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Binocular vision > Strabismus - latent & manifest > Flashcards

Strabismus - latent & manifest Flashcards

1
Q

how are the position of our eyes when we look straight ahead

A

slightly divergent due to position of eyes in the bony socket but for some can be slightly convergent

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2
Q

what position do our eyes adopt when they are slightly divergent due to the bony socket

A

fusion free position

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3
Q

what are the eyes less divergent than when in the fusion free position

A

anatomical rest

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4
Q

what do we get when we uncover our eyes e.g. open when wake up

A

fusion

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5
Q

what is fusion

A

visual axis is parallel

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6
Q

what sort of BSV does fusion give

A

good

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7
Q

what is manifest strabismus

A

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

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8
Q

which two types of manifest strabismus are there

A
  • constant
    or
  • intermittent (e.g. when very tired or doing close work)
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9
Q

what can the deviations of manifest strabismus be

A
  • horizontal
  • vertical
  • torsional (eye turns on sagittal axis)
  • combination of all
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10
Q

name some synonyms of manifest strabismus

A

heterotropia
tropia
manifest deviation
manifest squint

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11
Q

name some patient terminology of manifest strabismus

A

lazy eye
wall eye
cast in eye
squint

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12
Q

give an example of a manifest strabismus when the visual axis may converge

A

a right esotropia/convergent strabismus

px is looking with left eye but right eye turns in

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13
Q

give an example of a manifest strabismus when the visual axis may diverge

A

a right exotropia

px is looking with left eye but right eye is turning out

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14
Q

give an example of a manifest strabismus when the visual axis may be elevated

A

a left hypertropia

px is looking with right eye but left eye is deviated upwards

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15
Q

give an example of a manifest strabismus when the visual axis may be depressed

A

a left hypotropia

px is looking with right eye but left eye is depressed downwards

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16
Q

define cyclo or torsional deviations

A

a misalignment of one or both eyes around the saggital axis

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17
Q

what is a clockwise deviation termed in torsional deviations

A

incyclorotation

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18
Q

what can cycle/torsional deviations be associated with

A

vertical deviations

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19
Q

what is an anti clockwise torsional deviation termed

A

excyclorotation

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20
Q

what is the name of a right eye turning clockwise

A

right incyclotropia

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21
Q

what is the name of a left eye turning anti clockwise

A

left excyclotropia

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22
Q

why is torsional deviations subjective

A

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

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23
Q

when can manifest deviations not look cosmetically noticeable

A

in a smaller angle, the visual axis looks parallel

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24
Q

when a manifest deviation does not look cosmetically noticeable, what tests are required to determine a presence or absence

A

cover & uncover test

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25
Q

what is a pseudostrabismus

A

patient appears to have a strabismus but visual axis are actually aligned

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26
Q

give examples of reasons for pseudostrabismus

A
  • 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
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27
Q

what is proptosis

A

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

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28
Q

how else can we check for deviations of the eye

A

compare the position of corneal reflexes between the two eyes

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29
Q

what is angle kappa

A

angle between the centre of the pupil and the corneal reflection (the visual axis to the optical axis)

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30
Q

what is the result of the angle kappa and corneal reflection if the fovea corresponds with the posterior pole of the eye

A

angle kappa = 0

corneal reflection = central

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31
Q

explain the normal positioning (looks slightly nasal) of corneal reflexes

A

positive kappa angle of 3 degrees

fovea lies temporally to posterior pole

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32
Q

explain the central positioning of corneal reflexes

A

angle kappa is 0

fovea coincides with posterior pole

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33
Q

explain the temporal positioning of corneal reflexes

A

negative angle kappa

fovea lies nasally to posterior pole

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34
Q

which is the most rare positioning of corneal reflexes

A

temporal

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35
Q

how do you test for pseudostrabismus

A

hold a pen torch 30cm infront of px eyes and examine their corneal reflections

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36
Q

what do the corneal reflections have to look like for a px to have pseudostrabismus

A

symmetrical

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37
Q

what type of patients are corneal reflexes good for

A

uncooperative children eg when cover test is not possible

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38
Q

at what distance should a cover uncover test be carried out for distance

A

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)

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39
Q

when will a testing distance for the cover uncover test be required at more than 6 meters

A

px with exo deviations

40
Q

give an example of an accommodative target for the cover uncover test

A

snellen/logmar letter

41
Q

give an example of a non accommodative target for the cover uncover test

A

pen torch for near
&
spotlight for distance

42
Q

when are non accommodative targets used

A

when a px has eso deviations at near or distance

43
Q

which letter on the snellen chart is most suitable to test with

A

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

44
Q

which letter on the budgy stick is most suitable to test for near

A

one which is on the line above what the px could see with their weaker eye

45
Q

if a px can see with both eyes which target should be used for testing at distance

