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Binocular Vision > microtropia - MEH > Flashcards

microtropia - MEH Flashcards

1
Q

define microtropia

A

a constant small angle unilateral strabismus under 10 prism dioptres, presence of subnormal BSV

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2
Q

clinical characteristics of microtropia (7)

A
  • manifest monocular strab 10^ or less
  • anisometropia (commonly hypermetropia)
  • amblyopia (reduced VA in the affected eye)
  • abnormal BSV (reduced stereovision) and sensory and motor fusion
  • may have foveal supression scotoma
  • may have eccentric fixation
  • can have NRC or ARC
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3
Q

can you get a small angle squint without BSV?? and is this a microtropia?

A

NO - main point of a microtropia is that px CAN achieve BSV

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4
Q

what are the 3 main causes of microtropia?

A
  • anisometropia
  • hereditary
  • unknown
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5
Q

what is the most common cause of microtropia?

A

anisometropia

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6
Q

why is anisemotropia a cause of microtropia?

A

results in a defocused image to the more ametropic eye

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7
Q

what is NRC?

A

normal retinal correspondence - you do this with both eyes.
- nasal retina in 1 eye corresponds to temporal retina of the other eye

Nasal corresponding with temporal allows us to have binocular single vision

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8
Q

what is ARC?

A

abnormal retinal correspondence
- sensory adaptation to manifest strabismus to facilitate BSV
- fovea of 1 eye corresponds to an extrafoveal area of the other eye
- This is a binocular condition

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9
Q

Is eccentric fixation binoc or monoc condition?

A

monocular

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10
Q

what is eccentric fixation?

A

the eye fixates with an area outside the fovea

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11
Q

what are the sub classifications of eccentric fixation?

A
  • parafoveal
  • macular
  • paramacular
  • peripheral
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12
Q

do you get EF or ARC in microtropia?

A

can be both - depending on whether the eyes are viewing monoc or binoc

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13
Q

what are the 2 types of microtropia?

A

microtropia WITH identity
microtropia WITHOUT identity

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14
Q

Does the word “identity” refer to fixation or deviation in microtropia?

A

fixation

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15
Q

CT results for microtropia WITH identity

A

no manifest movement noted on cover/uncover

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16
Q

fixation in microtropia WITH identity

A

eccentric fixation = stable parafoveal fixation

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17
Q

in a microtropia WITH identity, what is the amount of eccentricity is equal to?

A

the angle of deviation. For an example if the squint is 6D this relates to 12 degrees ; this is where the eccentric fixation will be

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18
Q

what is the retinal correspondence in someone with a microtropia WITH identity?

A

ARC is present

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19
Q

do you have stereopsis with a microtropia WITH identity

A

gross stereoacuity

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20
Q

why is there no movement seen on cover/uncover in a microtropia WITH identity?

A

px is using parafoveal fixation therefore no change in fixation - they never use their actual fovea to view. The use parafovea binocular and monocularly

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21
Q

in a microtropia WITH identity, how is BSV appreciated?

A

ARC, no diplopia appreciated

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22
Q

CT results of microtropia WITHOUT identity

A

small manifest deviation noted on cover/uncover
large latent component may be noticed on ACT

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23
Q

where is the fixation with someone with microtropia WITHOUT identity

A

central fixation

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24
Q

in a microtropia WITHOUT identity, does eccentric fixation coincide with the angle of deviation?

A

no

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25
Q

retinal correspondence in someone with microtropia WITHOUT identity

A

ARC or NRC with central suppression scotoma

26
Q

in someone with microtropia WITHOUT identity, how do they appreciate BSV? if the px has ARC

A

it will be harmonious ARC, therefore able to achieve BSV
Nr or grey dot corresponds to FI under binoc viewing

27
Q

in someone with microtropia WITHOUT identity, how do they appreciate BSV? if the px has NRC

A

Expansion of panums fusional area

28
Q

what is the secondary classification ?

A

primary and secondary

29
Q

What is primary microtropia?

A
  1. Initial defect
  2. accompany other concomitant deviations
30
Q

what are 2 types of secondary microtropia?

A

residual
seen after stabismus surgery ; such as surgery after infantile esotropia. We correct the esotropia to a microtropia

31
Q

what are the 2 aims of investigation?

