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Ocular Motility > VOR > Flashcards

VOR Flashcards

1
Q

Why do we need reflex eye movements that stabilize images on the retina during head movement?

A

decreases potential retinal image motion– prevents blurred images and can prevent oscillopsia

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2
Q

How do we stabilize images on the retina during head movements?

A

by producing an eye movement in the direction opposite head movement

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3
Q

What is the point of adaptive head and eye movements?

A

preserves the image on the center of the visual field

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4
Q

What are the two component parts of Vestibular-Optokinetic movments?

A

vestibular system and optokinetic system

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5
Q

What is the general idea of the vestibular system?

A

compensates for brief, transient head movements, produces VOR

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6
Q

What is the general idea of the optokinetic system?

A

compensates for prolonged, sustained movements, low frequency, aided by pursuit system, result is OKN

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7
Q

How to vestibular and optokinetic movements interact?

A

over time VOR declines, responds to acceleration/deceleration, when that becomes constant VOR breaks down and optokinetic takes over to hold image stable until rotation is finished

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8
Q

When rotation is complete, we should get a…

A

nystagmus in the opposite direction

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9
Q

T/F the optokinetic system does not account for nystagmus

A

false

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10
Q

What is OKAN?

A

optokinetic after-nystagmus

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11
Q

What does OKAN do?

A

helps cancel out the post-rotational nystagmus and minimizes vertigo

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12
Q

Describe VOR movements

A

head moved quickly to 1 side while eyes stay on target, eye position in orbit is opposite head motion in space, result: keep eye position in space constant

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13
Q

What does OKAN result from?

A

velocity storage phenomenon

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14
Q

What is the velocity storage phenomenon?

A

indirect central neuro integrating circuit activated by initial input of rotational acceleration and velocity, stores velocity info and discharges in after the input has ceased

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15
Q

What is the stimulus for VOR?

A

angular or rotational acceleration, acceleration info integrated into head velocity signal and integrated again to get head displacement

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16
Q

Describe what happens during VOR with brain injury?

A

when head rotated to the right, eyes moved to the right and then made a compensatory movement back to the target

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17
Q

What three additional thing does VOR serve to maintain?

A

body posture, equilibrium, and muscle tone

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18
Q

How many semicircular canals are each side and what do they sense?

A

3, sense angular acceleration when fluid hits the cupula and deflects it

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19
Q

What is the cupula?

A

gel like substance containing crista ampullaris that sends a neurological/electrical signal to the CNS

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20
Q

What do the maculae of the saccule and utricle and the otoliths sense?

A

transient linear accelerations and static head tilt

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21
Q

What contains endolymph?

A

the endolymphatic space of the semicircular canal

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22
Q

What are otoliths?

A

calcium particles that sit on top of the gelatin in the macula of the saccule or utricle

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23
Q

What are otoliths affected by?

A

gravity and inertia

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24
Q

When do the otoliths stay in place?

A

when the head is level

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25
Q

What forces take place when walking forward?

A

acceleration forward, inertial force opposite of acceleration, gravity, and resultant from inertia and gravity

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26
Q

What are the otolith forces with a head tilt?

A

gravity and gravitational component in the plane of the otoliths creates resultant force

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27
Q

What is the result of head tilt?

A

translational VOR with total latency a bit longer, 35 msec

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28
Q

What do the best runners do?

A

keep head relatively still and suppress VOR to an extent

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29
Q

Why do runners suppress VOR to some extent?

A

prevents disruptive, conflicting info between internal and external inputs

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30
Q

VOR displacement?

A

10 to 20 degrees

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31
Q

VOR peak head velocity?

A

100 to 250 deg/sec (constant velocity means OKN)

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32
Q

VOR peak head acceleration?

A

1000 to 2500 deg/sec^2 (trigger for VOR)

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33
Q

VOR latency?

A

15 msec (shortest)

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34
Q

Is VOR gain better for horizontal or vertical?

A

horizontal, barely

35
Q

T/F fluid movement is in the same direction as head movement

A

false

36
Q

What makes a gain greater than 1.0?

A

eye movement > head movement

37
Q

Is VOR gain present in congenitally blind people?

A

no, need early normal visual experience for development

38
Q

What happens to VOR with acquired blindness?

A

reduced VOR, visual experience is needed for maintenance

39
Q

T/F VOR is less accurate in infants

A

true

40
Q

T/F VOR can compensate for optical magnification changes

A

true

41
Q

What happens to VOR gain with minus lenses?

A

patient needs less gain for a given head rotation

42
Q

What happens to VOR gain with plus lenses?

