manifest and latent strabismus Flashcards
what is manifest strabismus known as ?
heterotropia
what is latent strabismus known as ?
heterophoria
what is no tropia?
.both foveas simultaneously looking at the object
what is manifest strabismus/tropia?
. both foveas are not simultaneously looking at the object
what are the different types of manifest strabismus?
. left esotropia (LSOT)
. left exotropia ( LXOT )
. left hypertropia ( left eye is higher )
. right hypertropia
. L incyclotropia- eye is turned in an anti-clock wise towards the nose
. L excyclotropia - eye is turned in a clock-wise fashion
why can’t you always diagnose a strabismus by looking at the appearance of the eye?
. not all tropias large enough to be cosmetically noticeable
. smaller angle tropias can appear normal
what to test to use to determine if a px has a tropia?
. cover test required to determine if they have tropia or not
what is a pseudostrabismus ?
. gives the appearance of a tropia when normal
. cover test required to determine if they have tropia or not
-can see from the corneal reflex in the eyes.
why can a pseudostrabismus occur in young infants ?
. this is due to the skin around the nose , extra skin around the nose happens in young infants because their nose hasn’t fully formed yet
. therefore infants end up with a lot of skin around their nose , this gives a rise to the appearance of a squint
what are the reasons for the appearance of a pseudostrabismus ?
. epicanthal folds ( skin around nose - most common types
. different lids position
. wide interpupillary distance
. unilateral myopia or exopthalmos
. facial asymmetry
. variation of angle kappa
what is angle kappa?
. angle between optical axis and visual - not coincident
why does angle kappa give rise to pseudostrabismus?
. instead of corneal reflections being right in the centre of the pupil, because most people’s fovea is temporal to the posterior pole
. the corneal reflection will be slightly off centre from the pupil, thus giving rise to pseudostrabismus
what is the the angle of kappa in a normal eye?
. normal position of corneal reflexes positive kappa angle of 3deg, this is because the fovea lies temporally to the posterior pole
-so corneal reflections will be nasal
. exotropia is observed
what happens when the fovea is coincident with the posterior pole?
. angle kappa is zero
. eye look completely central
what happens when fovea lies nasally to posterior pole?
. rarely fovea lies nasally to posterior pole and corneal reflex is temporal. resulting in a negative angle kappa
. esotropia is observed
how to detect pseudostrabismus?
. corneal reflections - hold pen - torch 30cm for patient’s eye and look to see if they are symmetrical
when to use corneal reflections when detecting pseudostrabismus?
. useful in uncooperative children and adults
. can only be used in moderate large deviations
. small deviation need cover test
what does it mean if corneal reflection is temporal ?
eye is esotropic
what does it mean if corneal reflection is nasal?
eye is exotropic
what is a cover test used to decide?
used to decide:
. pseudostrabismus
. latent (phoria)
. manifest ( tropia ) deviation
what can a cover test be broken into?
- cover/uncover test
- used as a test to detect manifest strabismus ( tropias) - alternating cover test
- best test to detect heterophorias as it fully dissociates ( makes the deviation as large as possible )
how is a cover uncover test carried out?
. carried out:
- 1/3 m - near
- 6m
- > 6m if deviation increases distance
. need to carry out the cover test with an accommodative target ( with tiny letters)
- line above worst V-A
- the beak of the bird
. need to carry out the cover test with light
. with and without spectacle prescription
- this is because spectacle prescription will influence size of deviation
. with and without head posture
why do we carry cover test with and without spectacle prescription?
- this is because spectacle prescription will influence size of deviation
- convex lenses relax accommodation and therefore will relax convergence
- convex lenses makes an eco deviation better and exo deviation worse - important to do with and without posture
what are some cover test tips?
- always light and always use corneal reflections
- always use accommodative target
- infant use small toys
- older child ( knows letter ) line above worst VA - your cover test is only as good as your patients fixation
why might someone not move eye during cover test but still have manifest deviation ?
. this might be due to a visual impairment
. young children and adults with learning difficulty may not move eye because they don’t understand what you’re asking them to do
. they have eccentric fixation- not using fovea
what does it mean by always using an accommodative target?
. check what either eye can see and then you always choose the line above the worst VA
. if their worst VA was the 6/9 line , then you would use 6/12
why is your cover test only as good as your patients fixation ?
. poor fixation is the biggest reason for misdiagnosis
how do you control a patients fixation ?
. ask the px questions about the target
. if you get correct response you know px fixation is good
what is the main reason for cover/uncover test?
to look for manifest deviation
explain the cover/uncover test?
- ensure head straight and still
- cover the right eye and observe left eye
- if left eye is deviated, it will move to take up fixation
if it moves:
- out, it was convergent= left esotropia
- in, it was divergent = left exotropia
- down, it was elevated= left hypertropia
- up, it was depressed = left hypotropia - repeat by covering left eye and observing right eye
. you look at the right eye as you’re covering the left
. always look at how the uncovered eye is moving to take up fixation
what is 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 happens when right eye is straight( fixing on the target) is covered and left eye esotropic (L SOT) ?
. when the right eye is covered, the left uncovered and eye moves out ( to left ) to take up fixation
. hering’s law means that the right eye will also move to the left
. when the cover is removed the left eye moves back in to the right
. the right eye also moves back in ( to the right ) to become straight again
what happens when you cover the left esotropic eye and the right straight eye is uncovered?
