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Oc Motility > Week 2 > Flashcards

Week 2 Flashcards

1
Q

WIT: Image is held steadily on the fovea by the eye and head

A

Fixation

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2
Q

What 3 purposes is there for fixation?

A
  1. to see stationary object
  2. for 20/20 vision
  3. To study targets of high spatial frequency
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3
Q

For fixation to occur, motion of the image on the fovea can be NO MORE than ___ degrees per second

A

5 degrees/sec

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4
Q

For fixation, image should like within ___ degrees of the center of fovea

A

0.5 degrees

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5
Q

Is a tremor a conjugate movement between the 2 eyes?

A

No

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6
Q

Microsaccades correct for ____.

A

Drifts

MS is larger by 4x in peripheral positions of gaze

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7
Q

Microsaccades occure how many times per second in all directions?

A

1-5 times

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8
Q

Are MS correlated between the two eyes in (1) time of onset and (2) direction?

A

Yes, but many not be correlated in amplitude

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9
Q

By concentrating, can you suppress MS?

A

Yes!

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10
Q

WIT: Deviation from the point of fixation of about 0.1 deg (6mins) w/ a velocity of about 0.25 deg/sec

A

Drifts

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11
Q

Can drifts occur in opposite directions in the two eyes?

A

Yes

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12
Q

In darkness, velocity of drifts increase by ___.

A

4x

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13
Q

WIT: Visual cues to fixate are important for steady control of gaze called ?

A

Field holding reflex

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14
Q

Fixation + Saccades = ?

A

Reading

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15
Q

WIT: Illusion of motion, caused by a nystagmus disrupting steady fixation

A

Oscillopsia

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16
Q

WIT: Initial slow-phase drift w/ fast reset

A

Pathological nystagmus

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17
Q

WIT: Small, less than 2 degree movement, this starts with an abnormal saccade

A

Saccadic intrusions

- more common in smokers, medications and caffeine ppl

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18
Q

What is an abnormal saccadic intrusion?

A

Anything more than 20/min

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19
Q

WIT: Repetitive to and from movment of the eyes initiated by slow phases

A

Nystagmus

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20
Q

What is the vertical gaze holding NI?

A

Interstitial Nucleus of Cajal

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21
Q

What is the horiontal gaze holding NI?

A

NPH - Nucleus Prepositus Hypoglossi

MVN - Medial Vestibular Nuclei

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22
Q

What part of the cerebellum is important for gaze holding?

A

Flocculus

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23
Q

What neurotransmitters to the NI use?

A

ACH
GABA
NMDA

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24
Q

A leaky neural integrator create a mismatch between what 2 things?

A

Pulse and Step!

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25
Q

WIT: Pulse signal keeps attempting to move eye to eccentric position but eye keeps drifting back due to fault step signal

A

Gaze- evoked nystagmus

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26
Q

When attempting to look back in primary gaze after adapting to gaze-evoked nystamus you get what?

A

Rebound nystagmus

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27
Q

WIT: Slow, large nystagmus toward thel lesion (R), but rapid small nystagmus away from lesion (L)

A

Brun’s nystagmus

28
Q

Brun’s nystagmus occurs in ___% of large acoustic tumors > 3.5 cm

A

11%

29
Q

What disorder occurs when there’s a lesion in the MLF?

A

Internuclear Ophthalmoplegia (INO)

30
Q

What controls horizontal conjugate gaze?

A

Abducen’s nucleus in pons

31
Q

With a lesion to the LEFT abducen’s nucleus causing a horizontal gaze palsy, what results?

A
  1. No VOR

2. No left gaze (pt can’t look left)

32
Q

Lesion of the right MLF, what happens?

A
  1. INO

2. Right eye cannot adduct (Abducen’s nucleus can’t tell MR to adduct for left gaze)

33
Q

Is there such thing as a normal endpoint nystagmus?

A

Yes, dampens after 3 beats

34
Q

What is the most common cause of gaze-evoked nystagmus?