A

hyperope needs more gain, around 2.5% per diopter

43
Q

T/F VOR gain effects take place with contact lenses and spectacle lenses

A

false, does NOT happen w/ CLs

44
Q

What happens to patients with lesions of the cerebellum?

A

patients lose visual inhibition of the VOR reflex, adaptation response

45
Q

T/F each canal has connections to more than one EOM

A

true, not 1:1 canal:EOM ratio

46
Q

T/F each canal has either excitatory or inhibitory connections

A

false, each canal has both

47
Q

What structure are VOR EOM connections passing through?

A

medial longitudinal fasciculus

48
Q

With head translation, result is…

A

opposite eye movement and otolith movement

49
Q

With head tilt, result is… counter-roll of the eye

A

counter-roll of the eye

50
Q

T/F VOR translation and tilt have different neuro pathways

A

true

51
Q

T/F injury to the side/back of the head impacts VOR

A

true

52
Q

What is ICS impulse?

A

new tech for testing eye movements

53
Q

What does ICS impulse test?

A

VOR, BPPV, other vestibular disorders, nystagmus, gaze position, skew deviation

54
Q

In the VOR data of a healthy subject gain is ___ and one side should ___ the other

A

1.0, balance

55
Q

Describe VOR data with bilateral loss

A

lots of catch up saccades to stay on target, gain is symmetric but bad 0.3-0.4, patient has some symptoms

56
Q

Describe VOR data with unilateral loss

A

asymmetric gain (one bad one normal) and overt saccades, patient has severe symptoms

57
Q

T/F after time passes, gain recovers after acute loss

A

true

58
Q

What is benign paroxysmal postural vertigo?

A

disorder caused by problem in inner ear, symptom=positional vertigo, spinning sensation after change in head position

59
Q

Why does BPPV happen and what is the cure?

A

happens when an otolith gets stuck in a semicircular canal and hit cupula, fixed with epley maneuver to get crystal back in place in the saccule/utricle

60
Q

What is optokinetic nystagmus?

A

involuntary jerk nystagmus induced by motion of the visual field, not the fovea

61
Q

What triggers OKN?

A

repetitive stimuli, sustained, low frequency

62
Q

What is the neural integrator for OKN?

A

nucleus of the ophthalmic tract

63
Q

What is the pathway?

A

semicircular canals to primary vestibular nerve to vestibular nucleus to sec vestibular neurons to medial longitudinal fasciculus to oculomotor neurons

64
Q

What is the OKN specific pathway?

A

retina to visual cortex to dorsal terminal nucleus of the ophthalmic tract to nucleus of the ophthalmic tract to inferior olive to cerebellum to vestibular nuclei oculomotor nuclei

65
Q

In the OKN system, ___ retina dominates

A

peripheral

66
Q

How does a deep central scotoma affect OKN?

A

reduction of gain by only 10-30%

67
Q

T/F OKN is heavily affected by blur

A

false, not affected much by blur

68
Q

What is the latency for OKN?

A

140 msec

69
Q

Is the image clear in OKN?

A

no image is stable but not clear

70
Q

How do horizontal and vertical gain values compare?

A

similar but vertical degrades faster as target moves faster

71
Q

What is gain with torsion?

A

.03 low

72
Q

T/F OKN declines with age

A

true

73
Q

T/F all speeds of optokinetic drum trigger the reflex

A

false, only certain ranges trigger the reflex, too fast=blur

74
Q

In children how are temporal to nasal and nasal to temporal OKN different?

A

nasal to temporal OKN is not intact as infant, temporal to nasal is intact

75
Q

When do the two directions of OKN equalize in babies?

A

directions equalize between 3 and 6 months

76
Q

What happens in children whose OKN on each eye does not equalize?

A

high tendency for strabismus, usually esotropia

77
Q

Describe functional amblyopia

A

asymmetric, reduced response, similar to neurological disease, especially found in congenital ET/strabismic amblyopia

78
Q

What are the three vestibular disorders?

A

unilateral peripheral (acute), bilateral peripheral (acute), and central (lots of problems)

79
Q

What are the two subtypes of unilateral peripheral vestibular disorder?

A

transient imbalance, spontaneous nystagmus

80
Q

What is the subtype of bilateral peripheral vestibular disorder?

A

oscillopsia (world tilt), decreased vision

81
Q

Describe nystagmus in unilateral

A

slow phase toward lesion

82
Q

Describe nystagmus in bilateral

A

decreased vision, inadequate compensation from VOR

83
Q

Describe congenital nystagmus?

A

asymmetric, reduced gain

84
Q

Describe neurological disease/developmental delay or VOR/OKN

A

newborns have decreased nasal to temporal, anterior/cortical lesions of the visual pathway

Ocular Motility (13 decks)

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