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Optometry class OP2501 > Binocular Vision > Flashcards

Binocular Vision Flashcards

1
Q

what are the 3 levels of binocular vision?

A

-simultaneous perception
-fusion
-stereopsis

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2
Q

what is the simultaneous perception of binocular vision?

A

where both eyes contribute towards visual perception, whether
the images from each eye are combined into a single percept or not.

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3
Q

what is the fusion component of binocular vision?

A

where two images are fused, resulting in a single percept

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4
Q

what is stereopsis part of binocular vision

A

depth of perception of the fusion

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5
Q

what are the advantages of binocular vision?

A
  • Increases field of view
  • Compensates for physiological blind spot
  • Binocular summation
  • Stereopsis
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6
Q

what are symptoms that may indicate binocular vision problems?

A

-diplopia
-asthenopic symptoms
-blurred vision
-for young children: rubbing eyes, avoiding certain types of visual tasks e.c.t

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7
Q

when may you need to follow up diplopia?

A

if its monocular as that could indicate more serious pathology

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8
Q

what is the smallest prism D you can see with cover test?

A

2D and that is barely visible

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9
Q

how can you measure the size of deviation in cover test?

A

by doing prism cover test - Keep changing prisms as you do alternating cover tests until you no longer see the eye deviation.

The base goes in the opposite direction of deviation so exophoria needs correction with base IN prism and vice versa

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10
Q

why are you less likely to use maddox rod and wing?

A

-eyes are completely dissociated
-There is a lot of accommodation happening in maddox rod
-Maddox wing is a fixed distance which may not be the patient’s reading distance

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11
Q

whats the link between accommodation and convergence?

A

increased accommodation results in increased convergence

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12
Q

what kind of deviation is triggered by uncorrected hyperopia?

A

eso deviation as Px accommodates more

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13
Q

what kind of deviation is triggered by uncorrected myopia

A

exo deviation as Px accommodates less at near

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14
Q

What is fixation disparity?

A

where there’s a small amount of misalignment of the eyes when they’re being used binocularly after one of them’s been occluded

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15
Q

when correcting a deviation, which way does the prism go?

A

base of the prism goes opposite to the direction of the deviating eye so exo deviation prism is base IN

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16
Q

what could each of the following scenarios mean?
-more exo at distance than near?
-more eso at distance than near?
-more exo at near than distance?
-more eso at near than at distance?

A
  • More exo at distance than near = divergence excess?
  • More eso distance than near = divergence insufficiency?
  • More exo at near than distance = convergence insufficiency?
  • More eso at near than distance = convergence excess?
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17
Q

what do you record for cover test?

A

-size
-recovery for phorias
-type of deviation
-laterality for tropias (alternating?)
or
-nmd

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18
Q

how does mallet unit to assess fixation disparity work?

A

when the bottom line moves towards the right eye and the top moves towards the left eye, it is an uncrossed and so eso deviation. If the bottom line moves towards the left and the top line moves towards the right, then its crossed = exo deviation. If the lines are in line with each other and the middle of the X, then no fixation disparity is present

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19
Q

What are some of the symptoms involved in asthenopia?

A

-ocular fatigue
-discomfort
-lacrimation
-headaches

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20
Q

what kind of patients should you not use mallet unit on?

A

-those with va worse than 6/12 in each eye
-suppression / amblyopia

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21
Q

which vergence component are you assessing in cover test?

A

fusional vergence

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22
Q

which component of BV is the highest form?

A

stereopsis

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23
Q

what is the contralateral antagonist of the left medial rectus

A

the right medial rectus

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24
Q

what is confusion?

A

when a patient can see two images superimposed on top of each other making it hard to work out what they’re seeing

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25
Q

what is impaired laevoversion?

A

when movement of both eyes to the left is abnormal

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26
Q

what is movement of both eyes to the right called?

A

dextroversion

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27
Q

what does listing’s law suggest?

A

the eye has a centre of rotation at which it moves

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28
Q

what are the 3 axes of fick?

A
  • Y axis is the optical axis - does straight through the pupil = cyclorotation so twists in and out
  • X axis lies horizontally = vertical rotation so up and down
  • Z axis lies vertically = horizontal rotation so left and right
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29
Q

how can you tell in a CT scan if the eyes are dissociated?

