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Motility > Theory and Facts (Ex 1) > Flashcards

Theory and Facts (Ex 1) Flashcards

1
Q

What is the Nativism theory?

A

Herring said that binocular vision is not learned but rather acquired through evolution. As in we are not born with it.

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2
Q

Empiricism

A

a theory that binocular vision is learned although the it requires certain anatomical features. (helmholtz)

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3
Q

What are the advantages of 2 or more eyes?

A 
enrichment of perception
ease of dexterity
security
lower performance threshold
larger overall visual  fields
stereopsis
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4
Q

What are the disadvantages of 2 or more eyes?

A 
The Neural control of eye position
Cortical integration 
Confusion 
Rivalry
Diplopia
Amblyopia
Strabismus
Aniseikonia
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5
Q

How does eye position change as we ascend the hierarchial order?

A

changes from lateral to frontal

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6
Q

What is special about the eye placement of the swollow?

A

It has 2 foveas.

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7
Q

What animal has a 360 deg view?

A

Almost all prey animals, but frogs have a panoramic view.

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8
Q

What is the total visual field of humans?

A

200, about 120deg is binocular, and around 30 for each eye

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9
Q

What is an open loop system?

A

A control with no feed back. It is unregulated an can be unstable and lead to being driven to its breaking point.

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10
Q

What is a closed loop system?

A

The control system has a feedback. Either positive, or negative.

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11
Q

When is the Fovea formed and how?

A

Fovea is antecedent to CNS maturation. 3 months after postpartum the foveal pit is formed.

  • progressive migration of the cones toward the center
  • increased density of foveal cones
  • cone cell elongation
  • decrease in intersegmental diameter, outersegments of cones are relatively unchanged.
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12
Q

What is a chiasmal decusation and how does it differ in different animals?

A

Optic nerve fibers to the brain decussate at the chiasm before terminating at the geniculate body. Decusation is total in lower animald and partial higher up the hierarchy.
Extent of cross over inversely related to size of binocular VF.
Owl has 100% uncrossed fibers and size of binocular vision is 30 deg.
Horse: 13%, 65° binocular VF.
Dog: 33%, 98° BVF
Primates: 50%, 124- 200° BVF

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13
Q

How do cells that respond to vision form in the brain?

A

Binocularity arises in the striate cortex by equipping 1 cell with 2 receptive fields. In cortical receptive fields, excitatory and inhibitory fields are powerful and elongated than circular. These cells are higly selective for orientation and localization.
Occlusion of 1 eye during development or critical period, leads to the cortical cell population that is blind to that eye.

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14
Q

What are the signs of sensory dominance in an eye?

A

The eye:

  • whose image is seen more frequently in binocular rivalry
  • with better VA
  • has the more substantial seeming image in physiological diplopia
  • whose after image persists longer
  • image is less readily ignored.
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15
Q

What are the signs of motor dominance in an eye?

A

The eye:

  • used to sight (sharp shooter)
  • in which percieved image jump/shift is lesser in alternate cover test
  • when closed causes subjects movemtn to have greater instability.
  • less profound herings lateral shift
  • with smaller fixation disparity, heterophoria, or heterotropia
  • fixates at far.
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16
Q

What determines correlative dominance in an eye?

A

The eye:

  • before which a card is held to read
  • on the side of the dominant hand.
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17
Q

Why do foveas have smaller receptive fields?

A

So we can see finer details.

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18
Q

Which muscles originate. From the superior mesodermal complex?

A 
SO
SR
LEVATOR PALPEBRAE
Part of the:
- MR
-LR
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19
Q

Which Muscles originate from the inferior Mesodermal complex?

A

-IO
- IR
Part of:
- MR
- LR

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20
Q

Which muscles originate from the Annulus of Zinn?

A 
-MR
LR
SR
IR
SO
Levator Palpebrae
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21
Q

Which EOM does not originate at the annulus of Zinn?

A

IO

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22
Q

How far away are the insertions of each EOM from the iris?

A

SR: 7.9
LR: 7.0
IR: 6.6
MR: 5.8

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23
Q

What are the positions of the inferior rectus?

A
  • when adducted 67°: action is extortion
  • in primary position: depression, adduction, extorsion
  • when abducted 23°: depression
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24
Q

What are the positions of the SO?

