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III. Binocular Vision > Fixation Disparity, Binocular Rivalry, and Panum's Area (F) > Flashcards

Fixation Disparity, Binocular Rivalry, and Panum's Area (F) Flashcards

1
Q

What is the equation for the rate of rivalry?

A

1/(t(L) + t(R))
t(L) = time of seeing/cycle left eye
t(R) = time of seeing/cycle right eye

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2
Q

What is suppression on the orthoscope considered? 1. How does this develop? 2

A
  1. pathological suppression

2. often non-strabismic binocular vision disorders exhibit central suppresion

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3
Q

What do both the associated and dissociated phorias indicate?

A

convergence position of eyes where no fusional vergence is needed to fuse

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4
Q

How can diplopia be eliminated with anomalous retinal correspondence?

A

corresponding points shift so that common images in each eye now correspond (enable suppression and might facilitate fusion)

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5
Q

During rivalry, what is the suppression area size in order to eliminate confusion equal to?

A

Panum’s area (minimum gap size)

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6
Q

Why is it that if you flash targets for a brief time of flicker then the suppression zone may not be evident?

A
  1. development of rivalry takes time (>200ms)

2. Panum’s areas are small for brief exposures

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7
Q

When looking at the Forced vergence fixation disparity curve, what is the point where the line crosses the vertical line called? 1. The horizontal line? 2

A
  1. habitual fixation disparity

2. associated phoria

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8
Q

Is rivalry synchronous or asynchronous for large fields? 1. Small fields? 2

A
  1. asynchronous

2. synchronous

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9
Q

What causes people to experience SOLI instead of the desired SILO?

A

accommodative convergence micropsia because not using vergence as cue but using size change as the cue

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10
Q

What does the elliptical shape of Panum’s area lead to clinically?

A

inducing diplopia takes much less prism vertically than horizontally

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11
Q

How do you measure Panum’s area?

A

Panum’s area apparatus that measures the range of single vision laterally

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12
Q

What is the term for using convergence to free fuse a dioptic target?

A

chiastopic fusion

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13
Q

Does higher contrast provide more or less signal strength?

A

more

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14
Q

How do patients with strabismus avoid diplopia?

A
  1. change in retinal correspondence (ARC) to shift Panum’s area
  2. enlargement of Panum’s area
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15
Q

If the top arrow of a Borish card (OD) is at the letter A (on the right) and the bottom arrow (OS) is on the number 1 (on the left), what is the direction and magnitude of the fixation disparity?

A

20’ eso

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16
Q

How does luminance viewing with both eyes compare to that of viewing with one eye?

A

sum of the luminances of the two eyes

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17
Q

What is the maximum fixation disparity size?

A

when point of regard is at the edge of Panum’s area

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18
Q

How does increasing the contrast in the left eye impact the rivalry?

A

t(L) is same. t(R) decreases. Rate increases. Relative predominance increases for the left eye

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19
Q

What is the term for using divergence to free fuse a dioptic target?

A

orthopic fusion

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20
Q

What are the different devices or objects to measure the fixation disparity in a patient?

A
  1. Nonius line method
  2. disparometer
  3. Borish card
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21
Q

What is the subjective method to measure fixation disparity that uses monocular vertical lines to allow the subject to visualize the oculocentric direction of the eye?

A

Nonius Line Method

22
Q

Is a cover test a associated phoria or a dissociated phoria value?

A

dissociated

23
Q

Under what conditions is Panum’s the largest? 1. What is the shape of Panum’s area here? 2

A
  1. low temporal and spatial frequency

2. elliptical

24
Q

What is the disparity at the far and near limits of single binocular vision equal to?

A

1/2 size of Panum’s area

25
Q

What is the “chrome” like appearance that occurs if right and left luminances differ greatly called? 1. What amount must the difference be? 2

A
  1. luster

2. > 10:1

26
Q

What is the power of contralateral suppression called?

A

stimulus strength

27
Q

How do patients with strabismus avoid confusion?

A
  1. normal (rivalry) suppression eliminates confusion near corresponding points (within Panum’s area)
  2. suppression gets “embedded” in strabismus (fixing eye becomes dominant and rate of rivalry becomes slow)
28
Q

What are the factors influencing stimulus strength during rivalry?

A
  1. target contrast

2. contrast sensitivity of the eye

29
Q

When there is a purposeful error, what does fixation disparity provide?

A

stimulus to fusional vergence

30
Q

What does SILO mean?

A

small in (closer to me), large out (further away)

31
Q

Is the fusional vergence response always more or less than the stimulus?

A

less

32
Q

What is the contrast sensitivity of the eye influenced by?

A
  1. light adaptation

2. retinal eccentricity

33
Q

What is an area in the retina of one eye, which when stimulated simultaneously with a point in the retina of the other eye provides single binocular vision called?

A

Panum’s area

34
Q

What is a constant of proportionality relating fusional vergence to fixation disparity called? 1. What is the equation for this? 2

A
  1. gain

2. gain = fusional vergence/FD

35
Q

What is the idea that binocular luminance is the weighted sum of the monocular luminances?

A

Levelt’s Law of Complementary Shares

36
Q

What is an ocular deviation less than the size of the diplopia threshold called?

A

fixation disparity

37
Q

What is the angular size of Panum’s area equal to?

A

angle between inner and outer limits

38
Q

How does brightness viewing with both eyes compare to that of viewing with one eye?

A

the same

39
Q

How does increasing the contrast in both eyes impact the rivalry?

A

t(L) decreases. t(R) decreases. Rate increases. Relative predominance unchanged

40
Q

What does the difference between each number or letter on the Borish card represent in magnitude?

A

10 minutes or arc

41
Q

Does fixation disparity increase or decrease the measure Panum’s area?

A

increasesby the size of PA for the fovea

42
Q

Does Panum’s area increase or decrease with an increase in spatial frequency?

A

decrease

43
Q

What is the relationship between fixation disparity and fusional vergence (Ogle curve)?

A

Forced vergence fixation disparity curve

44
Q

What is the idea that duration of the impression of one eye (t(L) or t(R)) decreases as the stimulus strength in the other eye increases?

A

Levelt’s Law

45
Q

How does decreasing the contrast in the left eye impact the rivalry?

A

t(L) is same. t(R) increases. Rate decreases. Relative predominance increases for the right eye

46
Q

What is the phoria type that removes the stimulus to fusional vergence so eyes assume posture where fusional vergence equals zero?

A

dissociated phoria

47
Q

How can diplopia be eliminated with normal correspondence?

A

enlargement of Panum’s area (with only image from dominant eye being seen)

48
Q

What is the phoria type that finds the position of eyes where input to maintain fusional vergence is zero so fusional vergence must be zero?

A

associated phoria

49
Q

Does Panum’s area increase or decrease with an increase in temporal frequency (shorter duration)?

A

decrease

50
Q

During rivalry, how is confusion eliminated?

A

alternate suppression of one eye

III. Binocular Vision (15 decks)

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