Microtropia Flashcards

1
Q

What is a microtropia?

A

A microstrabismus that is a small angle manifest strabismus (unilateral) without BSV but better than ARC

Less than or equal to 10PD often with an associated latent strabismus

Have a subnormal BSV with sensory and motor fusion and reduced stereopsis (it’s rarely absent)

Have a foveal suppression scotoma and thus parafoveal fixation(slightly off the fovea)

Have reduced visual acuity

Anisometropia (1PD Sphere +ve difference between the 2 eyes) with often an astigmatism

More commonly Eso than Exo (vertical rare)

Subnormal stereoacuity

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2
Q

What’s a primary microtropia?

A

The initial primary defect with no larger angle strabismus but can accompany concomitant strabismus (E.g. left fully accommodative ET controlling to MT with identity)

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3
Q

What’s a secondary microtropia?

A

Residual microtropia following treatment for larger manifest deviation

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4
Q

What are the types of microtropia?

A
  • Microtropia with Identity
  • Microtropia without Identity
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5
Q

What is Microtropia with Identity?

A
  • CT shows no manifest deviation
  • Eccentric fixation which is coincident with angle of deviation
  • Harmonious ARC and absolute eccentric fixation don’t use anatomical fovea when uniocular/monocular
  • Angle of anomaly is equal to angle of eccentricity (CONGRUOUS)

E.g. CT c/gls
Nr Small E with good recovery
Dist small E with good recovery

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6
Q

What is Microtropia without Identity?

A
  • CT shows very small manifest deviation
  • Central fixation or eccentric fixation (not coincident with angle of deviation so angle of deviation doesn’t equal angle of fixation)
  • Central fixation and ARC
    OR
    Non-absolute eccentric fixation and ARC
    OR
    Central fixation and NRC, central suppression and extended Panum’s in periphery

E.g. CT c/gls
Nr v sl R ET without diplopia
Dist v sl R ET without diplopia
On dissociation increase to small E with good recovery to v sl R ET

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7
Q

How do we investigate microtropia?

A
  • Case history
  • VA
  • CT
  • BSV
  • Foveal Suppression Scotoma (prism reflex test with 4PD to small detailed target)
  • PCT (measure deviation size, measure manifest with simultaneous PCT, PCT for latent or manifest)
  • Refraction
  • Fundus & Media
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8
Q

What will visual acuity look like in a microtropia?

A

Poorer visual acuity in microtropia eye and so amblyopic & thus struggle with crowded VA tests

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9
Q

What will a cover test look like in a microtropia?

A

With Identity = no manifest
Without Identity = very small manifest

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10
Q

What will BSV tests look like in a microtropia?

A
  • Sensory fusion but with foveal suppression
  • Motor fusion shows compensation of latent component and can use sensory fusion ‘control’ by holding Bagolini over PCT to see if suppression occurs at break point
  • Reduced Stereoacuity
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11
Q

What will a suppression scotoma look like in a microtropia?

A
  • Foveal suppression (central)
  • Objective measures include 4PD reflex test both BO and BI with a detailed fixation target
  • Subjective measures include Bagolini where they may say there is a gap between the lines and dot in the X but this is difficult to see so may not report, and the polarised 4-dot test
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12
Q

How do we look at how someone is fixating in a microtropia?

A

To assess which part of the eye they’re fixing with monocularly we can use fixation ophthalmoscope/visuoscope. Fixation may be stable/fixed or wandering/flicking

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13
Q

What will a prism cover test show in a microtropia?

A

Simultaneous = manifest
Alternate = manifest & latent

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14
Q

How do we manage a microtropia?

A
  • Visual Acuity -
    Correct refractive error, wear refractive correction and amblyopia treatment (fixation tests give us prognosis for VA improvement)
  • BSV -
    Follow treatment for each type of concomitant strabismus; consider microtropia influence where decompensation of microtropia could lead to manifest strabismus and poorer treatment outcomes of associated concomitant strabismus
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15
Q

What else might a microtropia be called?

A

Microstrabismus/Flick ET

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16
Q

What’s monofixation syndrome (Parks 1971)?

A

Use to describe microtropia but also others like subnormal BSV and unilateral macular pathology often in American literature

17
Q

Can you have an ET with ARC that’s not a microtropia? How would this be shown?

A

Yes. Shown by >10PD, poorer BSV and fixation with anatomical fovea monocularly but pseudo-fovea when BEO

18
Q

SEE PRINTED SLIDES DESPERATELY

A