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Binocular vision YR 3 > Microtropia > Flashcards

Microtropia Flashcards

1
Q

what is the definition of microtropia and what do patients who got microtropia usually have

A

Unilateral small angle strabismus (10∆ or less)

Binocular single vision(BSV) with abnormal retinal correspondence develops (ARC)

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2
Q

what does 10∆ correlate to in degrees

A

5-8 degrees

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3
Q

list 6 features of microtropia

A
  • Anisometropia: usually astigmatic or hyperopic and other eye plano
  • Foveal suppression scotoma
  • Amblyopia: as not fixing on best part of fovea
  • Eccentric fixation: does not fix with fovea, but slightly less centrally
  • Reduced fusional amplitudes: compared to what a non-microtropia px has
  • Subnormal stereopsis: compared to what a non-microtropia px has
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4
Q

what type of amblyopia does a microtropia px usually have

A

usually astigmatic or hyperopic and other eye plano

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5
Q

why do patients with microtropia tend to have amblyopia

A

as not fixing on best part of fovea

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6
Q

what 2 things does a microtropia px have less of in comparison to a normal px

A
  • fusional amplitudes
  • stereopsis

these are still present in a microtropia px, but to a lesser extent

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7
Q

what is the prevalence of microtropia out of all squints

A

2.84% seen in general practice

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8
Q

which direction of microtropia is more common than which and which direction is generally more rarer

A

Micro ET (more common) > XT (less common)

Vertical microtropia rare (no variability in size of squint)

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9
Q

microtropia is _________ throughout life

A

microtropia is constant throughout life

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10
Q

what is the aetiology of microtropia thought to be

A

Most common theory:
Anisometropia - Hyperopic +/- astigmatism

because they have anisometropia, they go on to develop microtropia

however microtropia is also thought to cause anisometropia, because the microtropic pc has effective vision from a squint which results in anisometropia

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11
Q

what does anisometropia result in

A

Results in a defocused image to the more ametropic eye. As fixation reflex not fully developed patient uses a retinal point other than the fovea to fix (pseudo fovea)

the patient always accommodates to the least ametropic eye e.g. if its the right eye, then thats the eye that will govern the accommodation and if the left eye is hyperopic, then it will always be out of focus

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12
Q

what 4 things could the result of anisometropia explain about microtropia

A

This could explain:

  • Foveal suppression scotoma
  • Amblyopia
  • Eccentric fixation on border of scotoma
  • ARC with reduced fusion, defective stereopsis
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13
Q

what type of visual acuity does a person with microtropia have as a result of eccentric fixation on the border of the scotoma

A

6/7.5 or 6/9

as its very close to the fovea

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14
Q

what type of condition is abnormal retinal correspondence ARC and what is it defined as

A

ARC is a BINOCULAR condition: it only happens when both eyes are open and is not there is using each eye individually i.e. if you cover the straight eye, the other eye won’t have ARC anymore and will use the fovea for fixation

The fovea of 1 eye corresponds to a non-foveal area in the other (squinting) eye

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15
Q

what is microtropia the most comm form of
what does it allow
what does it ensure

A

Microtropia the most common form of ARC
allows binocular vision (i.e. allows fusion and stereopsis to develop)
ensures long-term stability of the alignment of the squint

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16
Q

what type of condition is eccentric fixation EF and what is it defined as

A

EF is a UNIOCULAR condition: if you cover up the straight eye, the other eye will stay fixing with their eccentric point

There is fixation of an object by a point other than the fovea

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17
Q

what is seeing someone with an eccentric fixation relevant in

A

differentiating between micro with and without identity

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18
Q

what 2 things may co-exist in microtropia and explain how

A

ARC and EF may co-exist in microtropia

fix with different point on retina when affected eye viewing monocularly and binocularly

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19
Q

explain the 2 things that can happen with a micro tropic patient’s foveal suppression scotoma when you cover the right eye