A
  • when adducted 51°: depressor of globe
  • primary position: intorts, abducts the eye
  • when abducted 39°: intorsion.
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25
Q

Positions of the IO

A
  • when adducted 51° elevation of globe
  • primary position: elevation, extortion, adduction
  • when abducted 39°: extorsion.
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26
Q

Isolated contraction of MR

A

1ry: adduction

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27
Q

Isolated contraction of LR

A

1ry: abduction

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28
Q

Isolated contraction of IR

A

1ry: depression
2ry: excyclo
3ry: adduction

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29
Q

Isolated contraction of SR

A

1ry: elevation
2ry: incyclo
3ry: adduction

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30
Q

Isolated contraction of IO

A

1ry: Excyclo
2ry: elevation
3ry: abduction

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31
Q

What are the yoked muscles used in dexrtoversion?

A

Right gaze

RLR and LMR

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32
Q

What are the yoked muscles used in levoversion?

A

LLR and RMR

Left gaze

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33
Q

What are the yoked muscles used in dextrodeosumversion?

A

Down and Right

RIR & LSO

34
Q

What are the yoked muscles used in levodeosumversion?

A

Down and Left

LIR & RSO

35
Q

What are the yoked muscles used in dextrosursumversion?

A

Up & Right

RSR & LIO

36
Q

What are the yoked muscles used in Levosursumversion?

A

Up and Left

LSR & RIO

37
Q

What is the law that talks about yoked muscles?

A

Hering’s Law of equal innervation (motor correspondence)

38
Q

What are the Fick’s axes??

A

1) The axis for horizontal side to side movement is the Z axis
2) The Axis for vertical up & Down movement is the X- axis
3) The Axis for torsional movements is the Y axis.

39
Q

What is true torsion?

A

Rotation only about the anterior- posterior axis as the eye is moved from the primary position to a tertiary position.

40
Q

What is false torsion?

A

The apparent cyclo-rotation of the eye determined by the difference between the objective vertical and the vertical corneal meridian in the tertiary position when 3iary position involves translation about the x and z axes.

41
Q

What is Listing’s Law?

A

There is only 1 unique tilt associated with any tertiary eye position.
This fundamental law of the oculomotor system has a neurophysiological basis.

42
Q

What is Donder’s Law?

A

In the absence of a head tilt, and with stationary visual surroundings, the degree of torsion measured relative to any system of axes is uniquely determined by the degree of horizontal and vertical rotations and “ Is the same for any particular degree of rotation about the other axes, regardless of the manner in which the eye arrives at it.

43
Q

What is Sherrington’s innervation law

A

on each eyeball there are 3 pairs of muscles which are mutually antagonistic in accordance with the reciprocal innervation law of Sherrington.

  • There is No movement of the eye that is produced by a single EOM contraction.
  • Each EOM has a given tone for every position of gaze.
44
Q

What is Hering’s equal innervation law?

A

There are intraorbital muscles that co-contract to elicit similar directional movement of the globe. Such muscle groups are called synergists.
- in binocular viewing, Hering’s equal innervation law is evoked to maintain conjugate eye movements, and the inter-ocular muscle pairs that move the eyes in a common direction are said to be yoked muscles.

45
Q

What are the properties of the Medial rectus

A

The strongest EOM.

  • used to converge the eyes into near gaze.
  • agonist of adduction and antagonist of abduction.
  • innervated by the CN3
46
Q

What are the properties of the Lateral Rectus?

A
  • innervated by CN 6
    (LR6SO4)
  • agonist of abduction and antagonist of adduction.
47
Q

What are the properties of the Superior Rectus?

A
  • Elevate the eye
  • rotate the eye nasally from the 12 o clock position. (2ry action)
  • adduction when contracted from the primary position ( 3ry action)
  • innervated by CN 3
  • in their 3ry action SR and IR work together, but opposite in 2ry action.
48
Q

What are the properties of the Inferior Rectus?

A

-1ry depress the eye
-2ry extort
-3ry adduction
in their 3ry action SR and IR work together, but opposite in 2ry action.
-CN 3 innervation

49
Q

What are the properties of the superior oblique?

A

1ry: intortion
2ry: depression
3ry: abduction
innervated by CN 4

50
Q

What are the properties of the SO?

A

1ry: extorsion
2ry: elevation
3ry: abduction

51
Q

Look in notebook for

A

the X diagram showing muscles.

52
Q

What does the broad H test do?

A
  • tests the horizontal and vertical acting muscles.
  • tests the field of action of each muscle.
    ( Field of action is the field where a certain muscle has the greatest action).
53
Q

What are the 2 main components of fusion?

A

sensory fusion and motor fusion.

54
Q

What is the alternation theory?

