

Back 4

- Fast, voluntary system - Saccadic system
- Slow, involuntary system

Front 5

What are the components of the Fast Eye Movement system? Functions?

Back 5

Saccades - voluntarily brings objects in peripheral vision onto fovea (under cortical control)

Front 6

What are the components of the Slow Eye Movement system? Functions?

Back 6

- Smooth pursuit system - voluntarily follow a moving object (cortex)
- Vestibulo-ocular reflex (VOR) - involuntarily coordinate eye and head movement to stabilize object on fovea (vestibular system)
- Optokinetic system - involuntarily stabilizes object on fovea during sustained head rotations

Front 7

How do the fast and slow eye movement systems come together to move the ey?

Back 7

Final common pathway - cranial nerve nuclei involved in extraocular movement

Front 8

What are two main symptoms related to eye control?

Back 8

- Diplopia
- Nystagmus

Front 9

What is Diplopia?

Back 9

Double vision - neurological issue (unlike blurred vision)

Front 10

What causes diplopia?

Back 10

Image not resting on the fovea of each eye due to muscle, NMJ, nerve, or CNS disorder

Front 11

What is blurred vision? Cause?

Back 11

- Decreased visual acuity
- Neurological or non-neurological cause
- E.g., corneal abrasion, optic neuritis, etc.

Front 12

What is Nystagmus?

Back 12

Fast oscillatory eye movements (more than 1-2 beats)

Front 13

What causes nystagmus?

Back 13

- Defect of slow eye movement system (usually impaired VOR)
- Need to have intact cortex (frontal eye fields) to get nystagmus

Front 14

What are the phases of the Nystagmus?

Back 14

- Fast phase - mediated by cortex
- Slow phase - VOR not working (R nystagmus = L VOR not working)

Front 15

If the patients eyes are beating vertically (vertical nystagmus), what is the cause?

Back 15

ALWAYS a CNS lesion

Front 16

If the patients eyes are beating horizontally or rotationally (horizontal or rotational nystagmus), what is the cause?

Back 16

CNS or PNS lesion

Front 17

What nucleus helps eyes move horizontally?

Back 17

Abducens Nucleus/PPRF = Horizontal Gaze Center

Front 18

How do you get your eyes to simultaneously look L?

Back 18

L abducens nucleus / PPRF --> moves both eyes to L:
- L CN VI pulls L lateral rectus to move eye L
- Sends signal to R CN III to pull R medial rectus to move eye L

Front 19

What is the function of the Medial Longitudinal Fasciculus (MLF)?

Back 19

- Yolks eyes together
- Helps contralateral eye adduct (look medially)

Front 20

What is the term for a lesion to the Medial Longitudinal Fasciculus (MLF) of one side? What happens?

Back 20

- Internuclear Ophthalmoplegia (INO)
- R MLF lesion causes R INO, R eye does not adduct and L eye has nystagmus on leftward gaze
- L eye nystagmus because of double vision (due to R eye not adducting)

Front 21

When there is a lesion to the MLF (causing internuclear ophthalmoplegia, INO), what causes the other eye to have a nystagmus?

Back 21

- Double vision due to other eye not adducting)
- VOR moves eye back towards nose, but because of instructions to look away from nose, the cortex overrides (suppresses VOR) and moves it back where you want it to look
- Looks like the eye with nystagmus is trying to "pull" the other eye over

Front 22

What's wrong in this patient?
(Only one eye moves towards right)

Back 22

- Lesion to right abducens nerve (CN VI palsy)
- R lateral rectus is not moving eye adequately, innervated by R CN VI)
(Lesion 1)

Front 23

What's wrong in this patient?
(Neither eye moves towards right)

Back 23

- Lesion (2) to right abducens nucleus (R lateral gaze palsy)
OR
- Lesion (3) to right PPRF (R lateral gaze palsy)

Front 24

What's wrong in this patient?

Back 24

- Lesion (4) to L MLF (L INO)
- L eye won't move to right (no input to L medial rectus)
- R eye exhibits nystagmus due to double vision and opposing inputs from VOR/cortex

Front 25

What's wrong in this patient?

Back 25

- Lesion (5) to L MLF and L abducens nucleus (1-1/2 syndrome)
- Can't look left with either eye because of lesion to L abducens nucleus
- Can't look right with L eye because of lesion to L MLF
- R eye looking R has nystagmus due to opposing inputs from VOR / cortex

Front 26

What is the function of saccades? What mediates it?

