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Chika- SF2 > Control of Eye Movement- Graf > Flashcards

Control of Eye Movement- Graf Flashcards

1
Q

compensatory eye movements for the vestibulo-ocular reflex

A

has lots of involvement from the cerebellum and cortex

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2
Q

What is the innervation for the extraocular muscles?

A

LR6-SO4-R3

Oculomotor nucleus:

  • superior rectus (CONTRALATERAL projection)
  • medial rectus (ipsilateral projection)
  • lateral rectus (ipsilateral projection)
  • inferior oblique (ipsilateral projection)

Trochlear nucleus:
-superior oblique (CONTRALATERAL projection)

Abducens nucleus:
-lateral rectus (ipsilateral projection)

Abducens internuclear neuron pathway to CONTRALATERAL medial rectus MNs

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3
Q

Which extraocular eye muscles receive contralateral projections for their innervation?

A
  • superior oblique

- superior rectus

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4
Q

How can superior oblique palsy be caused?

A

a problems with the cerebellum????

-the superior medullary velum (anterior medullary velum) is a thin, transparent lamina of white matter, which stretches between the superior cerebellar peduncles

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5
Q

What is the horizontal eye movement saccade generator?

A

paramedian pontine reticular formation

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6
Q

What is the vertical eye movement saccade generator?

A
  • rostral interstitial nucleus of the medial longitudinal fasciculus
  • mesencephalic reticular formation
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7
Q

What is the underlying scheme to produce eye movements and many other reflex motor movements?

A

they are organized in vestibular coordinates

vertical axis makes horizontal eye movements and muscles

nasoccipital axis

bioral axis which makes nodding movements

RALP is the plane for the axis of the right anterior and left posterior canal

LARP is the plane for the axis of the left anterior and right posterior canal

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8
Q

Traditionally how have eye movements been described?

A

vertical eye movements

horizontal eye movements

torsion: rotation about the optic axis

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9
Q

Which extraocular muscles only have primary actions?

A

medial rectus: adduction

lateral rectus: abduction

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10
Q

What are the secondary actions of superior rectus?

A

secondary: intorsion, adduction
primary: elevation

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11
Q

What are the secondary actions of the inferior rectus?

A

secondary: extorsion, adduction
primary: depression

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12
Q

What are the secondary action of superior oblique?

A

secondary: depression, abduction
primary: intorsion

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13
Q

What are the secondary actions of inferior oblique?

A

secondary: elevation, abduction
primary: extorsion

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14
Q

What are the trajectories of all vertical extraocular muscles?

A

all of them have curved trajectories

all of them have vertical and torsional components

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15
Q

Semicircular canal and certain eye muscles have a spatial relationship. Explain.

A

anterior canal has a spatial relationship with the vertical recti

posterior semicircular canal has a spatial relationship with the oblique

horizontal semicircular canal has a spatial relationship with the horizontal recti

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16
Q

To make pure torsional or vertical eye movements what is required?

A

co-contraction of at least TWO eye muscles

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17
Q

If you want to have a vertical upward eye movement, what muscles are needed?

A

superior rectus and inferior oblique

superior rectus: elevation, intorsion, adduction

inferior oblique: extorsion, elevation, abduction

adduction and abduction cancel out; intorsion and extorsion cancel out

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18
Q

If you want to have a vertical downward eye movement, what muscles are needed?

A

inferior rectus and superior oblique

inferior rectus: depression, extorsion, adduction

superior oblique: intorsion, depression, abduction

adduction and abduction cancel out; intorsion and extorsion cancel out

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19
Q

What is nystagmus?

A
  • occurs as a result of a disequilibrium in neuronal circuits, or as a testing vehicle in the laboratory
  • there is no “nystagmus center” per se
  • resetting phase=fast phase
  • compensatory phase= slow phase
  • nystagmus has been named by the fast phase
  • compensatory left slow phase so nystagmus is right

if i turn pt to the right continuously then abruptly turn her to the left, her eyes turn left to compensate (slow phase) but then to the right (fast phase)

so there is right nystagmus

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20
Q

What is the compensatory eye movements AKA vestibulo-ocular reflex?

A
  • a very fast reflex
  • follows after latency of 16 msec
  • travel distance at 55 mi/h= 0.40 m
  • moves the over an equal but opposite distance that the head has traveled
  • when I move the head 10 degrees to the right the eyes need to move 10 degrees to the left; to keep the visual image stabilized so that we have sharp vision

Generation of compensatory eye movements:
acceleration (detection of movement) –> velocity (mechanical integration) –> position (neuronal integration)

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21
Q

What is the optokinetic reflex?

A

The optokinetic reflex (OKR), which serves to stabilize a moving image on the retina, is a behavioral response that has many favorable attributes as a test of CNS function

place pt in a chair and rotate striped wall or piece of paper

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22
Q

What is saccades?

