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(1) Concomitant Strabismus and Visual Development > Week 2 - Amblyopia > Flashcards

Week 2 - Amblyopia Flashcards

1
Q

What is amblyopia?

A

• A reduction in vision in one or both eyes, persistent after correction of refractive error.
• Absence of retinal pathology or any disease of the afferent visual pathway.
• Most common cause of vision loss in children. Interruption of normal visual development.

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2
Q

Mechanisms of amblyopia

A
  1. Deprivation of Form Vision
    • Can be partial or complete
    • Complete: No image/stimulus reaches fovea
    • Partial: Degraded imaging reaching fovea
  2. Abnormal Binocular Interaction
    • Incomplete images fall on the retina
    • Images are incompatible
    • Eyes compete for control over cortical connections during development period-better eye gains control
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3
Q

What does amblyopia look like for the Px?

A

• Reduced Snellen and grating acuity
• Loss of contrast sensitivity
• Shape distortion
• Motion deficits
• Crowding effect

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4
Q

What four senses are needed for visual function?

A
  1. Light sense
  2. Form sense
  3. Colour sense
  4. Motion sense
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5
Q

Describe 1. light sense and 2. form sense

A
  1. Light sense
    • Most primitive
    • Ability to distinguish light and dark
    • Rods
  2. Form sense
    • Ability to distinguish between spatially
    separate visual stimuli
    • Ability to discern size and shape of objects
    • Position and orientation
    • Rods and cones
    • Most acute at fovea
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6
Q

Describe 1. Colour sense and 2. Motion sense

A
  1. Colour sense
    • Distinguish between light of different wavelengths
    • Cones
  2. Motion sense
    • Ability to detect movement of images across retina
    • Visual cortex
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7
Q

What are the periods of visual development?

A

• Critical Period: A few months old - approximately 5 years old. Deprivation causes damage

• Sensitive Period: Time of deprivation- teenager years*
Amblyopia less likely to occur but improvement possible
*Some evidence in adult cases too

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8
Q

Describe critical period

A

• Period with active neural plasticity (ability of the neural system to undergo change).
• Period where deprivation impacts visual development and amblyopia can develop.
• Amblyopia can only develop within this time.
• Earlier the onset of deficit + the longer the period of deprivation= worse the outcome.

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9
Q

Describe sensitive period

A

• Improvement is possible during this time.
• The younger the patient= the quicker the response to treatment.
• Less common after 8 years of age.

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10
Q

strabismus and the brain?

A

• Abnormally high proportion of monocular cells the visual cortex where there should be binocular cells.

•Abnormal visual cortex may be responsible for loss of binocular stereoscopic vision.

• Alternating strabismus results in equal number of cells for right and left and virtually no binocularly driven cells.

• Acuity responses in convergent eyes of monkeys reported to be reduced at the retinal ganglion cell (RGC) layer & lateral geniculate nucleus (LGN).

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11
Q

Classifications of Amblyopia:

A

• Functional
Improvement after treatment is expected
- Strabismic
- Anisometropic
- Stimulus Deprivation
- Meridional
- Ametropic

• No lesion
May be reversible or irreversible
- Organic:
- Toxic

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12
Q

Strabismic amblyopia:

A

Result of constant or near-constant childhood strabismus in one eye.
Mostly esotropias as many exotropia’s are intermittent in childhood.

Clinical Characteristics
•Reduced vision in one eye
• Strabismus found on CT- usually not freely alternating
• No pathology detected on ocular examination

• Occurs in 5-8% of general population
• The risk is 4x greater if one parent has strabismus
• 65% of patients impacted have a close relative with strabismus

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13
Q

Anisometropic amblopia:

A

• Significant anisometropia present (At least 1D difference)
• Clearer vision in one eye for all distances
• Can be mostly spherical or mostly astigmatic

• Hypermetropia:
Most common

• Meridional (astigmatism):
Oblique astigmatism: more likely myopic

• Myopia
Can be avoided if one eye clear for distance and one clear for near

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14
Q

Stimulus deprivation amblyopia:

A

• Stimulus form vision deprivation amblyopia
• One or both eyes
• Little or no light enters the eye.

• Congenital Cataract- most common
• Ptosis
• Haemangioma
• Vitreous Opacity e.g., bleeding
• Corneal Scar

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15
Q

Meridional Amblyopia:

A

•Moderate-high degree of uncorrected astigmatism
•Can be unilateral or bilateral
•More significant risk in oblique astigmatism

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16
Q

Ametropic Amblyopia

A

•Likely bilateral
• High degree of bilateral refractive error goes uncorrected during critical period
•Blurred vision in both eyes at all distances.
• Typically, a result of high bilateral hypermetropia 6D or greater (Cannot be compensated using accommodation)

17
Q

Organic Amblyopia: types

A

• Reversible
- Toxic Amblyopia (not always reversible)

• Irreversible
Not able to be treated. No lesion
- Nystagmus
- Albinism (usually associated with nystagmus)

18
Q

Toxic Amblopia:

A

• Painless, progressive, bilateral vision loss
• Dyschromatopsia
• May also be referred to as “toxic optic neuropathy”

• Nutrional Amblyopia
- Vitamin B12 deficiency
- Seen in patients with extreme diets- reports in patients with ASD
- May see complete/incomplete recovery with improved diet/vitamin intake

