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Control Of Eye Movements Flashcards

1
Q

How are head movements transmitted for normal eye movements?

A

Via vestibular info

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2
Q

What selects a visual target?

A

Brainstem - superior colliculus

Cortical areas

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3
Q

What controls eye position?

A

MLF

Reflexes - VOR

Cerebral centers

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4
Q

What does supranuclear mean?

A

Brainstem

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5
Q

What are Saccades?

A

Rapid eye movement that brings image of object ONTO FOVEA

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6
Q

What do saccades use?

A

Frontal eye fields
Superior colliculus
Pontine Paramedian reticular formation

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7
Q

What are the effects of saccades?

A

Rapid conjugate deviation TOWARD opposite side

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8
Q

What does Smooth PUrsuit do?

A

Keeps MOVING IMAGE centered on fovea

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9
Q

What does smooth pursuit use to accomplish its goal?

A

Visual pathway
Parietooccipital cortex
Vestibulocerebellum

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10
Q

What is the effect of Smooth pursuit?

With respect to the parietooccipital cortex?

A

Conjugated deviation toward direction of movement of object

Same side to parietooccipital cortex

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11
Q

What is the Vestibulo-ocular system do?

A

Hold image stead on fovea during MOVING HEAD

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12
Q

What does the vestibulo-ocular system use?

A

Semicircular canals and vestibular nuclei

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13
Q

What is the effect of the vestibulo-ocular movement?

A

Conjugate deviation of eyes in opposite direction of head rotation

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14
Q

What does the optokinetic system do?

A

Hold images of the target steady on the RETINA during sustained HEAD ROTATION

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15
Q

What does the optokinetic system use?

A

Visual pathway
Parietooccipital cortex
Vestibulocerebellum and vestibular nuclei

(Same as smooth pursuit)

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16
Q

What is the effect of the optokinetic system?

A

Maintains deviation of eyes initiated by vestibuloocular reflex

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17
Q

What supranuclear gaze control system does dis-conjugate movement?

A

Vergence

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18
Q

What does the vergence system do?

A

Keeps image on fovea whether object is moved near or far away

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19
Q

What doe the vergence system use?

A

Unknown direct input to CN 3s; (via interneurons?)

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20
Q

What is the effect of Vergence?

A

Accommodation to near target by moving eyes in opposite directions so that images of a single object are placed on both foveas

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21
Q

What do the frontal eye fields do?

A

Voluntary saccades

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22
Q

What do superior colliculus do?

A

Reflexive saccades

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23
Q

What is the horizontal gaze center of the saccadic system?

A

Paramedian pontine reticular formation (PPRF)

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24
Q

What would happen if you damaged the PPRF on the left side?

A

Could not look left

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25
Q

What are the horizontal saccadic nuclei?

A

CN 6, CN3

Connected by MLF

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26
Q

With the horiz. Saccadic system, if the RIGHT frontal eye fields were stimulated at the middle frontal gyrus, what would eyes do?

A

Look left

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27
Q

What is the pathway for the Horizontal Saccadic System?

A

R. Frontal Eye field —> PPRF —> nucleus 6 —> MLF —> nucleus 3

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28
Q

What are the control mechanisms for the Horizontal Saccadic System?

A

Frontal eye fields
Superior COlliculus
Paramedian pontine reticular formation
Horiz. Nuclei (6 and 3, via MLF)

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29
Q

What are the Control mechanisms for the Vertical Saccadic system?

A

Frontal eye fields
Superior colliculus
Rostral interstitial Nucleus of the MLF (RiMLF)
Vertical Nuclei (3, 4)

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30
Q

What is the vertical gaze center in the Vertical Saccadic system?

A

Rostral interstitial Nucleus of the MLF (RiMLF)

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31
Q

What are the vertical nuclei of the vertical saccadic system?

A

Cn 3

Cn 4

32
Q

Wher is the RiMLF ?

A

In rostral midbrain near Superior Colliculus and near posterior commissure

33
Q

What could cause a problem with vertical saccades?

A

If region near RiMLF is compressed via a pineal tumor

34
Q

What will cause the patient to have trouble looking down?

A

If region near interstitial nucleus of Cajal is compressed

35
Q

How does the brainstem control saccadic movements?

3 steps

A
  1. Burst of neuronal firing
    via excitatory burst neurons to MOVE eye toward targets
  2. Tonic neuronal firing
    Via tonic neurons to LOCK onto target
  3. Pause neurons to INHIBIT BURST neurons
    So no more movements
36
Q

What are the burst, tonic, and pause neurons of the horizontal saccadic system?

A

Burst: PPRF

Tonic: Nucleus preposition hypoglossi

Pause: Omnipause cells of raphe nuclei

37
Q

what are the burst, tonic and pause nuerons of the vertical saccadic system?

A

Burst: RiMLF

Tonic: interstitial nucleus of Cajal

Pause: Omnipause cells of raphe nuclei

38
Q

What level is the horizontal gaze control center at?

A

Pons

PPRF

39
Q

What level is the vertical gaze control center at?

A

Midbrain

RiMLF

40
Q

With the Saccadic system, if the right hemisphere is activated, how will you look?

A

Look left

opposite of hemi activated

41
Q

With the Smooth Pursuit system, if the right hemisphere is activated, how will you look?

