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 afferent visual pathway
  • Most common cause of vision loss in children
  • Interruption of normal visual development
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2
Q

What are the 2 mechanisms of amblyopia?

A
    1. Deprivation of Form Vision
      o Can be partial or complete
      o Complete: No image/stimulus reaches fovea
      o Partial: Degraded imaging reaching fovea
    1. Abnormal Binocular Interaction
      o Incomplete images fall on the retina – something disrupting light getting to retina e.g. cataract
      o Images are incompatible
      o Eyes compete for control over cortical connections during development period- better eye gains control – one eye sees well and one eye doesn’t so competing
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3
Q

What does amblyopia look like to us?

A
  • Reduced Snellen and grating acuity
  • Loss of contrast sensitivity – big factor in amblyopia
  • Shape distortion
  • Motion deficits – don’t appreciate motion as much
  • Crowding effect
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4
Q

What are the 4 aspects of visual function? Describe them?

A
  1. Light Sense
    o Most primitive
    o Ability to disntinguish light & dark
    o Rods
  2. Form Sense
    o Ability to distinguish between spatially separate visual stimuli
    o Ability to discern size and shape of objects
    o Position and orientation
    o Rods and cones
    o Most acute at fovea
  3. Colour Sense
    o Distinguish between light of different wavelengths
    o Cones
  4. Motion Sense
    o Ability to detect movement of images across retina
    o Visual cortex
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5
Q

What are the periods of visual developmetn (Birth to 8/9)?

A
  • Critical period: a few months old – approx. 5yrs old. Deprivation causes damage
    o Period with active neural plasticity (ability of the neural system to undergo change).
    o Period where deprivation impacts visual development and amblyopia can develop.
    o Amblyopia can only develop within this time.
    o Earlier the onset of deficit + the longer the period of deprivation= worse the outcome
  • Sensitive period: time of deprivation – teenager years (some evidence in adult cases too).
    o Amblyopia less likely to occur but improvement possible
    o Improvement is possible during this time.
    o The younger the patient= the quicker the response to treatment.
    o Less common after 8 years of age
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6
Q

What are the types of amblyopia?

A
  • Functional – improvement after tx is expected
    o Strabismic – most common
    o Anisometropic – most common
    o Stimulus Deprivation
    o Meridional
    o Ametropic
  • Organic – no lesion, may be reversible or irreversible
    o Toxic
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7
Q

Describe strabismic amblyopia?

A
  • Result of constant or near-constant childhood strabismus in one eye.
  • Mostly esotropias as many exotropia’s are intermittent in childhood
    o XOT can become constant into adulthood
  • Clinical Characteristics
    o Reduced vision in one eye
    o Strabismus found on CT- usually not freely alternating (one specific eye is turned)
    o No pathology detected on ocular examination
     Need to rule out other problems in media, retina etc as that would not be amblyopia
    o Occurs in 5-8% of general population
    o Risk is 4x greater if one parent has strabismus
    o 65% of patients impacted have a close relative with strabismus
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8
Q

Describe anisometropic amblyopia?

A
  • Significant anisometropia present (At least 1D difference)
  • Clearer vision in one eye for all distances
  • Can be mostly spherical or mostly astigmatic
  • Hypermetropia:
    o Most common as never clear at any distance
  • Meridional (astigmatism):
    o Oblique astigmatism: more likely myopic
  • Myopia:
    o Can be avoided if one eye clear for distance and one clear for near
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9
Q

Describe stimulus deprivation amblyopia (SDA)?

A
  • Stimulus form vision deprivation amblyopia
  • Difficult to treat
  • One or both eyes
  • Little or no light enters the eye.
  • Congenital Cataract- most common – bilateral cataract prognosis is not v good
  • Ptosis – if fully covers pupil then amblyopia more likely to develop as less light getting in
  • Haemangioma
  • Vitreous Opacity e.g., bleeding
  • Corneal Scar
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10
Q

Describe meridional amblyopia?

A
  • Moderate-high degree of uncorrected astigmatism
  • Can be unilateral or bilateral
  • More significant risk in oblique astigmatism
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11
Q

Describe ametropic amblyopia?

A
  • Likely bilateral
  • High degree of bilateral refractive error (likely hyperopia) 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)
  • Most children are able to get up to level of driving standard – but some don’t reach this level
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12
Q

Describe reversible organic amblyopia?

