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AMBV > Week 1.10 Concomitant Strabismus > Flashcards

Week 1.10 Concomitant Strabismus Flashcards

1
Q

Why does every px needs an assessment of their BV

A
  • binocular coordination and cooperation contribute to visual function and comfort
  • helps explain current symptoms or past visual development
  • provides indication of px cranial health
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2
Q

What is the average refraction of a newborn

A

+2.00DS (+/-2D) refraction changes as they get older
VA~ 6/120
Stereopsis >600sec
Poor accommodation accuracy and vergence control

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3
Q

When does stereopsis develop

A

BV not inborn, stereopsis develops during first year after birth
Series of conditioned reflexes develop in the first 3 years of life (critical period) to produce binocular input to cortical cells

These reflex become established by about 5 to 6 years, or later for some aspects (plastic period) and hence become unconditioned reflexes

Will never get to normal BV if did not have normal BV at end of critical period

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4
Q

Sensory and motor fusion

A

Sensory – ability to simultaneously appreciate two similar images, one with each eye, and to interpret them as one

Motor – ability to maintain a single image by correctly aligning the two visual axes during eye movements

Sensory fusion + motor fusion = BSV
BSV= binocular single vision

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5
Q

What are the grades of binocular vision?

A
  1. Monocular vision
  2. Simultaneous macular perception
  3. (Sensory) fusion
  4. Stereopsis
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6
Q

What is simultaneous macular perception

A

When signals transmitted from the two eyes to the visual cortex are perceived at the same time I.e. the ability to see two dissimilar objects simultaneously

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7
Q

What is the definition of strabismus

A

A deviation of the visual axes that cannot be overcome (controlled) by motor fusion. Constant vs intermittent

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8
Q

What does concomitant mean

A

Angele of deviation is the same in all directions of gaze
Also knows as: manifest deviation, heterophic, squint

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9
Q

What are the two main symptoms for binocular single vision with a person who has a strabismus

A

Diplopia - two uncrossed images
and confusion - crossed images one top of each other

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10
Q

What happen if a px develops strabismus before 3 years

A
  • Sensory adaptations from normal development occurs to prevent symptoms
  • leads to abnormal unconditioned reflexes developing by age of 6yrs (often ARC)
  • usually no symptoms
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11
Q

What happens if strabismus is acquired from 6yrs onwards

A
  • normal BV has been established
  • now at the end of plastic period so..
  • symptoms very likely to occur
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12
Q

If strabismus acquired between 3/6yrs?

A
  • symptoms initially occur
  • but system is unstable and readily breaks down
  • adaptations will develop (still in plastic period)
  • and again symptoms are unlikely to be reported
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13
Q

How do you work out if diplopia is monocular or binocular?

A

Monocular is less of a concern however binocular often related to cranial nerves

How to work out?
- cover each eye - diplopia remains
- if cover RE, LE still dip then there is monocular dip
- then cover LE, RE also dip which means both eyes have monocular dip and there’s 4 images going on
- if diplopia optical (due to large uncorrected astigmatism or cataract) - pinhole in dip disappears
- if diplopia remains with pinhole then cause within visual cortex

  • cover each eye - binocular disappears then binocular diplopia, next test is CT, expect to see manifest dev
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14
Q

What are the binocular sensory adaptations?

A

Global suppression
Abnormal/ anomalous retinal correspondence (ARC)

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15
Q

Monocular sensory adaptations

A
  • eccentric fixation
  • amblyopia
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16
Q

What’s the main aim of sensory adaptations

A

To prevent diplopia and confusion

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17
Q

Which binocular sensory adaptations usually occur in larger strabismus compared to smaller strabismus

A
  • In smaller strabismus <25prismD: both suppression and ARC often occur
  • In larger strabismus >25 prism D: suppression dominates
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18
Q

If the BV anomaly is well adapted (deep) what do we do

A

Don’t really have to do much if no symptoms

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19
Q

What are three reasons to intervene/treat BV anomaly

A
  • causing problems
  • likely to deteriorate if left untreated
  • if anomaly is sign of ocular or systemic,mic pathology
    Most will be referring to orthoptists in these cases
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20
Q

What is global suppression

A

Is a binocular sensory adaptations usually that occurs when the px is using both eyes in the prescence of a strabismus to avoid confusion and diplopia

Is a cortical adaptive phenomena which prevents images in the strabismic eye from reaching a conscious level

An obstacle in trying to restore normal sensorimotor function

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21
Q

Retinal rivalry

A

When different images are presented to normally corresponding point, the strongest image or dominant eye predominates

E.g. F L —> E

In strab eye corresponding point constantly receive diff img

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22
Q

How is suppression an elimination of retinal rivalry

A

Suppression is an elimination of retinal rivalry over the area from fovea to point receiving image (nasal in convergent strabismus)
- I.e the dominant eye ‘takes over’ for this area of the VF
- This loss of form in the deviated eye prevents confusion
Suppression is an anomaly of BV although it can also occur without strabismus in amblyopia (lazy eye reduction in VA of one eye)

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23
Q

What is normal retinal convergence?