A

If the Y axis are not pointing in the same direction

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30
Q

what are the 3 positions of gaze?

A

-Primary = straight ahead
-Secondary = up/down/left/ right
-tertiary = combo e.g. up and right

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31
Q

what does donder’s law suggest?

A

Ocular orientation required to look at a particular point in space is always the same and independent of the previous ocular position

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32
Q

what are agonist and antagonistic muscles?

A

-Agnostic muscles are eye muscles that work in a pair to move the eyes to look in the same direction
-Antagonistic muscles are muscles that oppose the agonist muscles

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33
Q

what is sherrington’s reciprocal law of innervation?

A

where one muscle of the eyeball contracts so the opposite muscle has to relax

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34
Q

what does herring’s law suggest?

A

contralateral agonists move with equal innervation.

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35
Q

what are the two types of binocular movements?

A

-vergences (oppostive, disjunctive)
-Versions (same direction, conjugate)

36
Q

look at types of versions and vergences screenshot

A

ok

37
Q

what is the most basic form of binocular visiom?

A

simultaneous perception - seeing an object with both eyes - may or may not be combined into one single precept

38
Q

what is the main part of BV you want patients to achieve?

A

steriopsis - depth of perception because its the highest form of BV

39
Q

where does processing of BV occur?

A

in the brain NOT THE RETINA

40
Q

how is binocular vision processed?

A
  1. info enters from separate points in our visual field in each eye
  2. info gets crossed when the nerve fibres cross at the optic chiasm
  3. visual cortex can then process the info as one image
41
Q

what does localisation help us do?

A

helps us understand where objects are in our visual field

42
Q

what are the two types of localisation?

A

-Oculocentric localisation is seeing objects where they are in relation to each other
-Egocentric localisation is seeing where objects are in relation to you using your eyes and other proprioceptive cues

43
Q

what are images in the secondary visual direction?

A

images that fall on the retina but do not fall on the fovea

44
Q

what is the difference between images in the primary and secondary visual direction

A

primary fall on the fovea whereas secondary fall outside of the fovea elsewhere on the retina

45
Q

why might we see two objects as superimposing eachother?

A

as they are both on the same visual direction

46
Q

how does an image fall on corresponding points on the retina?

A

as visual angles of each point subtend to equal points on the retina on both eyes when using both eyes to look at an image

47
Q

what does an image on corresponding points on the retina of the right and left eye mean for the image?

A

the two images on each retina get perceived as a single image

48
Q

what is retinal disparity?

A

where images between the right and left eye change when you look at objects that appear to be behind each other when looking at them binocularly

49
Q

what is physiological diplopia?

A

where there’s two images on the same visual axis. the one behind gets seen as diplopic by the cyclopian eye

50
Q

how do we get over physiological dipolopia?

A

We do not perceive images as diplopic because our brains suppress the image (non-dominant eye usually suppressed)

51
Q

what is a horopter?

A

an imaginary plane for a fixation point where all points along this plane fall on corresponding retinal points so all objects on the horopter are perceived as single

52
Q

what is panum’s area?

A

a region behind and in front of the horopter where objects that are close but do not fall on the same corresponding points but the brain can still fuse the images and compare them to build information about the depth

objects perceived as single but with depth

53
Q

what do objects that dont lie on the horopter or in panum’s area appear as?

A

double

54
Q

when can BV problems arise?

A

-at birth or within first 6 months = CONGENITAL/ INFANTILE
=pre school/ early school = EARLY CHILDHOOD
-any other time due to e.g. trauma, cranial nerve palsy or decompensation = ACQUIRED IN LIFE

55
Q

give 9 causes of BV problems

A

-neurogenic
-myogenic
-refractive/accommodative
-developmental
-congenital
-systematic disease
-environmental
-latrogenic
-idiopathic

56
Q

give 12 types of BV problems

A

-heterotropia
-heterophoria
-ocular motility
-accommodation problems
-fusional vergence problems
-amblyopia/ suppression
-abnormal retinal correspondence
-aniseikonia
-fixation disparity
-microtropia
-nystagmus

57
Q

What is the motor aspect of BV?

A

the ability of the muscles to move the eyes accurately - motor dysfunction results in loss of fixation disparity due to deficiency in the brain

58
Q

what is the sensory aspect of BV?

