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
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
