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OD2-BVOM > Binocular Correspondence > Flashcards

Binocular Correspondence Flashcards

1
Q

what is hering’s 2nd law of visual direction

A

there is a retinal point to point relationship between the 2 eyes
-for every retinal point in one eye there is a corresponding retinal point in the fellow eye w/ an identical sense of visual direction

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2
Q

what is hering’s 3rd law

A

objects on the visual axis of either eye in symmetrical convergence appear to be on the median plane of the head (straight ahead)

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3
Q

what is a cyclopean direction

A

a single visual direction in the binocular visual field

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4
Q

binocular egocentric direction = ___+_____

A

cyclopean direction+gaze registration

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5
Q

cyclopean directions are analagous to…

A

oculocentric direction

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6
Q

all points on the retina have a binocular corresponding point except…

A

at the optic nerve head

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7
Q

normal correspondence only dpends on the retinal points being stimulated and is nnot affected by…

A 
image luminance 
contrast
color
size
orientation
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8
Q

normal correspondence is very stable, altered by …

A

only a few minutes of arc in the foveas, and then only by extreme fusional stress

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9
Q

what is spatial correspondnce a property of

A

the brain

also evident in the somatosensory system

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10
Q

what is binocular disparity

A

stimulation of noncorresponding points

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11
Q

each pair of corresponding oculocenric directions form a single….

A

cyclopean direction

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12
Q

what is a single visual direction in the binocular visual field

A

cylclopean direction

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13
Q

what are some synonyms of binocular disparity

A

retinal disparity

physiological disparity

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14
Q

what can crossed disparities stimulate

A
  1. steroscropic “nearness” if not a large amount of disparity
  2. crossed diplopia from disparity too large
  3. ocular convergence can be stimulated to look at the near object
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15
Q

what can uncrossed disparity stimulate

A
  1. stereoscopic “farness” if disparity small enough
  2. uncrossed diplopia disparity too large
  3. ocular divergnce to look at far object
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16
Q

what is the horopter

A

the set of points in physical space that can stimulate corresponding retinal points when eyes are converged to aim at a fixation point

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17
Q

how is the horopter shaped

A

bowl-shaped surface in near vision and flattens out as you look farther away

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18
Q

what is the best at the horopter

A

stereopsis and binocular summation

-single vision also occurs here

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19
Q

what is the veith-muller circle (VMO)

what question does it answer

A

theoretical horopter

“in principle, where should you put lights in physical space to stimulate corresponding points”

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20
Q

what does the VMO assume

A

eyes are identical and optically undisorted

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21
Q

what do objects in the VMo stimulate

A

zero binocular disparity

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22
Q

waht can objects in the peripheral vision stimulate

A

cross disparity
zero disparity
uncrossed disparity

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23
Q

where are the images for crossed disparity

where is it in relation to the VMO

A

images are more temporalward on the retinas, relative to corresponding opints
-inside the VMO

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24
Q

where are the images for uncrossed disparity

where is it in relation to the VMO

A

images are more nasalward on the retinas, relavtive to correspoinding points
-outside the VMO

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25
Q

what is the empirical horopter

A

answering the question “where do i have to put lights in physical space to stimulate corresponding points in this person”

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26
Q

what direction do we measure the horopter

A

horiztonal (longtidinal) direction

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27
Q

what are the additional rod adjustment criteria that measure an approximate horopter

A 
apparent fronto-parallel plane
equal distance
haplopia 
max stereo actuity
zero vergence
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28
Q

which methods of measuring the horopter don’t reflect the effects of fixation disparity

A

apparent fronto-parallel plane

equal distance

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29
Q

which method of measuring the horopter measures the extent of panum’s area

A

haplopia “single vision”

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30
Q

what will non zero vergence make you use to see an object

A

vergence eye movement

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31
Q

how does maximum stereoscopic acuity work

A

finer the stereoscropic threshold, the closer a point is in space to the horopter