A
  • fast, tracking
  • very fast eye movements to look at different targets
  • the most common eye movements we do everything

-saccadic eye movements shift the fovea rapidly to a target with a speed of up to 900 deg/sec

Equivalent to a speed of 9 m/sec (i.e. 20 mi/h) in a standard laboratory situation (looking at a curved surface at a distance of 57 cm).

-saccades are initiated in the cortex; if the cortex is lesioned you remove the input to the PPRP

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23
Q

What is smooth pursuit?

A
  • slow, tracking
  • smooth pursuit eye movements keep the image of a moving target on the fovea
  • control of smooth pursuit involves the cerebral cortex, the cerebellum and the pons
  • inputs arise from the motion-sensitive regions in the superior temporal sulcus (MT/MST: V5) and the frontal eye fields

MT=The middle temporal visual area (MT or V5) is a region of extrastriate visual cortex.

MST= Middle superior temporal

-smooth pursuit cannot be done voluntarily you need a target to do it!!!

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24
Q

What is fixation?

A
  • is an active process
  • holds the eyes still during intent gaze to allow examination of stationary object
  • the eyes must stay still in the orbits
  • this requires active suppression of eye movements
  • the most rostral portion of the superior colliculus has a representation of the fovea
  • neurons there discharge strongly during active fixation
25
Q

What is vergence?

A
  • when we look at an object that is close to us, our eyes rotate close to each other, or converge
  • vergence/divergence neurons are found on top of the oculomotor nucleus (III)
26
Q

What is divergence?

A
  • when we look at an object further away, the eyes rotate away from each other or diverge
  • vergence/divergence neurons are found on top of the oculomotor nucleus (III)
27
Q

What are conjugate movements and how is it related to double vision?

A

conjugate movements: eyes move into the same direction at the same time

if the eyes don’t have conjugate movements then double vision results

28
Q

What are conjugate movements and how is it related to double vision?

A

conjugate movements: eyes move into the same direction at the same time

if the eyes don’t have conjugate movements (disconjugate movements) then double vision results

double vision= diplopia

29
Q

Vergence and divergence has what type of conjugacy in their eye movements?

A

disconjugate eye movements

we cannot normally diverge the eyes from the primary position; occurs with epileptic seizures

30
Q

Vestibulo-ocular reflex, optokinetic reflex, saccades, smooth pursuit, and fixation have what type of conjugacy in their eye movements?

A

conjugate eye movements

31
Q

What is vestibular stimulation?

A

detection of acceleration ONLY

32
Q

What is the position integrator network?

A

if I look at something and look at another thing; it is an active process to look at

gaze holding means fixating on something; it is an active problem; if a pt cannot fixate then it is called leaky integrator

33
Q

Describe the three neuron arc of the vestibulo-ocular reflex.

A
  • Posterior canal sends excitatory connections to the ipsilateral SO and contralateral IR; sends inhibitory connections to the antagonist muscles of SO and IR to ipsilateral IO and contralateral SR
  • Horizontal canal sends excitatory connections to ipsilateral MR and contralateral LR; sends inhibitory connections to ipsilateral LR and contralateral MR
  • Anterior canal sends excitatory connections to ipsilateral SR and contralateral IO; sends inhibitory connections to ipsilateral IR and contralateral SO
34
Q

Explain the purpose of the abducen interneuron.

A

-specialized horizontal eye movement circuitry with three-neuron-arc link to abducens motoneurons and surrogate neuron i.e. the abducens internuclear neuron to the contralateral medial rectus motoneurons for production of horizontal conjugate eye movements (Hering’s Law of equal innervation of eye movers)

Allows flow of information from the contralateral abducens nuclei to the

35
Q

What is internuclear ophthalmoplegia?

A
  • causes palsy of the medial rectus muscle which is innervated by the affected abducens internuclear neuron, leading to a deficit in adduction in the affected eye and horizontal double vision
  • inability to adduct the eye across the midline on the affected side
36
Q

The pathway that converges the eye is independent of the internuclear pathway. Explain.

A
  • There is deficit in adducting the eye but not converging the eye.
  • This shows the abducens internuclear neuron (in between the abducens nuclei and medial rectus) stimulating medial rectus is affected.

The abducens nuclei is NOT affected as lateral rectus is still intact.

37
Q

What does a superior oblique palsy look like?

A

extorted and elevated eye

38
Q

What is gaze?

A

eye and head coordination

39
Q

What is ocular tilt reaction?

A
  • an isolated problem with the posterior canal pathway thus affecting:
  • ipsilateral inferior oblique and contralateral superior rectus
  • thus you have compensatory eye movements and compensatory head tilt
  • restoring equilibrium will involve elevating the eye which is on the contralateral side of the head tilt
40
Q

What is Wallenberg syndrome?

A
  • one of the most common causes for ocular tilt reaction
  • is a brain stem ischemia that is caused by a severed posterior inferior cerebellar artery
  • results in unilateral paramedian thalamic infarction
  • symptoms include difficulties with swallowing, hoarseness, dizziness, nausea, and vomiting, nystagmus, and problems with balance and gait coordination
  • lack of pain and temperature sensation on only one side of the face may occur, or a pattern of symptoms on opposite sides of the body, such as paralysis or numbness in the right side of the face, with weak or numb limbs on the left side
41
Q

The vestibular and visual systems are closely linked.