A
  • when cover the right eye, the px will re-fixate and uses the left eye’s fovea, so they use that point binocularly to get ARC

or

  • when cover the right eye, the left eye stays there at the same place and uses that point as their pseudo fovea eccentrically fixing
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20
Q

what are the 2 classifications of a primary mictrotropia and what are they based on the outcome of

A
  • with identity
  • without identity

based on the outcome of a cover test

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21
Q

what is seen in a ‘with identity’ microtropia px

A

NO manifest deviation
heterophoria may be present

i.e. px is using their eccentric point/pseudo fovea binocularly and uniocularly = don’t see any deviation on cover test

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22
Q

what is seen in a ‘without identity’ microtropia px

A

Small constant manifest deviation
May be associated heterophoria with partial recovery to microtropia angle

i.e. will see a small convergent flick, when you do a CT, cover the fixing eye and you will go to the true fovea on CT

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23
Q

what are the 3 aims of investigating a microtropia

A
  • Diagnose the microtropia
  • Assess quality of binocular single vision
    fusion
    stereopsis
  • Differentiate from bifoveal fixation
    Anisometropic amblyopia
24
Q

why is it important to assess quality of binocular single vision when investigating someone with a microtropia

A

because a px with poor fusion and stereopsis means they’re more likely to decompensate to bigger squints

25
Q

why is it important to differentiate from bi foveal fixation when investigating someone with a microtropia

A

it makes a difference to what you expect to get for your end result treatment
treatment is the same but when you stop will differ depending on whether they have got true bifocal fixation or if they fixate with a extra foveal point in the other eye

26
Q

give 3 possible causes (history) for a patient to visit you and are found to have a microtropia

A
  • Referred with defective vision in one eye
    School nurse check (4.5 years of age)
  • May present with constant or intermittent squint (without glasses)
    Less common reason
    Px will have a bigger squint than 10^, you then do a cyclo refraction and prescribe glasses for hypertropia and px ends up with a microtropia
    Sometimes presents as adults
  • Occasionally present to A and E because child says cannot see out of one eye
27
Q

what is found and prescribed to a px with microtropia during refraction and fundus check

A

Anisometropia
Hypermetropic with or without astigmatism

Glasses for full-time wear:
can give plano in the fixing eye and hyperopic correction in micro tropic eye, but if theres a lot of refractive error in the fixing/least ametropic eye, then they will have to be corrected
there is a lot of improvement with glasses on most patients, but child may not find a big improvement with glasses, but they must wear them

Review 2/12 (6-8 weeks) to check vision (if it has improved) and decide on future management

28
Q

what is the pre treatment vision of a micro tropic patient
which type of test is best to use when measuring visual acuity and why
what is the optimum vision in the micro tropic eye

A

Pre-treatment vision varies
6/60 to 6/9

Beware crowding phenomenon - so move onto crowded visual acuity test as soon as possible as uncrowded over estimates the visual acuity
linear charts rather than single optotypes to detect small differences in visual acuity
ensure child not peeping!

Optimum vision in the microtropic eye is about 1 line lower than better eye
(as not fixing with the true fovea)

29
Q

name 7 occupations you can do if visual acuity is no worse than 6/12 in the worse eye

A
  • Police Officer / prison officer
  • Fire Officer
  • Train driver
  • Guard
  • Emergency or depot driver
  • Passenger carrier i.e. taxi
  • HGV driver
30
Q

name 2 occupations you can do if visual acuity is no worse than 6/9 in the worse eye

A
  • Commercial pilot

- Air traffic Controller

31
Q

name an occupation you can do if visual acuity is no worse than 6/6 in the worse eye

A

Motor sport

32
Q

what is seen in Microtropia with identity when you occlude the right eye and what is explained by this
what 3 things are identical in Microtropia with identity and why

A

No manifest deviation on cover test
RE occluded, LE fixates with Pl – parafoveal fixation with same retinal area under binocular and monocular viewing
(no manifest deviation on cover test, may see a phoria)

Absence of manifest deviation is explained by presence of stable parafoveal fixation

Angle of deviation
Angle of eccentricity
Angle of anomaly
= all identical

Because it is the same point they use i.e. ARC and absolute eccentric fixation point coincide with angle of squint

