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OV2018 binocular vision > introduction to binocular vision > Flashcards

introduction to binocular vision Flashcards

1
Q

what is binocular single vision (BSV)?

A

. when looking at an object , you can see it with both eyes but you don’t see two images
. simultaneous use of two eyes to give one mental image

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2
Q

why doesn’t the object appear as two when using both eyes to look at it ?

A

because in the cortex, they confuse the image from the right and left eye together into one single image

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3
Q

what happens if you do not have binocular single vision (BSV)?

A

. you will see double

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4
Q

why do we have 2 eyes?

A

. spare eye ( incase one has a pathology?

. wide field of view

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5
Q

what are the advantages of BSV? both eyes working together

A
  1. binocular summation- enhanced visual acuity, contrast sensitivity and motion
  2. ability to perceive depth - stereopsis
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6
Q

what is stereopsis?

A

. ability to perceive depth

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7
Q

what do you need to develop normal BSV?

A

. you need normal retinal correspondence (NRC)

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8
Q

what is normal retinal correspondence (NRC) ?

A

. every point on the retina corresponds to a certain point in space

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9
Q

how does every point in the retina correspond to a certain point in space in the left eye?

A

. nasal retina corresponds to temporal visual field
. temporal retina corresponds to nasal visual field
. superior retina corresponds to superior visual field and inferior retina corresponds to superior visual field

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10
Q

how does normal retinal correspondence work in binocular condition (in 2 eyes)?

A

. the fovea of the right and left eye are exactly corresponding
. this allows the patient to see the point in space as single image.
. temporal retina of right eye corresponds to nasal retina of left eye
. nasal retina of right eye corresponds to temporal retina of left eye

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11
Q

what are cortical ( cyclopean projection ) in NRC used to describe?

A

used to describe BSV

-imaginary eye of what the px would see in the cortex when they put the image of the right and left eye together

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12
Q

what is theoretical horopter?

A

. objects stimulating exactly corresponding retinal points lie on an imaginary line called the horopter and are see as single

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13
Q

explain the vieth-muller circle?

A

. every single point lying on the vieth-muller circle would stimulate exactly corresponding retinal points in the eyes and therefore every point in the circle will be seen as single

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14
Q

what is the vieth-muller circle?

A

. the theoretical / geometrical horopter in the horizontal plane has come to be known as the vieth-muller circle

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15
Q

what happens to those objects not lying exactly on the horopter but very close to it?

A

. the objects will still be seen as single as they were almost corresponding objects , this will allow us to see in 3D- allows to see stereopsis

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16
Q

what happens if an object does not stimulate exactly corresponding areas?

A

. there is a small area around the horopter in which corresponding and almost corresponding objects are still seen singly
. this is known as panums fusional space

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17
Q

what is panums fusional space?

A

. it is the disparity of the almost corresponding points which are fused into one single image and results in stereopsis

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18
Q

what happens when objects fall outside panums area?

A

. all objects outside panum’s fusional space give rise to physiological (normal) diplopia
. this type of diplopia exists when you have binocular vision ( it is normal)

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19
Q

what give rise to diplopia?

A

. when points on the retina do not correspond

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20
Q

what type of double vision will you see when looking at the flowers in front of the tree?

A

. the flowers stimulate temporal foveas in both eyes- which means they will see double.
. temporal retina projects nasally
. image on the right stimulated from left eye
. image of left stimulated from right eye
. this give crossed physiological diplopia

21
Q

what is crossed physiological diplopia?

A

. image on the right stimulated from left eye

. image of left stimulated from right eye

22
Q

what is uncrossed physiological diplopia?

A

. image on the left stimulated from left eye

. image on the right stimulated from right eye

23
Q

what are the grades of B.S.V?

A

. worths grades

24
Q

what are worths grades?

A
  1. simultaneous perception
  2. fusion
    - sensory fusion
    - motor fusion
  3. stereopsis

. the more of these they have the better the B.S.V is

25
Q

what is simultaneous perception?

A

ability to perceive two images simultaneously, one from each retina

26
Q

what is sensory fusion?

A

. you can see an object with the right and the left eye and in the visual cortex you confuse that together into one image

. integration of two similar images, one formed on each retina into one image within the brain
. images must be similar in brightness, size and form in order to fuse them together

27
Q

what is motor fusion?

