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Vision Science 5 > Lecture 15 Objectives > Flashcards

Lecture 15 Objectives Flashcards

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1
Q

VOR stabilizes retinal images during ___ head movements.

A

Brief

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2
Q

How does VOR stabilize retinal images?

A

Counter-rotates eyes at the same speed as the head

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3
Q

Which is a pure reflex, VOR or OKN?

A

VOR

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4
Q

When does OKN stabilize the eyes?

A

During tracking of a large moving visual scene

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5
Q

Which directions are sensed by the semicircular canals?

A

Horizontal - yaw
Vertical - pitch
Torsional - roll

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6
Q

Which directions are sensed by the otolith organs?

A

Side to side - heave
Up and down - bob
For and aft - surge

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7
Q

The otolith organs consist of what?

A

The utricle and saccule

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8
Q

What is the associated contralateral EOM of the horizontal canal?

A

Lateral Rectus

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9
Q

What is the associated ipsilateral EOM associated with the horizontal canal?

A

Medial Rectus

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10
Q

What are the three characteristics of VOR?

A

Phase
Latency
Gain

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11
Q

What is the ideal phase shift for VOR?

A

0

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12
Q

What is the VOR phase shift in dark?

A

0

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13
Q

What is the VOR phase shift in light?

A

0

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14
Q

On what does the VOR gain depend?

A

Frequency of head motion

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15
Q

When is VOR gain usually induced?

A

During walking/running

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16
Q

What is the natural head rotation frequency?

A

0.5-5 Hz

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17
Q

What is VOR gain in the dark?

A

-0.9

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18
Q

What is VOR gain in the light?

A

-1.0

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19
Q

What is the dynamic torsional gain?

A

-0.4 to -0.7

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20
Q

What is the static torsional VOR gain?

A

-0.1 to -0.24

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21
Q

What is an example where VOR torsional gain would be in play?

A

Tilting head from shoulder to shoulder

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22
Q

What mediates static torsional VOR gain?

A

Otolith-ocular reflex from inputs from the utricles

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23
Q

What is VOR latency?

A

16msec

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24
Q

What is the pathway of the VOR excitatory 3 neuron arc?

A
  1. Signal from horizontal semicircular canal to MVN
  2. Signal from MVN to contralateral abducens nucleus
  3. Signal from abducens nucleus to ipsilateral lateral rectus
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25
Q

What is the pathway of the VOR excitatory 4 neuron arc?

A
  1. Signal from horizontal semicircular canal to MVN
  2. Signal from MVN to contralateral abducens nucleus
  3. Signal from abducens nucleus to ipsilateral lateral rectus
  4. Signal also from abducens sent through MLF to innervate the contralateral medial rectus
26
Q

What is the pathway of the inhibitory 3 neuron arc?

A
  1. Signal from horizontal semicircular canal to MVN
  2. Signal from MVN to ipsilateral abducens nucleus
  3. Signal from abducens nucleus to ipsilateral lateral rectus
27
Q

What is the pathway of the inhibitory 4 neuron arc?

A
  1. Signal from horizontal semicircular canal to MVN
  2. Signal from MVN to ipsilateral abducens nucleus
  3. Signal from abducens nucleus to ipsilateral lateral rectus
  4. Signal also from abducens nucleus
28
Q

What does an acute unilateral vestibular lesion cause?

A

Nystagmus

29
Q

In acute unilateral vestibular loss, which way will the eye turn?

A

Toward the lesion

30
Q

In unilateral vestibular loss, head shaking induced nystagmus will show the slow phase being directed toward what?

A

The paretic labyrinth

31
Q

What does COWS stand for?

A

Cold - opposite, Warm - same side

32
Q

Does COWS refer to quick phase or slow phase?

A

Quick phase

33
Q

Oscillopsia is a clinical sign of what?

A

Bilateral Vestibular loss

34
Q

What is oscillopsia?

A

The illusion of motion of the environment, which is exacerbated by head motion

35
Q

How do you test for bilateral vestibular loss?

A

Dynamic VA

36
Q

If there is bilateral vestibular loss, and you test with dynamic VA, what would the expected results be?

A

A loss of around 5 lines of VA

37
Q

What type of system controls VOR?

A

Open loop

38
Q

Because VOR is an open loop system, what must occur to keep the errors at a minimum?

A

Continuous calibration by short and long-term adaptations

39
Q

A hyperopic person wearing plus lenses has a ___ VOR gain.

A

Higher

40
Q

A myopic person wearing plus lenses has a ___ VOR gain.

A

Lower

41
Q

A person wearing minus power contacts has ___ VOR gain.

A

No difference

42
Q

How long does it take to adapt to new glasses?

A

Days to weeks

43
Q

Where does adaptation to new glasses take place in the brain?

A

Vestibular nucleus

Flocculus and paraflocculus

44
Q

What is the main movement of the optokinetic system?

A

Optokinetic nystagmus

45
Q

OKN is induced reflexively by what?

A

Motion of a large visual scene

46
Q

What is the function of the optokinetic system?

A

To supplement the angular VOR

47
Q

What does VOR respond best to?

A

Brief, high-frequency head rotation

48
Q

The optokinetic system sustains retinal image stability after ___ has ceased.

A

Vestibular responses

49
Q

Which type of OKN is entirely reflexive, passive or active?

A

Passive

50
Q

What acts as stimuli for active OKN?

A

Moving foveal images

51
Q

The stimuli for active OKN also can be stimuli for what?

A

Smooth pursuit and saccades

52
Q

T or F: the fast and slow phases of passive OKN look just like the phases of active OKN.

A

True

53
Q

What is a stimulus for passive OKN?

A

Movement of large objects

54
Q

Why are things of high spatial frequency poor stimuli for passive OKN?

A

Neurons for passive OKN don’t respond well to fine details

55
Q

Passive OKN is dominated by what?

A

Peripheral motion

56
Q

What is the latency of OKN?

A

140msec

57
Q

What is the slow phase gain of OKN?

A

0.8

58
Q

What is “noted” by a patient with infantile esotropia under monocular conditions?

A

Illusion of nasal motion

59
Q

What does infantile esotropia cause under monocular conditions?

A

Latent nystagmus

60
Q

T or F: a patient with infantile esotropia notices the same illusion whether binocular or monocular.

A

False

Vision Science 5 (8 decks)

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