What is the visual-vestibular fusion?

A

when you move the head to the right then my eyes move to the left

the eyes follow the slipping world to the left so the compensatory phase is following the world visually

the visual input and vestibular input are complementary and synergistically

move strip to the left, eyes go to the left and reset to the right

42
Q

What are the brain regions involved in the optokinetic nystagmus?

A
  • cortex: visual cortex areas V1/V2/V4/V6A, areas MT/MST, area VIP, Frontal Eye Fields (FEF), PIVC (vestibular cortex) is inhibited
  • areas in the cerebellar hemispheres (culmen)
43
Q

Voluntary saccades are controlled by the cerebral cortex (Frontal eye fields/ supplementary eye fields) via what?

A

superior colliculus

44
Q

What is under the control of the caudate nucleus and suppresses superior colliculus output?

A

substantia nigra

45
Q

Lesions to where in the brain will results in humans having difficulties suppressing unwanted saccades?

A

frontal cortex

  • pt will look all around and cannot fixate
  • fixation is an active process and requires a lot of the circuitry
46
Q

Area LIP in the parietal cortex modulates what?

A

visual attention of saccade generation

47
Q

What is the result of lesions to the paramedian pontine reticular formation (PPRF)?

A

-ipsilateral gaze palsy: you cannot look to the same side to where the lesion is (if lesion is on the left then the pt cannot look to the left and will look to the right)

why does the pt have a hemiplegia?

  • involves a larger lesion of the pons and corticospinal tract which has not yet crossed (so you get a contralateral hemiplegia)
  • initially, eyes may deviate to contralateral

you can get PPRF through a lesion in the frontal eye fields which go to the PPRF

48
Q

Describe involuntary (reflex) eye movements.

A

-are three- dimensional

49
Q

Describe voluntary eye movements.

A
  • are two-dimensional

- lack the torsion component because they obey Listing’s Law

50
Q

Anyone with new glasses gets slightly dizzy in the beginning. Why?

A
  • your eye movements must match you head movements
  • your visual scene becomes slightly larger or smaller and your eye movements don’t match your head movements
  • but we have motor learning and adaptive plasticity to fix that
51
Q

What is the Marr-Albus theory?

A
  • cerebellum is involved in adaptive plasticity
  • when the vestibulo-ocular reflex that comes from the labyrinth
  • how do we know that the eye movement is correct?
  • the corrective input is the visual system which will then calibrate the reflex and this is coming from the eye to the cerebellum
  • the cerebellum then adjusts the synaptic quality of the input to the oculomotor neurons and makes a corrective eye movement
  • this is a mechanism we have all the time because neurons die and need to be replaced
  • in our body we have a constant recalibration of our reflexes, movement, etc.
52
Q

What is strabismus (squint)?

A
  • muscle imbalance resulting in misalignment of the visual axes of the two eyes
  • usually causes diplopia, and in children one image will be centrally suppressed resulting in later diminished visual acuity of the disused eye (amblyopia ex anopsia)
53
Q

What is the pupillary light reflex?

A
  • a consensual reflex that when light is shone on one eye the other eye constricts its pupil as well
  • there are ipsilateral retinal projections to the pretectal nuclei
  • we have ipsilateral projections from the temporal and contralateral projections from the nasal retina
  • they converge in the Edinger Westphal nucleus
54
Q

What is the result of lesion to the central or peripheral sympathetic nervous system? What are the symptoms involved?

A

Horner’s syndrome:

  • miosis
  • ptosis
  • enophthalmus
  • anhidrosis
55
Q

What is the nystagmography (EOG: electrooculogram)?

A

electrodes that measure the polarity of the eyeball

the eyeball at the retina is negative and in the front it is positive so there is potential differential

56
Q

What are frenzel goggles?

A

high power lenses to prevent fixation so that the physician can actually see the eye reflexes

57
Q

What is the scleral eye coil?

A

a scientific movement where you put a wire on the eye and it has some electronics

58
Q

What instrument measures ocular torsion?

A

laser ophthalmoscope

59
Q

What are some eye movement tests?

A
  • cover test (misalignment, heterotropia): tell pt to cover one eye and tell pt to look at nose
  • ocular following test: look at my nose and follow the finger with my eyes only
  • saccade test: snap my finger and pt looks at my finger
  • smooth pursuit test: pt follows my finger with the eyes only
  • gaze holding test: look at my finger; if there is a leaky integrator the eyes will drift away
  • vergence/divergence test : look at my finger and bring it back and forth towards and away from the pt
  • optokinetic test : Optokinetic nystagmus (OKN) is nystagmus that occurs in response to a rotation movement. It is present normally. The optokinetic response allows the eye to follow objects in motion when the head remains stationary
  • head jerk test

Chika- SF2 (63 decks)

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