A

how the brain uses signals sent from the retina of each eye combined to produce a visual precept which includes stereopsis

59
Q

what tests can you do to assess motor function in BV?

A

-cover test
-ocular motility
-NPC
-maddox rod/wing/double
-vergence facility and jump convergence
-fusional reserves
-Hirschberg &
Krimsky
-prism reflex test
-fixatio disparity

60
Q

what tests can you do to assess sensory function of BV?

A

-check VA
-fixation disparity
-stereopsis tests
-suppression tests

61
Q

what are glasses with a line on them?

A

bifocals

62
Q

what could cause monocular diplopia?

A

keratoconus

63
Q

how much phoria is normal at near and distance for most people?

A

Normal phoria at near for most people is 3 prism diopters exophoria and for distance is 1 diopter exophoria. This is just a guide though as some people have much higher phorias and manage well as well some some people having even smaller phorias and not managing well

64
Q

what does it mean if near vision is worse binocularly compared to monocularly

A

they most probably have a BV issue

65
Q

what is a convergence excess deviation?

A

a deviation that is greater at near fixation target than at distance

66
Q

patients that ae found to be hyperopic with no prescription what is it possible to also find?

A

a large esophoria

67
Q

when may you only measure AoA monocularly?

A

when you find the NPC to be low because you expect the AoA to be closer to the eye than NPC

68
Q

what is the AC/A ratio?

A

(accommodative convergence/ accommodation) the accommodative convergence per dioptre of convergence for horizontal movements only (vertical movements do not affect accommodation)

69
Q

what might suggest a patient has a high AC/A ratio?

A

If you have a patient that is much more exo or eso at near than distance on cover test

70
Q

What are the 4 components of accommodation?

A

-tonic
-reflex
-vergence
-proximal

71
Q

what is tonic accommodation?

A

*Resting state i.e. there is no stimulus.
* Usually between 0.00D and 2.00D, mean 1.00D in young
adults

72
Q

what is reflex accommodation?

A
  • The automatic response of accommodation to maintain a
    clear retinal image.
  • Stimulus is small amounts of retinal blur: <2.00 D.
73
Q

what is vergence accommodation?

A
  • Stimulus is convergence.
  • Only present when both eyes open
  • Contributes to increase in amplitude of accom. when binoc
    cf. monoc
74
Q

what is proximal accommodation?

A

Stimulus is the perception of the proximity of the fixation
target

75
Q

what is the NPC?

A

the nearest point which can be converged upon and is generally considered adequate if it’s closer than 10cm

76
Q

what is the definition of convergence?

A

equal adduction of each eye to a point closer than infinity

77
Q

when is convergence symmetrical and asymmetrical?

A

if the eyes are adducting on the saggital plane then convergence is symmetrical and if not then it’s asymmetrical

78
Q

what combo of movements allows for asymmetrical convergence?

A

a combination of symmetrical vergence and version movements

79
Q

Why is AC/A good to measure?

A

-predicts the change in vergence that a change in accommodation will elicit
-a high AC/A ratio is associated with certain types of esotropia

80
Q

How do you calculate the AC/A ratio gradient?

A

1.find the patients phoria with and without their prescription
2. find the difference
3. divide this by their Rx

difference in phoria/ difference in accommodative demand

81
Q

how do patients overcome phorias?

A

with fusional vergence and as it cannot work at max all the time, they need to keep some in reserve and poor fusional reserves can cause BV problems

82
Q

what happens when there are negative fusional reserves and you start to increase prism more than needed

A

-when a larger prism is introduced, Limit of fusional reserves reached; eyes start to accommodate to increase convergence and maintain BSV; accommodation makes target blurred but BSV maintained
-when an even larger prism is introduced, Eye can no longer overcome deviation (fusional reserves exhausted) and BSV no longer possible

83
Q

what do base in (negative) fusional reserves assess?

A

the ability of the eye to rotate outwards (from having been turned in due to esophoria) to achieve fusion when removing the cover in cover test

84
Q

what do fusional reserves assess?

A

the range over which you can fuse images

85
Q

look at plotting fusional reserves graph

A

check bv2 powerpoint slides 49-58

86
Q

How can you correct inadequate fusional reserves?

A

prescribe a prism based on fusional reserves

87
Q

What is blurred vision a common symptom of?

A

heterophoria

Optometry class OP2501 (14 decks)

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