33
Q

up to what age will you see a successful microtropia treatment

A

in children up to 17 years old

34
Q

what is seen in microtropia without identity when you occlude the right eye and why

A

Small manifest deviation seen on cover test
RE occluded, LE moves and fixates with retinal area between Nl and F and minimal ET seen on cover test as monocular fixation taken up.

because eccentric fixation does not coincide with angle of squint in monocular and binocular conditions

35
Q

list 4 things you want to measure when investigating a micro tropic patient’s binocular status and give examples of which tests you can use to carry them out
which 3 of these are the same for with and without identity

A
  • Sensory fusion
    Bagolini glasses
  • Quality of motor fusion
    Prism fusion range
  • Stereopsis
    TNO, Wirt, Frisby

= Same for with and without identity:

  • Measurement of deviation
    Prism cover test / simultaneous prism cover test

= Different for with and without identity

36
Q

which 3 forms of binocular status is the same for with and without identity microtropia

A
  • Sensory fusion
  • Quality of motor fusion
  • Stereopsis
37
Q

describe how bagolini glasses are used to test sensory fusion and what a microtropia px will see and why

A
  • Patient fixes light 1/3m or 6m away (sensory fusion)
  • As lenses have small striations (at right angles to each other), a white line is seen crossing through the light
  • Minimal dissociation as aware peripheral objects surrounding light
  • Ask patient to draw what they see
  • Microtropia patients may on questioning report a gap in the cross at the centre because of the parafoveal suppressing area ~5 deg
  • Difficult for patient to see
  • Does not assess motor fusion only sensory fusion
38
Q

what does measuring prism fusion range assess in a micro tropic px
what should you check when doing it and what should you find what else may be required and why before deciding to treat
how should you check your results on a child

A
  • Assessment of motor fusion
  • Check BO and BI range
    often reduced level
  • Control such as Bagolini glasses may be required to confirm when fusion is lost as patient suppresses at break of fusion
    This is essential as you can decide to patch that child without breaking their fusion

You have to check the patient’s fusion objectively as a child won’t tell you when they have diplopia

39
Q

what test is used to measure the amount of deviation in a microtropic px
what does this test require
what 2 types of angle is this test used to measure
and what is this test used to differentiate

A
  • Prism Cover Test (PCT) (as to have a microtropia, they have to have 10^ or less)
  • Requires good cooperation (e.g. not helpful if VA is poor)
  • Used to measure latent or manifest angle
  • Microtropia with and without identity
40
Q

what are the stereo results like in a micro tropic patient
in which type of stereo test is there difficulty obtaining a response from and give 2 examples
which type of stereo test do they tend to do better in and give an example

A

Often reduced

have difficulty obtaining response from pure random dot tests
e.g. Lang and TNO

do better in something with better contour
e.g. titmus fly

41
Q

what is a stereo test result NOT an indication of

A

NOT an indication of fusion

42
Q 
list the results found from: 
Refraction
Visual acuity
Cover test
OM
PFR/Stereo
4^ test
Fixation

in microtropia with identity and without identity

A
  • Refraction:
    with = Anisometropia
    without = Anisometropia
  • Visual acuity:
    with = 6/60 to 6/9
    without = 6/60 to 6/9
  • Cover test:
    with = Phoria
    without = Tropia
  • OM:
    with = Full
    without = Full
  • PFR/Stereo:
    with = Reduced
    without = Reduced
  • 4^ test:
    with = Negative for bifoveal fixation
    without = N/A as already manifest squint
  • Fixation:
    with = Parafoveal
    without = N/A as already manifest squint
43
Q

for a patient who had microtropia with identity, how can you prove their reduced vision is due to microtropia and not any other cause

A

Prove there is foveal suppression by assessing

  • eccentric fixation
  • 4∆ prism test

If you got a patient with reduced VA in one eye with defective stereopsis and fusion range, but can’t see anything on CT, then you will know they have a microtropia with a central suppression area by using a 4^ or by looking with an ophthalmoscope for eccentric fixation

