lecture 2 - strabismus, latent and manifest Flashcards
heterotropia is… strabismus
manifest or squint
Heterophoria is …. strabismus
heterophoria
tropia
both fovea aren’t looking at the same object
can you always see a strabismus
no - need to do cover test
what causes psuedostrabismus
epicentral folds wide inter pupillary distance unilateral myopia or exophthalmos facial asymmetry large angle kappa
what is angle kappa (K)
the angle between the centre of pupil and corneal reflection
in normal people what is angle kappa (K)
3 - temporally to posterior pole
in central corneal reflexes what is angle kappa
0
if the fovea lies nasal to the posterior pole what is angle kappa
negative - as corneal reflection is temporal
how to detect pseudo strabismus
use corneal reflection and see if they are symmetrical
use cover test
what is cover test used for?
pseduostrabismus
latent (phobia)
manifest (tropia) deviation
what is cover/uncover test used for?
used as a test to detect manifest
what is alternating cover test for?
best test to detect Heterophoria as it fully dissociates
if you find esotropia at near …
also use a light
why do you always use corneal reflections initially?
easier to do with young children and adults with learning difficulties and can determine if someone has eccentric fixation
when you are not using your fovea for central fixation
eccentric fixation
what is the accommodative target for cover test
line above worst VA or toys for infants
cover test is only as good as…
patients fixation
what is the largest reason for misdiagnosis
poor fixation
how do you control a px’s fixation
ask them questions about it - eg, when looking at bird, ask what colour the beak is, how many legs is he standing on etc
when do you look at the eye on cover/uncover
as you are covering one eye you observe the movement of the other
COVER/UNCOVER:
if eye moves out
esotropia
COVER/UNCOVER:
if eye moves in
exotropia
COVER/UNCOVER:
if eye moves up
hypotropia
COVER/UNCOVER:
if the eye moves down
hypertropia
Hering’s law
when a muscle in one eye contracts a muscle in the opposite eye also contracts in order for both eyes to work together
what does constant tropia mean
both eyes uncovered the patient will always go back to fix with one eye
what do you record when recording results for tropia
- which eye is affected
- what distance it was measured at
- degree of movement
- target used
minimal deviation is
<10 prism dioptres
small deviation is
10-20 prism dioptres
moderate deviation
20-40 prism dioptres
large deviation
> 40 prism dioptres
Heterophoria
when the eyes are dissociated the eyes deviate from the fixation point
orthophoria
no phoria or tropia
when do you look at the eye on alternating CT
watch the eye as you remove the cover
movement on alternating: esophoria
eye moves out
movement on alternating: exophoria
eye moves in
recording results for phoria
- direction of deviation
- degree of deviation
- speed of recovery
- distance
- target
- whether specs were worn
how to analyse cover test?
- is it cover/uncover or alternating
- what does the uncovered eye do to take up fixation
- if it moves out then it was Esophoria
- if it moves in it was eco
- if nothing found and it moved out on alternating then it was SOP