A
  • diagnose the microtropia
  • assess the quality of BSV (stereo and fusion)
32
Q

how do the majority of px’s present with a microtropia?

A
  • referred from failed vision screening (school or pre-school_
  • referral from routine eye exam with defective vision
  • constant or intermittent squint
33
Q

why is family history important?

A

hereditary factor for microtropia

34
Q

what does the vision vary from in microtropia?

A

0.2 to over 1.00 LogMAR

35
Q

why do you need to use crowding when testing VA?

A

most accurate vision with crowded linear chart compared to single optotypes ; this is more real world viewing

36
Q

what is affected when VA is affected?

A

speed of reading letters

37
Q

what will the cover test look like with px with identity?

A

They will no manifest devation on cover, uncover . but may have latent on alternating cover test

38
Q

What will the CT look like for a px without identity?

A

They will have a small manifest devaiton, less then 10 dioptres. They may appear to have a larger compenetn on alternating CT.

39
Q

how do you assess sensory fusion?

A

bagolini lenses and worth’s lights

40
Q

what is wrong with using worth’s lights > bagolini lenses?

A

WL is difficult to show suppression scotoma/central suppression

41
Q

how do you assess motor fusion?

A

20^BO and PFR

42
Q

what does motor fusion tell you about a heterophoria?

A

indicates how well compensated the hetereophoria is

43
Q

is there stereoacuity in someone with microtropia?

A

reduced - RARELY stereoblind

44
Q

what test is stereovision harder with?

A

random dot stereogram as they do not have bifoveal fixation

45
Q

how do you assess fixation?

A

use ophthalmoscope/visuscope
- have px fix on centre of target
- cover px’s non-fixing eye
- comment on location of fixation as well as if the fixation is steady or wandering

46
Q

what is normal retinal correspondence also knwon as?

A

bifoveal fixation

47
Q

how does the 4^BO test workin px with bifoveal fixation (normal)?

A
  1. prism place in front of RE - image is displaced away from fovea RE adducts to maintain fixation
  2. LE moves (herrings law) as image to LE falls on temporal retina and projects nasally resulting in dip
  3. diplopia causes nasal movement of LE to maintain BSV
48
Q

how does 4^BO work (in left microtropia)

A
  1. prism placed in front of RE - image is displaced away from fovea RE adducts to maintain fixation
  2. left eye moves out (herrings law), image to the LE now falls within the supression scotoma resulting in NO diplopia response
  3. prism placed in front of LE, image falls within the suppression scotoma so there is NO movement of EE seen
49
Q

what do you write down if you have carried out 4^BO test and they DONT have a microtropia?

A

4^: bifoveal fixation

50
Q

what do you write down if you have carried out 4^BO test and they DO have a microtropia?

A

4^: +ve supression scotoma (L/R)

51
Q

main management:

A

optimise VA

52
Q

how do you optimise VA?

A
  • cyclo
  • glasses worn full time for full refractive period (16-22 weeks)
  • part time total occlusion prescribed - cease once no further imporvement for VA
  • continually monitor fixation/supression throughout treatment
53
Q

what is the interocular difference often seen between the eyes?

A

0.1-0.3 logMAR

54
Q

what 3 factors have a great baring on visual outcome?

A
  • fixation
  • degree of anisemotropia
  • compliance
55
Q

is there a difference between how you treat WITH and WITHOUT identity?

A

no

56
Q

what do majority of microtropic px’s have?

A

anisemotropia

57
Q

what does identity relate to?

A

fixation rather than cover test findings

58
Q

When do you start occlusion therapy?

A

After 16-22 Weeks, if the vision has not improved. When occluding we will neeed to monitor their fixation and suppression throughout their treatment

59
Q

When a young px has come in with anismetropia what do we do?

A

We will need to give them the correction then see them in 16-22 weeks - if visions still shit then refer for occlusion

60
Q

what is the normal diffrence between eyes?

A

0.1 - 0.3

61
Q

If the vision has not improved what is important to let the parents know?

A

The child will need to wear full time and probs will not grow out of them

62
Q

what we treat after the age of 7?

A

Sometimes with anismetropia and microtropia we can sometimes treat them

Binocular Vision (30 decks)

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