A

Look left

Will be same as hemi activated

42
Q

What are reflex saccadic eye movemnt done by?

A

Supeiror colliculus (and supplementary and parietal eye fields)

43
Q

How do you test saccadic movements?

A

Ask patient to visually jump from one object to another

44
Q

If the frontal gaze center has a destructive lesion to it, what happens to the eyes?

What could cause this?

A

Look TOWARD side of lesion

(Transient conjugate eye deviation toward side of lesion)

Stroke

45
Q

What happens if there is seizure activity in the frontal gaze center?

A

Eye deviates AWAY from the firing gaze center

Seizure - irritating —> look AWAY

46
Q

What are the control mechanisms for the Smooth Pursuit system?

A

Parietooccipital junction (brodmann’ s area 19)

Pons

Vestibulocerebellum

Medial vestibular nuclei
(horiz. 3 & 6, vert. 3 & 4)

47
Q

How do you test the Smooth Pursuit system?

A

Ask pt. To track slow moving object

Optokinetic tape - move tape thru fingers in front of patients

48
Q

What is the pathway for the Smooth Pursuit system?

A

Parietooccipital-occipital junction —>

Pontine nuclei —> Vestibulocerebellum

—> vestibular nuclei —> CN 6 —> MLF —> CN 3

(Or cn 4 and 3 for vertical smooth pursuit)

49
Q

What happens to the smooth pursuit system if the partial lobe is lesioned?

A

Loss of smooth pursuit movements TOWARD side of lesion

No optokinetic nystagmus when tape is moved toward damaged lobe

50
Q

What does the optokinetic system use?

A

Smooth pursuit pathway

Nuclei of accessory optic system

51
Q

What is optokinetic nystagmus? (OKN)

A

Eye will make a quick move in the opposite direction when visual target is broken at end of visual field

52
Q

What do you need for OKN to occur?

A

Intact parietooccipital eye field

53
Q

What is the pathway for the Optokinetic system?

A

Area 14 —> Vis. Assoc. Center —> Nuclie of accessory optic system and nucleus of the optic tract —> POns

Pons —> vestibulocerebellum —> vestibular nuerlci —> Nuclei 3, 4, 6,

Pons —> Inferior olive —> cerebrocerebellum —> corrects movement errors

54
Q

What are the control mechanisms for the vestibulo-ocular system?

A

Semicircular ducts
Cn 8
Vestibular nuclei
(Horiz. 6 and 3; vertical 3 and 4)

55
Q

What will movement to the right of the head activate in the vestibulo-ocular system?

A

Right labyrinth

56
Q

How will the eyes move when the head is turned right according to VO system?

A

Eyes will go left (think Doll’s eye)

57
Q

How do you test the Vestibulo-ocular system/

A

Doll’s eye maneuver

Ice water caloric test

58
Q

With the he ice water caloric test, how will eyes deviate?

A

Deviate toward irrigated ear

W/ quick corrective jerk Opposite

COld opposite, warm away

59
Q

If a comatose patient has an absent doll’s eyes and ice water caloric test, what will that tell you?

A

Dysfunction of brainstem

60
Q

What is the pathway for the vestibulo-ocular system?

A

Head turns —-> activates same side labyrinth —> CN 8 —> vestibular nuclei —> nucleus 6 —> MLF —> nucleus 3

61
Q

What is INO characterized by?

A

Impaired horizontal eye movements

Weak adduction of affected eye
(L. Eye can’t look right)

Abduction nystagmus of opposite eye

62
Q

What does INO result from?

A

Lesion of MLF in pons or midbrain

63
Q

Who do we see INO in?

A

Pts. W/ MS

64
Q

If the LEFT MLF is lesioned, what will occur?

A

LEFT eye wont look RIGHT

Left INO

65
Q

What happens if the LEFT Abducens NUCLEUS is lesioned?

A

Both eyes can’t look LEFT

66
Q

what happens if the LEFT CN 6 Nerve is lesioned?

A

LEFT eye wont look LEFT

67
Q

What are the control mechanisms for Vergence?

A

Unknown input to CN 3 neurons, most likely thru interneurons

68
Q

How do you test Vergence?

A

Ask pt. To focus on near object, watch for near object reflex (convergence, accomodation, pupillary constriction)

69
Q

What is a pathology of the vergence system?

A

Argyll Robertson pupil

70
Q

What can cause argyll Robertson pupil?

A

Neurosyphylis

71
Q

How does an Argyll RObertson pupil present?

A

NO pupil constriction w/ LIGHT

BUT

Pupil CONSTRICTION w/ NEAR REFLEX

72
Q

What are the components of the near reflex?

A

Accomodation

Convergence

Pupillary constriction

73
Q

How can we still have convergence with INO?

A

Because convergence does not use MLF

74
Q

What is convergence?

A

Eyes together so that image is on the fovea

75
Q

What is accomodation?

A

Lens thickens - for near images
Lens thins - for distant

So that image is focused on fovea

76
Q

What is the pupillary constriction for?

A

Better optical performance by focusing light

77
Q

What are the steps in the near reflex ?

A
  1. Normal visual pathway
  2. Visual association area
  3. Superior colliculus or pretectal area

SC —> CN 3 nucleus —> both MRs to converge eyes

Pretectal area —> EW nucleus —> pupillary constriction

.. (19 decks)

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