44
Q

how must the ophthalmoscope be set up to check for eccentric fixation in a patient who may have with identity microtropia

A
  • light turned to green

- fixation target displayed

45
Q

list the steps of how you will carry out the assessment of eccentric fixation on a with identity microtropia px

A
  • Undertake in dark room, patient may need to be dilated
  • Check good eye first to assess understanding & cooperation
  • Examiner projects the fixation target onto the fundus close to the fovea
  • Patient is instructed to look directly at the centre of the circle
  • Note the position of the fixation target on the fundus
  • There is a decrease in visual acuity with increasing distance from the fovea
46
Q

what results may you see in a px with eccentric fixation from testing it with an ophthalmoscope and which values show that the patient does not have microtropia

A

1 = Parafoveolar
2 = Parafoveal
3 and 4 = Peripheral: Not seen with microtropia

47
Q

what is the 4^ test used for
what type of test is it
what must the patient fixate on whilst being tested

A
  • Shows if patient has foveal suppression
    i. e. microtropia with identity
  • Objective test
  • Fixate on small detailed target (and nothing around it e.g. a small spot in the distance on snellen chart or small house on budgie stick)
48
Q

describe what will be the normal bifoveal response from a 4^ BO test if placed in front of right eye

A

4Δ BO (if eso) Prism infront of RE/fixing eye, therefore image displaced away from fovea, RE adducts to maintain fixation (so will see movement of eye under prism, towards the apex of the prism)

Due to Herrings Law, LE also moves. Now in LE image from letter falls on temporal retina and projects nasally resulting in diplopia

Diplopia simulates nasal movement of LE to maintain BSV. This is the observed movement of the prism being overcome.

49
Q

describe what will be the response from a 4^ BO test of a patient with a Left Microtropia if the prism is placed before the RE

A

Place prism before RE, therefore image displaced away from the fovea, and RE adducts to maintain fixation

Herrings Law: the LE moves. Now image falls within the suppression scotoma of the LE (i.e. brain is not aware that the target has moved), thus no diplopia results therefore NO nasal movement of the LE to maintain BSV
= microtropia with identity

i.e. NO disjugate movement to maintain fixation

50
Q

describe what will be the response from a 4^ BO test of a patient with a Left Microtropia if the prism is placed before the LE

A

Prism placed in front of LE, the image falls within the suppression scotoma, thus NO movement of either eye is seen
= microtropia with identity

51
Q

what is the management the same for

A

with and without identity

52
Q

what is the 5 aims/steps of management for microtropia

A
  • Optimise vision
  • Correct refractive error
  • Constant glasses wear
  • Glasses adaptation
  • Occlusion (patch/atropine)
53
Q

how long does the patient have to adapt to their glasses i.e. how long can it take and what needs to be done it adaptation does not occur

A
  • up to 16 weeks for maximum for optimal vision with specs

- if no adaptation, then move onto patching/occlusion

54
Q

when will you decide to occlude a px with amblyopia and why
how long is occlusion continues for
what is the optimum post treatment VA
what can be done if a px has good motor fusion
what is the risk of occlusion for a patient who is over the age of 7

A

If VA is still down, done to treat px for amblyopia

Occlusion continued until no further improvement over 2 or 3 visits (a couple of months apart)

Optimum post treatment VA often 6/9 or 6/12 or one line below other eye

If good motor fusion, can occlude after 7/8 year cut-off (compared to if px has poor motor fusion)

If poor / absent motor fusion and over 7 years old =
risk of INTRACTABLE DIPLOPIA if occluding as can eliminate suppression scotoma

55
Q

list the 5 HES criteria for discharge a micro tropic px has have
what is this also a good level for

A
  • Stable visual acuity
  • Up to date refraction
  • Gls / CL for long term
  • Static angle of deviation
  • Asymptomatic

this is also a good level to retry occluding if previously poor compliance

56
Q

list what three things in a patient will make you want to investigate for microtropia

A
  • Reduced uniocular vision
  • Anisometropia
  • Abnormal binocular vision

Binocular vision YR 3 (20 decks)

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