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32
Q

what results does the spatial plot of the horopter show

A

ELH results

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33
Q

what are the 3 variables to quantify the ELH

A

relative curvature (hering-hillebrand deviation)
skew (horopter closer to right or left)
offset (how far off the fixation plane is the horopter displaced)

34
Q

does the normal horopter have more or less curvature than the VMO

A

normal has less than VMO bc of the asymmetry of the eye

35
Q

how do wedge prisms bend stereoscropic space

A

creates disparity where there shouldnt be any

36
Q

what does a large BO prism make a flat surface appear as?

what does a large BI prism do?

A

BO=concave (convex horopter)

BI=convex (concave horopter)

37
Q

is the ELH or the VMO more curved in a divergence excess intermittent exotropia

  • why is divergence stimulated
  • uncrossed or crossed disparity?
A

ELH more curved than VMO in near vision (only known conidition w/ this type of ELH)

  • most objects don’t fall on this horopter so stimulates divergecne (most of them are beyond this ELH)
  • uncrossed disparities in near fixation may result in their tendency to diverge
38
Q

what is skew a product of

A

horizontal aniseikonia

39
Q

what are small offsets caused by

A

fixation disparity (FD)

40
Q

waht does FD cause eyes to do

A

misconverge during bifxiation

41
Q

does FD disrupt fusion?

what does it reduce?

A

too small to disrupt fusion

steropsis may be reduced

42
Q

what is it called when the eyes converge too much

when the eyes converge not enough

A

too much = eso

too little = exo

43
Q

what are large offsets caused by

what is lost in a large offset

A

strabismus

central steropsis is lost

44
Q

what condition can cuase the horopter to have a small notch in it
-what is the notch called

A

esotropic strabismus

-flom notch

45
Q

what is the definition of anomalous retinal correspondence (ARC)

A
  • the centers of the foveas have diff visual directions

- the fovea of one eye has the same visual direction as a peripheral retinal point in the fellow eye

46
Q

when does ARC only occur in

A

early-onset strabismus

  • congenital OR
  • acquired (very early age)
47
Q

how can arc be a good predictor in the treatment of esotropia

A

arc present = less than 50% chance of cure
arc absent=better than 50% chance of cure

-arc prevents reflexive movements

48
Q

in testing correspondence, the purpose is…

A

to show whether correspondence is bifoveal

49
Q

when will there be correspondence

A

when both eyes are being used

50
Q

what is testing ARC based on

A

visual direction judgements

51
Q

when does ARC sometimes disappear

A

in total darkness

52
Q

why does it not work if we test correspondence based on fusion? stereopsis?

A

patient still may be able to fuse if non correscpoinding points are stimulated
-same with stereopsis, patients with arc may present w/ normal stereo

53
Q

how must the test targets be in testing correspondence

A

the test targets for both eyes must be unfusible but simultaneously visible (so we can assure that we are testing the visual directions of each eye)
-ned patient to see 2 images at the same time

54
Q

what can void a correspondence test

A

image suppression or fusion

55
Q

how can you make the od and os test images unfusible

A

spatial separation
time separation
form separation

56
Q

what is spatial separation

A
  • use polaroid glasses and pol target so each eye sees one image, keep background fusible
  • large vertical disparity maintains dissociation (od image above where they are looking, os image below)
  • horizontal directions are compared
  • not often used in clinic
57
Q

what is time separation

when can this be used

A
  • flicker the image to the right eye then to the lef teye
  • pt can’t fuse the images but can still compare the direction
  • used in “major amblyoscope”
58
Q

what is form separation

when can this be used

A
  • 2 image shapes are so diff they can’t be fused
  • used in afterimage test (horiz in one eye and vert in other, can compare direction of each image) and bagolini lens test (diff orientation in each eye, can’t fuse but cna compare their visual direction)
59
Q

what are the 2 questions you must ask to diagnose ARC

A
  1. where did the patient see the 2 targets?
    - subjective
    - comparison of the visual directions btwn the 2 eyes
  2. where were the images on the retina?
    - are they both on fovea?
    - stimulate foveas monocullary to ensure this
60
Q

what is the afterimage test

A
  • monocularly place afterimage on each fovea
  • open both eyes
  • assess visual directions: cross=foveas have same visual direction and are corres points, no ARC
61
Q

if a vertical line was on the left eye and a horiz line on the right eye, what would a pt with a left esotrope w/ ARC see