. when you cover the left eye
. right eye straight ( fixing ) no movement
what happens when right eye is straight and covered and left eye is elevated L HYPERTROPIA?
. right eye is covered
. left uncovered eye moves down to take up fixation
. right eye also moves down behind the occulder ( becomes right hypo phoria ) because of hering’s law
. when the right eye is uncovered
. left eye move up ( returns to L hypertropia )
. right eye also moves up ( now straight )
what happens when straight right eye is uncovered and left eye is elevated and covered ?
right eye will not move
what happens when we have right straight eye covered and left esotropia ? the px also has alternating esotropia
- right eye covered so the left uncovered eye moves out ( to the left ) to take up fixation ( its now straight )
- right eye behind the occluder also moves to the left due to hering’s law ( R eso deviation )
- when the occluder is removed the right eye stays in toward the nose due to alternating esotropia
- alternated from being a left esotropia to right esotropia
- when left is eye covered , right uncovered eye must move out to the right to take up fixation
- the patient may show a preference to fix with one eye
- record as Alt SOT if no preference or L SOT if there is a preference
how to record results?
. need to say it was cover test you are carrying out
. which eye ?
- right, left or alternating
. did px wear glasses?
.what distance was it measured ?
- distance (D), near ( N) , far distance ( FD)
- degree of movement
. minimal, small, moderate or large
. is there double vision?
- target used
. accommodative or no accommodative ( light )
how to record deviation?
. minimal
. small
. moderate
. large
what is heterophoria/ latent strabismus ?
. when both eye uncovered, the visual axis are directed towards the fixation target
. when an occluder is put in place, the eye behind the occluder deviates away from the fixation point
what is orthophoria ?
. with both eye uncovered, the visual axis are directed towards the fixation target
. when the eyes are dissociated ( i.e covered by an occluder ) the visual axis are still directed towards the fixation target
what are the types of heterophoria ?
. SOP ( nesophoris )- turns in towards the nose
. XOP ( exophoria ) - turns out towards the temple
. L hyperP- turns upwards
.R hyper P
.incycloP - twisted in anti-clock
.ExcycloP- twisted clock wise
what test to use for heterophoria ( latent strabismus)?
. you must always carry out a cover uncover test initially to confirm no manifest deviation before moving onto alternating cover test
. if on cover uncover test , you find a manifest deviation then it is not a heterophoria
what is the best method for heterophoria ( latent strabismus)?
. alternating cover test is the best method to detect heterophoria as it fully dissociates ( makes the deviation bigger)
how to carry out alternating cover test?
. patient sits with their head erect
. patient fixates a suitable target
. alternate the occluder between the two eyes
. the patient must never be able to see the target with both eyes
. continue alternating the occluder until the deviation no longer increases in size
. move the cover at an appropriate speed
- the slower the better
how to look at the eye during heterophoria- alternating cover test?
. the movement of the uncovered eye is noted as you move the occluder between eyes
. at the end of the alternating cover test watch as you remove the occluder
. when you remove the occluder from both eyes , you must note the recovery - how quickly the eye takes to move back up to a straight position
what does it mean if the eye does not move back to take up fixation?
it is manifest strabismus
what happens when both eye have no manifest deviation and you cover them and carry out alternating cover test ?
esophoria in RE
. when we cover right eye and it’s an esophoria
. the eye behind occluder will turn in towards the nose
. alternating cover test- occluder moved from RE to the LE
. the uncovered eye moves outwards to the right to take up fixation
. as the eye moves outwards to take up fixation then it was inwards to begin with ( esophoric )
. the eye behind the occluder moves in towards nose to take up fixation
what happens when both eyes have no manifest deviation and an alternating cover test is carried out ?
exophoria
. when an occluder is placed in front of RE fusion is suspended and the eye behind the occluder moves out
. when the cover is moved from RE to the left. uncovered right eye moves inwards to take up fixation
. as the eye needs to move inwards to take up fixation then it was outwards to begin with ( exophoric )
. the LE now behind the occluder ( fusion suspended ) then LE moves out
what happens when no manifest deviation and an alternating cover test is carried out?
right hyperphoria
. occluder placed in front of RE, RE elevates
. cover moved from RE to the left eye, the right uncovered eye moves downwards to take up fixation
. as the eye needs to moves downwards to take up fixation it was elevated to begin with ( right hyperphoria )
. LE now occluded- as RE moved down to fixate due to hering’s law the left eye also moved down ( it is a left hypophoria )
. if you were to move occluder from LE to RE then LE would move up ( left hypophoria )
how to record results in latent deviation?
- record direction of deviation
- esophoria not right or left esophoria
- exophoria not right or left exophoria
- right hyperphoria
- left hyperphoria
- record degree of deviation
- minimal, small, moderate or large - speed of recovery
- rapid recovery(r.r), noderate recovery(m.r.) or slow recovery(s.r.) or to blink
- the speed of recovery is important as the faster the speed of recovery, the better the control of the deviation
- distance
- distance, intermediate or near - target
accommodative or non-accommodative - whether spectacle worn
When do you look at each eye to check for manifest deviation ?
- check when cover one eye then look at the other eye
if no movement- then no trophia . - only look when one eye is covered