A

a letter on the snellen/logmar chart

not a spotlight

46
Q

what is the hering’s law of equal innervation

A

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

47
Q

what is the exceptions to hering’s law

A

pathological conditions

48
Q

what triggers hering’s law

A

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

49
Q

what eye movements does hering’s law apply to

A

all eye movements including vergences

eye movement of one eye is not always observable

50
Q

give an example of herring’s law with a left esotropia/left convergent strabismus

A
  • 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
51
Q

how do the both eyes react with a left esotropia/left convergent strabismus when the left eye is covered

A

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

52
Q

explain what happens to a left exotropia/left divergent strabismus at near

A
  • 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
53
Q

explain what happens to a left hypertropia

A
  • 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
54
Q

what is an alternating esotropia

A

there is no preference over which eye fixates and which eye deviates

55
Q

explain what happens to an alternating esotropia starting with fixing with the right eye

A
  • 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
56
Q

how do you record an alternating esotropia with no preference

A

Alt ESOT

57
Q

how of you record an alternating esotropia if there is a preference

A

eg. L Alt ESOT / R Alt ESOT

58
Q

when a px with an alternating esotropia blinks, does the position of their preferred eye change

A

no

59
Q

list the points to be mentioned when testing for a strabismus

A
  • which eye
  • what distance was is measured
  • degree of movement
  • target used
  • with or without correction
60
Q

how would you record which eye has the strabismus

A

right, left or alternating

61
Q

how do you record what distance was measured

A
  • distance D
  • intermediate I
  • near N
62
Q

how do you record the degree of movement

A
  • minimal
  • small
  • moderate
  • large
63
Q

how do you record the target used

A
  • accommodative
    or
  • non-accommodative
64
Q

what is an example of recording results for a px with a strabismus

A
  • D small R ESOT to act c rx

- N large EXOT to light s’ rx

65
Q

what is a minimal deviation in prism dioptres

A

< 10

66
Q

what is a small deviation in prism dioptres

A

10 - 20

67
Q

what is a moderate deviation in prism dioptres

A

20 - 40

68
Q

what is a large deviation in prism dioptres

A

> 40

69
Q

give an example of how a 2 prism dioptre movement can be produced on a letter chart

A

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

70
Q

what is a latent strabismus/heterophoria

A

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)

71
Q

when can a latent strabismus/heterophoria also occur

A

when present different images to both eyes

72
Q

if you don’t have a manifest deviation what sort of deviation will you have

A

latent

73
Q

name some other words for latent strabismus

A
  • heterophoria
  • phoria
  • latent deviation
  • latent squint
74
Q

whats happens to the visual axis in latent strabismus

A
  • 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)
75
Q

explain the heterophoria alternating cover test

A
  • 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)
76
Q

what happens to the visual axis in heterophoria if as you take the cover away

A
  • 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
77
Q

are heterophorias a binocular or monocular condition

A

binocular

very rarely monocular, only in anisometropia

78
Q

explain what happens during a near exophoria

A

fixated/uncovered eye moves in during cover test

79
Q

how do you record the results of latent deviations

A
  • direction of deviation
  • degree of deviation
  • speed of recovery
  • distance
  • target
80
Q

how would you record the degree of deviation in latent deviations

A
  • minimal
  • small
  • moderate
  • large
    or
  • othophoria
81
Q

how would you record the speed of recovery in latent deviations

A
  • rapid recovery (r.r.)
  • moderate recovery (m.r.)
  • slow recovery (s.r.)
  • blink
82
Q

give an example of recording results for a px with latent deviations

A

D. mod esop r.r. to light, N. large exop s.r.

83
Q

what is an example of a better recovery

A

fast recovery = better control over their bsv and worse with slow recovery

84
Q

when accommodation is exerted, what is it coupled with

A

convergence

85
Q

give an example of accommodation exerted with convergence

A

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

86
Q

what will excessive accommodation (uncorrected hypermetropia) lead to

A

excessive convergence

87
Q

if a px’s motor fusion is adequate (good bsv) what sort of deviation will they have

A

esophoria

a latent deviation and not manifest

88
Q

if a px’s motor fusion is inadequate or if fusion mechanism is impaired what sort of deviation will they have

A

esotropia

a manifest deviation

89
Q

what may alleviate the deviation

A

correcting the refractive error

90
Q

in what type of px’s will by corrective the refractive error, alleviate the deviation

A
  • fully accommodative esotropias
  • esotropia with accommodative element
  • non-accommodative esotropias
91
Q

what is esotropia with an accommodative element

A

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

92
Q

what is non-accommodative esotropias

A

manifest esotropia, when you refract you only find e.g. +0.50D which won’t help

93
Q

what can be an example of something becoming a manifest deviation e.g. an exodeviation

A

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

94
Q

what can eso deviations arise with

A

myopia

95
Q

what can exo deviations arise with

A

hyperopia

Binocular vision (12 decks)

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