Strabismus - latent & manifest Flashcards
how are the position of our eyes when we look straight ahead
slightly divergent due to position of eyes in the bony socket but for some can be slightly convergent
what position do our eyes adopt when they are slightly divergent due to the bony socket
fusion free position
what are the eyes less divergent than when in the fusion free position
anatomical rest
what do we get when we uncover our eyes e.g. open when wake up
fusion
what is fusion
visual axis is parallel
what sort of BSV does fusion give
good
what is manifest strabismus
a condition in which the foveas of both eyes are not simultaneously aligned on the object of regard (on one eye it falls on foveal point but on other eye falls on a extra foveal point) = visual axis not parallel for distance vision
which two types of manifest strabismus are there
- constant
or - intermittent (e.g. when very tired or doing close work)
what can the deviations of manifest strabismus be
- horizontal
- vertical
- torsional (eye turns on sagittal axis)
- combination of all
name some synonyms of manifest strabismus
heterotropia
tropia
manifest deviation
manifest squint
name some patient terminology of manifest strabismus
lazy eye
wall eye
cast in eye
squint
give an example of a manifest strabismus when the visual axis may converge
a right esotropia/convergent strabismus
px is looking with left eye but right eye turns in
give an example of a manifest strabismus when the visual axis may diverge
a right exotropia
px is looking with left eye but right eye is turning out
give an example of a manifest strabismus when the visual axis may be elevated
a left hypertropia
px is looking with right eye but left eye is deviated upwards
give an example of a manifest strabismus when the visual axis may be depressed
a left hypotropia
px is looking with right eye but left eye is depressed downwards
define cyclo or torsional deviations
a misalignment of one or both eyes around the saggital axis
what is a clockwise deviation termed in torsional deviations
incyclorotation
what can cycle/torsional deviations be associated with
vertical deviations
what is an anti clockwise torsional deviation termed
excyclorotation
what is the name of a right eye turning clockwise
right incyclotropia
what is the name of a left eye turning anti clockwise
left excyclotropia
why is torsional deviations subjective
cannot see by observation so can see the eye going up or down but not rotating (can if have an iris freckle e.g. can see it move from 6-7 o’clock)
so have to rely or px’s description where one image will be tilted & one straight so will get double vision
when can manifest deviations not look cosmetically noticeable
in a smaller angle, the visual axis looks parallel
when a manifest deviation does not look cosmetically noticeable, what tests are required to determine a presence or absence
cover & uncover test
what is a pseudostrabismus
patient appears to have a strabismus but visual axis are actually aligned
give examples of reasons for pseudostrabismus
- wide epicanthal folds e.g. extra skin as no bridge formed on babies nose so covers some inner sclera
- wide PDs can look like exodeviation & narrow PDs can look like esodeviation
- unilateral myopia or exopthalmos
- facial asymmetry eg ptosis or proptosis
what is proptosis
from thyroid eye disease due to lots of inflammation in the orbit & the inflammatory process elevates the upper eyelid & gives a staring appearance which also pushes the eye out due to the inflammation infiltrating the fat in the orbit
how else can we check for deviations of the eye
compare the position of corneal reflexes between the two eyes
what is angle kappa
angle between the centre of the pupil and the corneal reflection (the visual axis to the optical axis)
what is the result of the angle kappa and corneal reflection if the fovea corresponds with the posterior pole of the eye
angle kappa = 0
corneal reflection = central
explain the normal positioning (looks slightly nasal) of corneal reflexes
positive kappa angle of 3 degrees
fovea lies temporally to posterior pole
explain the central positioning of corneal reflexes
angle kappa is 0
fovea coincides with posterior pole
explain the temporal positioning of corneal reflexes
negative angle kappa
fovea lies nasally to posterior pole
which is the most rare positioning of corneal reflexes
temporal
how do you test for pseudostrabismus
hold a pen torch 30cm infront of px eyes and examine their corneal reflections
what do the corneal reflections have to look like for a px to have pseudostrabismus
symmetrical
what type of patients are corneal reflexes good for
uncooperative children eg when cover test is not possible
at what distance should a cover uncover test be carried out for distance
6 meters viewing for distance
&
preferred working distance for near
(no need to be carried out for intermediate as if there is no deviations/symptoms at dist or near, there wont be for intermediate)
when will a testing distance for the cover uncover test be required at more than 6 meters
px with exo deviations
give an example of an accommodative target for the cover uncover test
snellen/logmar letter
give an example of a non accommodative target for the cover uncover test
pen torch for near
&
spotlight for distance
when are non accommodative targets used
when a px has eso deviations at near or distance
which letter on the snellen chart is most suitable to test with
a letter on the line above that which the weakest eye can read
eg. R v/a = 6/9 & L v/a = 6/6 use 6/12
which letter on the budgy stick is most suitable to test for near
one which is on the line above what the px could see with their weaker eye
if a px can see with both eyes which target should be used for testing at distance
a letter on the snellen/logmar chart
not a spotlight
what is the hering’s law of equal innervation
when one eye moves, the other eye will follow
eg. during cover test if one eye moves in, the other eye will move out then back in (takes up fixation) the middle so it will briefly follow the same direction
what is the exceptions to hering’s law
pathological conditions
what triggers hering’s law
when impulses are sent to extraocular muscles to move the eyes
so the corresponding muscles in each eye receive equal innervation to either contract or relax
what eye movements does hering’s law apply to
all eye movements including vergences
eye movement of one eye is not always observable
give an example of herring’s law with a left esotropia/left convergent strabismus
- record left esotropia as LCS or L ESOT
- cover px right eye
- left eye will go out to take up fixation
