Microtropia Flashcards
What is a microtropia?
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
What’s a primary microtropia?
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)
What’s a secondary microtropia?
Residual microtropia following treatment for larger manifest deviation
What are the types of microtropia?
- Microtropia with Identity
- Microtropia without Identity
What is Microtropia with Identity?
- 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
What is Microtropia without Identity?
- 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
How do we investigate microtropia?
- 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
What will visual acuity look like in a microtropia?
Poorer visual acuity in microtropia eye and so amblyopic & thus struggle with crowded VA tests
What will a cover test look like in a microtropia?
With Identity = no manifest
Without Identity = very small manifest
What will BSV tests look like in a microtropia?
- 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
What will a suppression scotoma look like in a microtropia?
- 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
How do we look at how someone is fixating in a microtropia?
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
What will a prism cover test show in a microtropia?
Simultaneous = manifest
Alternate = manifest & latent
How do we manage a microtropia?
- 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
What else might a microtropia be called?
Microstrabismus/Flick ET
What’s monofixation syndrome (Parks 1971)?
Use to describe microtropia but also others like subnormal BSV and unilateral macular pathology often in American literature
Can you have an ET with ARC that’s not a microtropia? How would this be shown?
Yes. Shown by >10PD, poorer BSV and fixation with anatomical fovea monocularly but pseudo-fovea when BEO
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