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Vision Science 5 > Lecture 15 Objectives > Flashcards

Lecture 15 Objectives Flashcards

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
What is the pathway of the VOR excitatory 4 neuron arc?
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
What is the pathway of the inhibitory 3 neuron arc?
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
What is the pathway of the inhibitory 4 neuron arc?
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
What does an acute unilateral vestibular lesion cause?
Nystagmus
29
In acute unilateral vestibular loss, which way will the eye turn?
Toward the lesion
30
In unilateral vestibular loss, head shaking induced nystagmus will show the slow phase being directed toward what?
The paretic labyrinth
31
What does COWS stand for?
Cold - opposite, Warm - same side
32
Does COWS refer to quick phase or slow phase?
Quick phase
33
Oscillopsia is a clinical sign of what?
Bilateral Vestibular loss
34
What is oscillopsia?
The illusion of motion of the environment, which is exacerbated by head motion
35
How do you test for bilateral vestibular loss?
Dynamic VA
36
If there is bilateral vestibular loss, and you test with dynamic VA, what would the expected results be?
A loss of around 5 lines of VA
37
What type of system controls VOR?
Open loop
38
Because VOR is an open loop system, what must occur to keep the errors at a minimum?
Continuous calibration by short and long-term adaptations
39
A hyperopic person wearing plus lenses has a ___ VOR gain.
Higher
40
A myopic person wearing plus lenses has a ___ VOR gain.
Lower
41
A person wearing minus power contacts has ___ VOR gain.
No difference
42
How long does it take to adapt to new glasses?
Days to weeks
43
Where does adaptation to new glasses take place in the brain?
Vestibular nucleus | Flocculus and paraflocculus
44
What is the main movement of the optokinetic system?
Optokinetic nystagmus
45
OKN is induced reflexively by what?
Motion of a large visual scene
46
What is the function of the optokinetic system?
To supplement the angular VOR
47
What does VOR respond best to?
Brief, high-frequency head rotation
48
The optokinetic system sustains retinal image stability after ___ has ceased.
Vestibular responses
49
Which type of OKN is entirely reflexive, passive or active?
Passive
50
What acts as stimuli for active OKN?
Moving foveal images
51
The stimuli for active OKN also can be stimuli for what?
Smooth pursuit and saccades
52
T or F: the fast and slow phases of passive OKN look just like the phases of active OKN.
True
53
What is a stimulus for passive OKN?
Movement of large objects
54
Why are things of high spatial frequency poor stimuli for passive OKN?
Neurons for passive OKN don't respond well to fine details
55
Passive OKN is dominated by what?
Peripheral motion
56
What is the latency of OKN?
140msec
57
What is the slow phase gain of OKN?
0.8
58
What is "noted" by a patient with infantile esotropia under monocular conditions?
Illusion of nasal motion
59
What does infantile esotropia cause under monocular conditions?
Latent nystagmus
60
T or F: a patient with infantile esotropia notices the same illusion whether binocular or monocular.
False

Vision Science 5 (8 decks)

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