- right eye uncovered
- left eye will move right with the right eye
how do the both eyes react with a left esotropia/left convergent strabismus when the left eye is covered
as the left eye is deviated and right eye is fixated
when you cover the left eye, the right eye doesn’t move and the left eye also doesn’t move
explain what happens to a left exotropia/left divergent strabismus at near
- cover right eye
- left eye comes in to take up fixation
- take cover away
- right eye takes up fixation
- take cover away
- both eyes made vergent
- px fixes with right eye again
explain what happens to a left hypertropia
- fixing with right eye as the left eye is elevated
- cover the fixing eye
- left eye moves down
- & right eye also moves down under the cover
- take cover away
- both eyes move up
- then right eye takes up fixation again
- record as L HYPERT
what is an alternating esotropia
there is no preference over which eye fixates and which eye deviates
explain what happens to an alternating esotropia starting with fixing with the right eye
- px fixing with right eye
- right eye covered
- left eye diverges to take up fixation
- cover left eye
- remove cover from left eye
- px now fixes with left eye
how do you record an alternating esotropia with no preference
Alt ESOT
how of you record an alternating esotropia if there is a preference
eg. L Alt ESOT / R Alt ESOT
when a px with an alternating esotropia blinks, does the position of their preferred eye change
no
list the points to be mentioned when testing for a strabismus
- which eye
- what distance was is measured
- degree of movement
- target used
- with or without correction
how would you record which eye has the strabismus
right, left or alternating
how do you record what distance was measured
- distance D
- intermediate I
- near N
how do you record the degree of movement
- minimal
- small
- moderate
- large
how do you record the target used
- accommodative
or - non-accommodative
what is an example of recording results for a px with a strabismus
- D small R ESOT to act c rx
- N large EXOT to light s’ rx
what is a minimal deviation in prism dioptres
< 10
what is a small deviation in prism dioptres
10 - 20
what is a moderate deviation in prism dioptres
20 - 40
what is a large deviation in prism dioptres
> 40
give an example of how a 2 prism dioptre movement can be produced on a letter chart
when eyes from one end of the 6/9 line to the other
so ask px to look from beginning to end of the 6/9 line
what is a latent strabismus/heterophoria
if sensory function is artificially suspended
deviation of the visual axis will occur in most individuals (under the occluder only, so when move occluder away, the eyes align for distance visual axis i.e. motor fusion is allowed to return)
when can a latent strabismus/heterophoria also occur
when present different images to both eyes
if you don’t have a manifest deviation what sort of deviation will you have
latent
name some other words for latent strabismus
- heterophoria
- phoria
- latent deviation
- latent squint
whats happens to the visual axis in latent strabismus
- converge - esophoria
- diverge - exophoria
- elevate - hyperphoria
- depress - hypophoria (redundant term is right hyperphoria is same as left hypophoria as it is a binocular deviation but always state the hyper eye)
explain the heterophoria alternating cover test
- px sits with their head erect facing a letter chart
- px is directed to fixate on a suitable target (letter from line above that weaker eye can see)
- if no manifest deviation is present:
alternate the cover between the two eyes
continue until the deviation no longer increases in size
remove the cover and observe the movement of the right eye
repeat the procedure and this time remove the cover from the left eye
move the cover at an appropriate speed (each eye covered for about 4 seconds)
what happens to the visual axis in heterophoria if as you take the cover away
- the right eye moves out - esophoria
- the right eye moves in - exophoria
- the right eye moves down - right hyperphoria
- the right eye moves up - left hypophoria (other eye moves down)
- occasionally both eyes go up behind the cover
are heterophorias a binocular or monocular condition
binocular
very rarely monocular, only in anisometropia
explain what happens during a near exophoria
fixated/uncovered eye moves in during cover test
how do you record the results of latent deviations
- direction of deviation
- degree of deviation
- speed of recovery
- distance
- target
how would you record the degree of deviation in latent deviations
- minimal
- small
- moderate
- large
or - othophoria
how would you record the speed of recovery in latent deviations
- rapid recovery (r.r.)
- moderate recovery (m.r.)
- slow recovery (s.r.)
- blink
give an example of recording results for a px with latent deviations
D. mod esop r.r. to light, N. large exop s.r.
what is an example of a better recovery
fast recovery = better control over their bsv and worse with slow recovery
when accommodation is exerted, what is it coupled with
convergence
give an example of accommodation exerted with convergence
1 dioptre of accommodation is usually associated with 4 prism dioptres of convergence so eg. if we accommodate by 4D we converge by 16 prism dioptres
what will excessive accommodation (uncorrected hypermetropia) lead to
excessive convergence
if a px’s motor fusion is adequate (good bsv) what sort of deviation will they have
esophoria
a latent deviation and not manifest
if a px’s motor fusion is inadequate or if fusion mechanism is impaired what sort of deviation will they have
esotropia
a manifest deviation
what may alleviate the deviation
correcting the refractive error
in what type of px’s will by corrective the refractive error, alleviate the deviation
- fully accommodative esotropias
- esotropia with accommodative element
- non-accommodative esotropias
what is esotropia with an accommodative element
when a corrected child shows improvement with specs but still have bit of manifest deviation e.g. the deviation increases with the esotropic accommodation but when you suspend accommodation, its still present
what is non-accommodative esotropias
manifest esotropia, when you refract you only find e.g. +0.50D which won’t help
what can be an example of something becoming a manifest deviation e.g. an exodeviation
if you hold something at 33cm and don’t accommodate, you don’t converge, so the visual axis are more divergent and becomes an exophoria, and if fusion isn’t adequate enough to control the exophoria
what can eso deviations arise with
myopia
what can exo deviations arise with
hyperopia