A

Fovea’s of two eyes are corresponding neural points in cortex - all other points also corresponding

Normals can tolerate up to 2 degrees of visual axis misalignment

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24
Q

What is abnormal retinal correspondence (ARC)?

A

A binocular sensory adaptations occurs when the two fovea’s do not correspond to the visual cortex and instead a non fovea’s point in the deviated eye is associated with the fovea of the fixating eye in the cortex. Allows person to receive single image despite eyes being misaligned

Basically like rewiring of the eyes

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25
What is harmonious ARC (HARC)
The angle of rewiring matches the angle of strabismus Most common type of ARC Perfect rewiring to give binocular fixation
26
What is unharmonius ARC (UARC)
Very rare The retired point does not match the angle of strabismus Can be considered strab on top of strab Imperfect rewiring —> would still have diplopia
27
Ideal conditions for development of ARC
1. Strabismus before 6 years old (especially before 30 months) 2. Delay in treatment 3. Small constant strabismus angle 4. Esotropia>exotropia 5. Unilateral>alternating
28
Deep adaptations are well established so
Should be avoiding symptoms week Also more difficult to treat/remove
29
Strabismic px will manifest a choice of three sensory adaptations…
Diplopia - no sensory adaptations Global suppression - switching off an eye ARC - rewiring
30
Methods of investigation to differentiate suppression from ARC
Bagolini lenses Modified mallet unit Worths four dot test
31
Bagolini strained lenses
Used to differentiate suppression from ARC Trail case lens with grooves. Creates streak of glare 90 degrees to those striations At any viewing distance Ask PX if they see streaks of light Lenses position is to create 2 streaks 45 and 135 If one streak = global suppression If two streaks = HARC If two lights and lines = NRC 2 lines + strab = ARC
32
How do we measure the depth of suppression
Use neutral density filter bar In the case when you see ONE streak in Bagolini Place ND filter bar in front of **fixating eye** - increase filter until second line is seen - I.e. strabismic eye switches back on Can be used to measure depth of supp or arc - depending on what eye put filter bar in front of. If LE suppressed out par in front of RE so LE can switch back on Read units of the bar
33
How can you test the depth of ARC
In the case where you see 2 streaks in bagolini Placer NDF filter in front of **strabismic eye** - increase filter until ARC adaptation breaks down - line may disappear I.e be suppressed - or may get diplopia - 2 lights
34
Modified mallet unit OXO
Maintains a stimulus to binocular fixation Distance unit at 1.5m viewing distance Large OXO on newer mallet units In line with x top and bottom = HARC Only 1 line at bottom = supp Two oxo side by side one with line under one with top = NRC + diplopia OXOOXO - line top and bottom of x = UARC Measure depth with filter bar slightly to bagolini
35
What’s the issue with the modified mallet unit?
Slight problem = reduced illumination due to Polaroid filters is greater dissociation than occurs with bagolini - may miss some ARC
36
What is the worth’s four dot test?
Px wears red and green goggles 1 red, 2 green and 1 white dots Only. Check for gross stereopsis and can produce many false positive/negative results Red filter on right eye Green filter on left Px sees 4 lights = normal fusion If px sees 2 red lights = left suppression If pc sees 3 green lights = right suppression If px sees 2 red lights and 3 green lights = diplopia Green and red lights alternating = alternating suppression
37
What are the potential problems with the worths four dot test
It disrupts normal binocular difference due to the different colours producing rivalry between 2 eyes Decrease in light level as well A suppression area may fall within the centre of the test and miss all the dots
38
What is the definition of eccentric fixation?
When a non foveal point is used for fixation under monocular viewing conditions Common feature of amblyopia Usually only occurs in testing room as px usual fixates with other eye
39
When do you test for eccentric fixation
Only look for it when you have reduced VA
40
If the angle of EF matches angle of deviation what do you see on the CT
No movement is detected on cover test
41
How do we investigate eccentric fixation
- project target on retina - visible by both px and prac - px is asked to loom at centre of target and position of fovea is noted - position is then recorded in diagram and also record - steady/unsteady, usually EF is slightly nasal in SOT - can calibrate using the size of the optic disc
42
In amblyopia what is the rough guide for how much reduced the VA is
In amblyopia – reduced VA by one snellen line per 0.5 degree of eccentricity (very rough guide)
43
What are the other ways of investigating EF
- past pointing - after-image - perimeter - blind spot, ambler grid - corneal reflex - entropic phenomenon
44
How do we investigate EF with past pointing
Related to egocentric localisation - good eye first - checks normal ability amid increases confidence - occlude amblyopia eye, hold pen 25cm from px and as px to touch pen with tip of their finger - repeat with normal eye occluded If finger goes few cms to side then past pointing demonstrated - do not repeat as px can adapt - result indicates fixation does not coincide with the centre of localisation