A

A drug side effect (sedatives, tranquilizers, anticonvulsants, alcohol)

35
Q

WIT: Occurs naturally during sustained self-rotation in the light or stimulated by motion of the VF

A

Optokinetic Nystagmus

36
Q

What are the 3 dynamics of OKN?

A
  1. Gain
  2. Frequency
  3. Amplitude
37
Q

WIT: the ratio of slow phase velocity to stimulus velocity

A

Gain

38
Q

WIT: the extent of each slow phase excursion

A

Amplitude

39
Q

WIT: The rate at which the gaze is reset by the fast phase

A

Frequency

40
Q

What is the purpose of OKAN?

A

To help neutralize PRN

41
Q

What is the purpose of OKN/OKR?

A

To stabilize images on the retina

42
Q

What is circularvection?

A

The sensation of self-rotation, feeling like we’re moving

  • becomes more sensative w/ age
43
Q

What factors affect OKN?

A
  1. Target Luminance
  2. Spatial Frequency
  3. Velocity of Target Motion
  4. Direction (gain is highest horiontally)
  5. Torsion (watching a revolving disk)
44
Q

When does VOR tend to stop?

A

When acceleration = 0 and there’s a constant velocity

45
Q

What type of VOR do ice skaters use when doing long high-speed spins

A

VOR Habituation - VoR adjust and adapts to a changing environment

46
Q

Since OKN is a reflex, it must be ____ to follow a small moving target. What other eye movement do you use to suppress this?

A

Suppressed

Smooth pursuits

47
Q

What is the first neural pathway to develop? What’s another name for it

A

NOT - Nucleus of Optic Tract

Subcortical pathway

48
Q

What is the second neural pathway to develop? What’s another name for it?

A

MT, MST, PP

Higher Level Cortical Pathway

49
Q

The subcortical pathway for OKN is mediated by what two things?

A

Accessory Optic System (AOS) and Nucleus of Optic Tract (NOT)

50
Q

The cortical Pathway is mediated by what pathway?

A

Geniculo-Striate Pathway

51
Q

Naso-temporal asymmetry is observed when visual cortex is not well-developed in who?

A

Infants, amblyopes, albinos

52
Q

In under-developed cortex, what direction dominates?

A

Naso-Temporal direction dominates

53
Q

Infants show OKN asymmetry until about what month?

A

2 months

54
Q

OKN is much stronger for monocular stimulus toward _____?

A

toward the nose (drum is rotating toward the nose, temporal –> nasal)

55
Q

T or F: In normal adults, there is no assymetry evident.

A

True, cortex is fully developed

56
Q

What are the 2 consequences of the VN providing information to the sensory cortex?

A
  1. Vestibular Sensation = circularvection

2. Ability to distinguish between self-motion and environmental motion

57
Q

The ability to distinguish between self-motion and environmental motion aids in what?

A

helps to maintain sense of stability during locomotion

58
Q

The VN-complex receives feedback and feed-forward inputs from many areas, that allow for the effectiveness of ?

A

Vision Therapy - ability to improve one’s eye movements

59
Q

What are the 4 types of nystagmus?

A
  1. Vestibular
  2. Gaze-Evoked
  3. Congenital Jerk
  4. Pendular
60
Q

WIT: Constant velocity drift of the eyes w/ quick phases, vestibular disease

A

Vestibular Nystagmus

61
Q

WIT: Drift back to center, negative exponential slow phase

A

Gaze-evoked

62
Q

WIT: Well-defined slow and fast phases, Positive exponential waveform, sometimes found in amblyopia

A

Jerk Nystagmus

63
Q

NO defined fast-phase, found in patients with known foveal disorder

A

Pendulum Nystagmus

64
Q

What are the 2 types of congenital nystagmus?

A
  1. Latent/Jerk Nystagmus

2. Pendulum Nystagmus

65
Q

T or F: Latent/Jerk nystagmus only occurs when the eye is occluded

A

True

66
Q

What are the 4 different treatments for nystagmus?

A
  1. Pharmaceutical (muscle relaxant)
  2. BCVA, w/ CL
  3. Find Null Point w/ prisms or surgery
  4. Vision Therapy

Oc Motility (10 decks)

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