A

It is a sensory fusion theory.
- the 2 monocular views mutually inhibit each other. there exists a healthy competition for registry in consciosness of the monocular images from the right and left eyes ( binocular rivalry).
- There does not exist truly simultaneous process.
REACTION TIME EXPERIMENTS DISPROVE THE ALTERNATION THEORY OF FUSION..
( The picture where 2 different lines come together and make a mosaic looking picture).

55
Q

Rivalry fusion

A

periodic or intermittent extinction of brightness,or color from perception as a result of stimulation of the other eye. It indicates unstable fluctuation between competing components.
Dominance is expressed as exclusive or mosaic

56
Q

Binocular luster

A

retinal correspondence

in opposite contrast signs.

57
Q

What is Worth’s sensory fusion classification?

A
  • simultaneous perception (1st deg):
    This results when simulatneous information transfeer from both eyes occurs at the cortex
  • flat fusion (2nd deg): corresponding retinal element have afferent fibers that transverse the visual pathway to terminate on a common neural center- the hypothetical fusion center, binocular summation is evoked. the result is called FLAT fusion.
  • Depth perception (3rd deg): sensory fusion process is compromised when a sufficient dissimilarities exist in the image resolution, image form and image location of the 2 eyes.
58
Q

motor alternation processing theory

A

it proposed an interocular point by point signal register stimulation of corresponding retinal points has temporal interval of t.
- The theory recognizes retinal correspondence, but does not accept the theory of simultaneous perception.
this alternation process is relatively slow and fails to account for rapid fusion reflex which is stereopsis.

59
Q

heterophoria

A

fusion free position of the eyes

- when there is no need for fusion the dissociated eye assumes at rest position

60
Q

What is the fusional vergence movement in esophoria?

A

divergence

61
Q

What is the fusional vergence demand in exophoria?

A

convergence.

62
Q

What happens when motor fusion demand is uncompensated?

A

Strabismus results.

63
Q

What is motor fusion?

A

The ability to maintain a single fused image during vergence movements.

64
Q

What classifies as a Grade II fusion?

A

superimposition is sustained through a range of distances or vergence.

65
Q

What is chiastopic fusion?

A

BO eye are crossed

66
Q

What is orthopic fusion?

A

BI eyes are uncrossed.

67
Q

What is SILO phenomenon?

A

a patient experiences perceptual changes.

  • when convergence demand increases and fusion is maintained, target appears smaller and closer.
  • when divergence demand is increased and patient continues to maintain fusion, target will appear larger and further.
68
Q

What is the underlying basis for SILO?

A

size constancy

  • retinal size image increases as target is closer.
  • to compensate, the patient corrects it cognitively by shrinking the size of the image (shrinkage adjustment)
  • opposite is expansion adjustment
69
Q

What is SOLI?

A

Small out, Large in

  • whether a patient reports SOLI or SILO depends on if size consistency or vergence provides the cue to depth.
  • patient is looking at vectogram and sees target becoming smaller, so from past experiences patient assumes that target is moving further away.
  • more likely to be responded by adults.
70
Q

What are triggers for motor-fusion to regain bifixation?

A

diplopia and visual confusion.

71
Q

What is shallow suppression?

A

When suppression is present but diplopia or sensory fusion occurs readily

72
Q

When is suppression deep?

A

If suppression is sustained without diplopia or sensory fusion. Foveal and central suppressions tend to be the deepest and most resistant to therapy.

73
Q

What is laterality in suppression?

A

When the same eye is always suppressed, it is unilateral. This can be reversed by adjusting luminance, image contrast and other stimulus parameters

74
Q

What is fast-flashing suppression?

A

A latency period of viewing a target is needed for suppression. When the time interval for viewing is shortened by fast- flashing suppression is broken, and diplopia or sensory fusion occurs.

75
Q

What instrument measures suppression zone?

A

stereo-campimeter

76
Q

What area is spared in suppression zone?

A

in strabismus without fusion, the entire retina or the deviating eye is the suppression zone, except for the temporal crescent.

77
Q

Normal suppression

A

If suppression results from competition between corresponding points namely the fovea

78
Q

abnormal suppression

A

when suppression is between non-corresponding points.

79
Q

What is used to CLASSIFY and MEASURE suppression

A

vectrograph slides, worth -4 dot,

80
Q

If a patient sees a spot of light alternating between amber and green when a flicker of green spot of light is presented to the RE, and a red spot is presented to the LE,
Name 2 binocular conditions in this patient?

A

Partial suppression of LE and RE dominance with rivalry because light is amber and not red.

Motility (6 decks)

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