45
How we investigate EF with corneal reflex
- compare reflex position in each eye in turn with the other eye occluded - relative displacement of the reflex by 1mm= approx 11 degrees or 20PD - eccentricity is not usually this great however making EF difficult to detect by this method
46
How can we investigate eccentric fixation with perimetry?
Normal subjects blind spots = same angular distance from fixation in both eyes - depends on rx Should be 15 degrees +/-3degrees Plot blind spots carefully in both eyes and compare positions Degree of eccentricity can be measured by the difference in angular distance of blind spot in each eye Required exceptional px cooperation and steady fixation
47
How can we investigate eccentric fixation with amsler grid
Amblyopia may have a small foveal scotoma which shows up as disturbance on amulet Occurs centrally if central localisation Eccentricity if EF Not very convincing test
48
How do we investigate eccentric fixation using the after image test
After images are transferred to normally corresponding points in the eye E.g. photography flashgun is masked to provide a very bright strip of light Occlude amblyopia eye and px fixates the centre of the strip Flash then produces a central after image
49
How do we record EF
- centricity of fixation (central vs eccentric) - if eccentric record whether it is temp nasal inf or sup - magnitude - size - quality of fixation (steady/unsteady/wandering) - pattern of fixation (drifts,saccades, nystagmus) - percent foveation - Directional bias (nasal, temporal) - subjective localisation of primary visual direction
50
What is the treatment for eccentric fixation?
- in amblyopia have to encourage foveal fixation - patch - direct occlusion alone may improve fixation but often a slight eccentricity remains - after image transfer - use to locate foveal fixation - pleoptic treatment desensitises eccentrically fixing area Established EF hard to remove
51
What is a microtropia?
Manifest deviation Definition: a misalignment of the eyes with an angle of deviation so small (less than 10 prism dioptres) that is usually assumed to also be fully adapted - (to further improve binocularity)
52
What types of microtropia are there
Primary microtropia: - unknown aetiology - maybe genetic element Secondary micrtropia: - residual deviation after optical or surgical treatment of larger strab - more prevalent
53
When does microtropia usually occur
Happens early in life - don’t find till later as infant unreliable in tests Frequently present between 2-3yrs May find on routine check as VA is slightly low - may even appear as phoria on CT Made evident by crowding phenomenon Exo is rare usually eso
54
Microtropia with identity
Angle of EF = habitual angle of deviation - no movement when dominant eye is covered on CT - need very subtle tests to diagnose
55
Microtropia without identity
Angle of EF not equal to angle of deviation - small movement when dominant eye is covered on CT Made evident - may not actually have EF but usually inaccurate
56
What does microtropia feel like for px
Usually asymptomatic And often no movement seen on CT so how can we find out of something is wrong?
57
Visual acuity: microtropia
Presence of amblyopia in one eye is usually the first clue to microtropia - likely to still get 6/6 to 6/12
58
What is crowding phenomenon
Crowding phenomenon is present with amblyopia and microtropia Letters may be missed due to central (suppression) scotoma - they may be doing more well on the letters on the outside/edges over a few lines Usually also have ~1.50D of anisometropia - but can have equal rx in each eye
59
What is the 4 dioptre prism test
- 4 base out placed before dominant eye - img moves across retina and the eye moves to take up fixation - non dom eye moves latrerally in same direction as its not fixating - versional movement is seen - prism is then removed and a recovery versional movement is seen - prism then placed before amblyopia eye - image moved across retina within suppression are: no movement of either eye
60
What confirms the presence of microtropia
Amblyopia + no CT movement + positive 4prism dioptre test = microtropia
61
To be able to describe somebody as microtropia:
- small angle <10PD - amblyopia - eccentric fixation - HAC on bagolini or modified mallet unit
62
How do you manage a microtropia
- refractive error correction - esp in high anisometropia - aniseikonia may be a problem - contact lens correction may help - refer to treat underlying amblyopia by occlusion of non squinting eye (if px <6yrs old)
63
What treatment options are not appropriate for microtropia
Orthoptics not app Surgery not app In px >6yrs - correct refractive error otherwise do not treat the mt Most cases correction of refractive error if necessary is only profitable action
64
What treatment options are not appropriate for microtropia
Orthoptics not app Surgery not app In px >6yrs - correct refractive error otherwise do not treat the mt Most cases correction of refractive error if necessary is only profitable action

AMBV (18 decks)

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