A

. ability to maintain sensory fusion through a range of vergence szmovements

28
Q

what is stereopsis?

A

. the perception of relative depth of objects by the fusion of relative disparity of images from the two eyes

e. g magic eye picture seen- so if you were to look directly you would use fovea of right and left eye and that was stimulate exactly corresponding retinal points and you would not be able to see in depth in fact the image will be flat.
- So need to stimulate almost corresponding retinal points by looking behind magic eye pic or infront - this will allow this= and the fusion of the slightly different images to then see in depth.

29
Q

what happens when one of your eye turns ( strabismus )?

A

you need to find out which of the following your patient has
. confusion-normal retinal correspondence (NRC)
. diplopia ( NRC)
. suppression ( NRC )
. abnormal retinal correspondence

30
Q

how do normal eyes behave?

A

. fovea of right eye corresponds with fovea of left eye
. nasal retina of right eye corresponds with temporal retina of left eye
. temporal retina of right eye correspond to nasal elements of the left eye

31
Q

what happens when one of your eye turns ( strabismus )?- not likely

A

. the fovea of the fixating left eye (FLE) receives the image of the fixated image ( tree ) and the fovea of the strabismic right eye receives a different image ( flower )
. the two images are superimposed
. this causes confusion (NRC)

32
Q

what is more likely to happens when one of your eye turns ( strabismus )?

A

. pathological diplopia
. the patients has a fixating left eye
. the patient has FRE
. the tree is falling on nasal retina instead of fovea
. nasal retina always projects temporally
. the tree they see with right eye, they will see it on the right hand side giving them uncrossed double vision

33
Q

what is pathological diplopia?

A

. inability to fuse corresponding foveal images
. occurs in manifest strabismus when the fovea of the fixated object stimulates a non-corresponding peripheral area in the strabismic eye

34
Q

what happens if child was to develop a strabismus?

A

. when both eyes are open the cortex ignores the image on the eye with esotropia

35
Q

what is suppression?

A

. mental inhibition of the image in front of eye which is deviated off when both eyes are open
. only happens with both eyes open
children who suppress usually do not have stereopsis

36
Q

what happens if you cover the left eye and use the esotropic left eye?

A

. the child will use the fovea of left eye

37
Q

what happens if a child develops a constant small angle strabismus ?

A

. this is called abnormal retinal correspondence

38
Q

what is abnormal retinal correspondence?

A

. when looking at an object
. the fovea hits the tree with LE
. the tree hits the pseudo fovea of RE
. the brain has re-wired to use the pseudo fovea
. therefore only one object is seen
. overcomes diplopia and confusion
. you will have abnormal binocular single vision

39
Q

what is abnormal binocular single vision useful to have?

A

. you will have a form of stereopsis

. you will have a form of binocular summation

40
Q

what happens in a patient with abnormal retinal correspondence if you cover one eye?

A

. when the fixated eye is covered
. the esotropic eye will move outwards to use its fovea as it only exists under binocular conditions ( when both eyes are open)

41
Q

what happens if a patient under 8 develops a manifest strabismus?

A

. the patient will either experience suppression or abnormal retinal correspondence - usually leave alone

42
Q

when do we usually treat strabismus in children under 8?

A

. if they got a large angle and suppression
. suppression treat for cosmesis

. ARC usually don’t treat

43
Q

what happens if an adult patient develops strabismus ?

A

. they will develop confusion or diplopia

. usually teat with prisms, lenses , surgery

44
Q

what is esotropia associated with ?

A

uncrossed diplopia

45
Q

what is exotropia associated with ?

A

crossed diplopia

46
Q

what will a 50 year old with a recent onset constant right esotropia experience ?

A

uncrossed diplopia

47
Q

what is the likely management of six year old girl with moderate right esotropia since early childhood?

A

. likely to have either

  • ARC
  • Suppression

ARC- leave alone
suppression - consider surgery for cosmesis

48
Q

how would you explain suppresion to a child ?

A

. both eyes are working, but not together
. when both eyes are open she either uses her right eye to see or her left
. she does not use them both at the same time
. find activities to judge distance of objects harder

49
Q

What happens if you cover one eye. Will you have any stereopsis if you cover one eye ?

A

no, which is why ARC is a binocular not monocular condition.

OV2018 binocular vision (15 decks)

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