Back 26

- Move eyes to object of interest (foveation) very quickly (>700 degrees/sec)
- Voluntary - mediated by cortex: contralateral Frontal Eye Fields (FEF)
* If you want to look quickly at something on your R, use L FEF

Front 27

What is the pathway to make you look to the R very quickly?

Back 27

- Activate L frontal eye fields (FEF)
- Activates R PPRF / Abducens Nucleus
- R CN VI - lateral rectus turns R eye to right
- L MLF activates L oculomotor nucleus & L CN III - medial rectus turns L eye to right
- Both eyes move right

Front 28

What are the two types of clinical consequences of lesions to the saccadic system?

Back 28

- Right-way eyes
- Wrong-way eyes

Front 29

What are the symptoms of Right-Way Eyes? Cause?

Back 29

- Contralateral hemiparesis
- Ipsilateral gaze preference
- Frontal Cortex lesion (lesion to side eyes are looking)

Front 30

Why is there contralateral hemiparesis and ipsilateral gaze preference in "right-way eyes"?

Back 30

- Contralateral hemiparesis - lesion of primary motor cortex
- Ipsilateral gaze preference - frontal eye field lesion does not allow saccading to opposite side, but opposite side FEF is still functional and causes eyes to look toward lesion

Front 31

What can cause "Right-Way Eyes"?

Back 31

Frontal cortex stroke (on side that the eyes are looking towards, opposite side of hemiparesis)

Front 32

What are the symptoms of "Wrong-Way Eyes"? Cause?

Back 32

- Contralateral hemiparesis
- Contralateral gaze preference
- Lesion to pons

Front 33

Why is there contralateral hemiparesis and contralateral gaze preference in "wrong-way eyes"?

Back 33

- Contralateral hemiparesis - L pontine corticobulbar / corticospinal tracts --> causes R body/face paresis
- Contralateral gaze preference - L PPRF/abducens nuclei lesion --> loss of L horizontal gaze center --> cannot look to left (so eyes deviate to R / contralateral side)

Front 34

What allows you to track a moving object smoothly?

Back 34

- Smooth pursuits
- If object is moving faster than ability of smooth pursuit system to follow, then saccadic system takes over

Front 35

What mediates the Smooth Pursuits system?

Back 35

- Parieto-Occipital-Temporal eye fields
- Stimulate ipsilateral PPRF/abducens nucleus
- Modulated by cerebellum (flocculonodulus)

Front 36

What happens if there is a lesion to smooth pursuit system?

Back 36

"Jerky" eye movements because saccades are being used instead

Front 37

What can cause "jerky" eye movements?

Back 37

- Lesion to smooth pursuits system (instead using saccades)
- R parietal-occipital-temporal lesion (jerkiness to R)
- Lesion of cerebellum can also cause jerky pursuits
- R parietal eye field lesion --> inability to pursue to R

Front 38

What mediates the Vestibulo-ocular reflex (VOR)?

Back 38

- Vestibular nuclei / nerve and semicircular canals (SCC)
- Influenced/inhibited by cerebellum (flocculonodular lobe)

Front 39

Which way does the VOR move your eyes?

Back 39

Contralaterally: if head moving to left, eyes move to right
- Specifically, turn head left, activating L ear horizontal SCC --> moves eyes to right

Front 40

What are the symptoms if the VOR is lesioned?

Back 40

- Every time you move head, images can't be stabilized on fovea
- Everything in field of vision will blur and result in lowered visual acuity (feeling dizzy too)

Front 41

What can cause the VOR to not work correctly?

Back 41

- Gentamycin toxicity
- Bilateral vestibular dysfunction

Front 42

How do you suppress the VOR?

Back 42

Cortex (such as FEF - frontal eye fields)

Front 43

What is wrong with this patient?

Back 43

- R CN VI lesion OR R Lateral Rectus lesion
- R eye is esotropic (inward) on primary gaze
- R eye does not fully abduct

Front 44

What is wrong with this patient?

Back 44

Impaired R eye adduction --> R Internuclear Ophthalmoplegia --> R Medial Longitudinal Fasciculus (MLF) lesioned

Front 45

What is wrong with this patient?

Back 45

- Cannot look L --> L horizontal gaze center lesion --> L abducens nucleus / PPRF
- Cannot look R --> R horizontal gaze center
- Intact up, down, convergence --> intact CN III and IV
* Bilateral Abducens nucleus / PPRF lesions

Front 46

What is wrong with this patient?

Back 46

- Impaired R eye adduction --> R INO --> R MLF
- Impaired R gaze --> R horizontal gaze center --> R abducens nucleus (and/or PPRF)
* 1-1/2 syndrome *