• Other common causes
- Alcohol- may be associated with B12 deficiency
- Tobacco
- Antimalarials e.g., Chloroquine
- Anticancer treatments e.g., Vincristine

19
Q

Investigations for amblopia:

A

Case History- Family history of childhood eye problems!
• Ocular Examination- Assess media and fundus
• Full Cycloplegic Refraction
• Visual Acuity Assessment: age and ability appropriate test selection
• Cover Test- is there a manifest deviation? What is the fixation preference/pattern?
• Contrast Sensitivity: Amblyopes can have reduced contrast sensitivity at higher spatial frequencies in comparison to non-amblyopes
• Uniocular fixation
• 4^ Test

20
Q

Assessment of Uniocular Fixation

A

• Assess the point of the retina that the patient is using for fixation when the other eye is occluded
• Using a visuscope or ophthalmoscope

Method:
• Dim room lights
• Ask patient to fix at distance
• Occlude “fellow normal eye”
• Line up instrument
• Get patient to fix on centre of light
• Assess where the “bright” reflex is positioned

21
Q

What can be the 3 findings when assessing the uniocular fixation?

A
  • Central fixation
  • Eccentric fixation
  • Wandering fixation
22
Q

Central fixation and wandering fixation:

A

Central Fixation
o Object on fovea

Wandering fixation
o Uniocular condition
o Fovea has lost its fixation superiority, and no single area of the retina is used for fixation

23
Q

Eccentric Fixation

A

o Uniocular condition. Fixation is by a point which isnt the fovea.
o This point is the principle visual direction.
o The degree of eccentric fixation is defined by the distance between the fovea in degrees.
o The further from the fovea= worse the level of VA
o Estimated line reduces by 1 line per 0.5 degrees of eccentricity

24
Q

Management of Amblyopia

A

• Patients are prescribed their full refractive correction for full time wear.
• Correction of refractive error results in resolution of anisometropic amblyopia in 1/3 of 3–7 year olds
• Resolution of amblyopia in 32% of patients with strabismic and combined strabismic+ anisometropic amblyopia. Better results in strabismic only versus combined
• Refraction adaptation mostly complete by 18 weeks
• 90% have resolution by 18 weeks of refractive adaptation
• Improvement can continue for up to 30 weeks

25
Q

Occlusion Treatment

A

Occlude the non-amblyopic eye to encourage used of amblyopic eye stimulating visual development.

Types of Occlusion:
• Total Occlusion- excludes light and form vision e.g., sticky patch or fabric
patch.
• Total Occlusion- excluded form vision e.g., allows some light passage e.g.,
blenderm tape.
• Partial Occlusion- some form vision but reduces acuity e.g., Bangerter foils
Compliance has been reported to vary from 49%-87%

26
Q

How Many Hours for occlusion?

A

• Moderate Amblyopia: 0.300-0.600
- 2 hours-6 hours when combined with 1 hour of near visual activities in children <7 years
- Begin with 2 hours and if no significant improvement, increase to 6 hours.

• Severe Amblyopia: 0.700 or worse
- Full time occlusion (all waking hours or all but one)
- Part time occlusion: Set hours per day
In patients with strabismic, anisometropic and combined….results of 6 hours of occlusion= full time in children ages 3-7 years

27
Q

Risks of Occlusion

A
  1. Intractable Diplopia:
    • Rare
    • Strabismic amblyopia
    • Higher risk in older children
    • Sbisa bar (density of suppression) assessed to monitor throughout treatment
    • Occlusion immediately stopped
    •Patients can re-suppress
  2. Amblyopia develops in the other eye- rare in part time occlusion
  3. Dissociation in decompensating strabismus
  4. Allergic reaction:
    Skin reaction in conventional occlusion
    Allergy to atropine- local or systemic
28
Q

Atropine Penalisation

A

• Atropine is instilled (long-lasting cycloplegic agent) into the sound eye, preventing accommodation and blurring vision at near fixation.
• Instilled daily or two consecutive days per week same results.
• Switch of fixation- even if periodically!
• Generally high rates of compliance.
• Useful in mild-moderate amblyopia in patients aged 3-7 years
• Conflicting evidence for its use in severe amblyopia- some reports of significant improvement

29
Q

Atropine Penalisation pros and cons

A

Pros:
• Patients may be resistant to patch on face e.g., Sensory issues
• Useful if patients allergic to patch- can peek from fabric patch!
• Some children don’t like the appearance of the patch

Cons:
• Light sensitivity
• Risk of allergic reaction to drop
• Reported to cause nightmares

30
Q

Optical Penalisation used when:

A

• Prescription is manipulated/lenses used to blur the vision in better seeing eye- encouraging use of the amblyopic eye.
- Can be used on its own or in combination with atropine.

When is it used?
o When cooperation with patching is poor or non-existent.
o Patients with latent nystagmus.
o No improvement with other treatment.
o When atropine alone is not enough to reduce acuity sufficiently.

31
Q

Optical Penalisation Types

A

• Distance Penalisation: +3.50DS added to non-amblyopic eye

• Near Penalization: Cycloplegia in the non-amblyopic eye with full correction and a hypermetropic lens (up to 3.00DS) in the amblyopic eye.

• Total Penalisation: High hypermetropic lens added to non-amblyopic eye to induce blur at both near and distance.

(1) Concomitant Strabismus and Visual Development (16 decks)

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