A

horiz line to the left and vertical line to the right (crossed diplopia)

  • bc the fovea of the left eye is temporal to the retinal point that is corresponding w/ the fovea of the straight eye
  • afterimage is temporal to the point being used to see “straight ahead” so it will appear in the nasal field
62
Q

if a ptient is strabismic with arc, what would they see with the bagolini lens

A

2 lines form a symmetric cross

63
Q

what would a ptient with strabismus but no arc see with a bagolini lens

A

2 lines that are not overlapping

64
Q

if the patient has a left esotropia what will they see with the bagolini lens

A

bulb and streak stimulate a nasal point on the left eye

  • fovea stim in the right eye
  • left eye will see the image in the temporal field = uncrossed dipolpia
  • botton streaks, no top
65
Q

what is the zero measure point

A

the peripheral retinal point that the fixation target image falls on on the turned eye

66
Q

what is the pseudofovea (pf)

A

the PVD moves from the fovea to a point closer to the zero-measure point in the turned eye

67
Q

in a normal left esotropic eye w/o arc, where would the patient see the image of the target

A

to their left w/ their left eye

-uncrossed dipolopia

68
Q

what will the patient see if the pseudofovea lies on the zero measure point

A

single

69
Q

how are ef and pf related

A

they both use a point other than the fovea as the PVD

  • they are measured separtately bc the brain rewires these btwn binocular and monocular vision
  • may be diff than the
70
Q

when the pseudofovea is shifted from the physiological fovea, all other local signs…

A

shift with it. in the same direction and by the same amount

71
Q

a patient with arc will have a psuedofovea that is closer to the zero measure point, what does this result in

A

smaller amount of disparity, smaler amount of diplopia

-img on the zero ref point seems to be closer to the straight ahead position

72
Q

a patient w/o arc but with the same amount of eye turn of patient w/ arc will use what as their pvd
waht does this mean

A

fovea => thus the fixation image will be stimulated a point far from the fovea => larger diplopia

73
Q

the displacement of the psuedofovea correlates with the size of…

A

the strabismus

74
Q

why can permanent diplopia occur after strab correction surgery

A

patinet is still using arc
-when the ey was turned this accounted for it but now it has a straight eye and the visual directions btwn the eyes are confused

75
Q

what are the 3 types of arc

A

harmonious: single; pf at zero measure point.
unharmonious: uncrossed diplopia=eso, crossed=exo; pf btwn the fovea and zero meausre point
paradoxical: crossed=eso, uncrossed=exo; pf more than the amount of eye turn

76
Q

how many prism dioptoers is arc considered

A

20 prism diopters

77
Q

what is burian’s sensory theory of arc (most widely accepted)

A

arc is a sensory adaptation to constant strabismus

  • deviated local signs are remapped in visual cortex (develops slowly throughout early childhood)
  • do not lose normal corres completely
  • arc can be turned on and off once established
78
Q

what is morgan’s motor theory of arc

A

arc is the result of the registration of the abnormal motor innervation that causes strab

79
Q

what can morgan’s motor theory predict

what can it not easily explain

A

harmonious arc-no fusion or stereo bc the points on the retina do not agree
nonuniform arm

80
Q

how does the motor theory best explain covariation

A

as the amount of the eye turn decreases, the amount of arc should decrease as well.
the amount of arc depends directly on the motor innervations of the eye muscles and the amount of eye turn

OD2-BVOM (6 decks)

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