A
  • Reversible
    o Toxic amblyopia – not always reversible – often associated w/ optic nerve dysfunction
     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
    o But vision may not be back to full level
    o May see in children with autism spectrum disorder: they have safe foods due to sensory issue but if rest of vitamins are not supplemented in their diet then they may develop this
     Other common causes
  • Alcohol- may be associated with B12 deficiency
  • Tobacco
  • Antimalarials e.g., Chloroquine
  • Anticancer treatments e.g., Vincristine
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13
Q

Describe irreversible organic amblyopia?

A
  • Irreversible
    o Not able to be treated – no lesion
     Nystagmus – never get a clear image so cannot develop good vision
     Albinism (usually associated w/ nystagmus)
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14
Q

What are the investigations for amblyopia?

A
  • Case History- Family history of childhood eye problems
    o Surgery, patching, spex – if no one in close family ask about cousins, aunties, uncles
  • 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- Very useful tool!
    o Amblyopes can have reduced contrast sensitivity at higher spatial frequencies in comparison to non-amblyopes
  • Uniocular fixation – do they use the fovea to fix or a different point?
  • 4^ Test
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15
Q

Describe 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 visuscope or ophthalmoscope
  • Method:
    o Dim room lights
    o Ask patient to fix at distance
    o Occlude “fellow normal eye”
    o Line up instrument
    o Get patient to fix on centre of light
    o Assess where the “bright” reflex is positioned
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16
Q

What is the management of refractive amblyopia?

A
  • Refractive Amblyopia:
    o Patients are prescribed their full refractive correction for full time wear (only removed for bed & bath)
    o Correction of refractive error results in resolution of anisometropic amblyopia in 1/3 of 3–7-year-olds (PEDIG, 2006) (Asper et al., 2018)
    o Resolution of amblyopia in 32% of patients with strabismic and combined strabismic+ anisometropic amblyopia. Better results in strabismic only versus combined (PEDIG, 2012)
    o Refraction adaptation mostly complete by 18 weeks (Stewart et al., 2004)
    o 90% have resolution by 18 weeks of refractive adaptation (PEDIG, 2012).
    o Improvement can continue for up to 30 weeks (PEDIG, 2006)
     GET PX TO WEAR GLASSES FOR 4 MONTHS (18 WEEKS) – don’t want to start patching before full refractive adaptation
17
Q

Describe occlusion tx? Types? How many hours?

A
  • Occlude the non-amblyopic eye to encourage used of amblyopic eye which stimulates visual development.
  • Types of Occlusion:
    o Total Occlusion- excludes light and form vision e.g., sticky patch or fabric patch.
     Sticky is best as child may peak under fabric patch
    o Total Occlusion- excluded form vision e.g., allows some light passage e.g., blenderm tape.
    o Partial Occlusion- some form vision but reduces acuity e.g., Bangerter foils
  • Compliance has been reported to vary from 49%-87% (Stewart et al., 2004).
    o Depends on parent encouragement, allergy to patch, how bad other eye is, learning disabilities
  • How Many Hours:
    o Moderate Amblyopia: 0.300-0.600
     2 hours=6 hours when combined with 1 hour of near visual activities in children <7 years (PEDIG, 2003)
     Begin with 2 hours and if no significant improvement, increase to 6 hours.
  • No more than 6hours a day
  • Find out what works for family – if vision 0.9 then they are losing work as cant see in school – if px gets up early enough can do 2 hours in morning and 4 hours in evening
    o Taking patch off child is worst thing – as super sticky
    o 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 (PEDIG, 2004)
18
Q

What are 4 risks of occlusion?

A
    1. Intractable Diplopia:
      o Rare
      o Covering good eye, child using other eye they have suppressed, they then overcome the suppression and get diplopia
      o Strabismic amblyopia
      o Higher risk in older children (8/9yo) – monitor px
      o Sbisa bar (density of suppression) assessed to monitor throughout treatment
      o Occlusion immediately stopped – parent remove patch immediately and phone clinic
      o Patients can re-suppress
    1. Amblyopia develops in the other eye- rare in part time occlusion
    1. Dissociation in decompensating strabismus – px has BSV – the eyes aren’t fusing – end up with manifest squint
    1. Allergic reaction:
      o Skin reaction in conventional occlusion
      o Allergy to atropine- local or systemic
19
Q

Describe atropine penalisation? (not for entry-level optoms)

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.
    o E.g. Saturday morning & Sunday morning – lasts the week
  • Switch off fixation- even if periodically!
  • Generally high rates of compliance.
  • Useful in mild-moderate amblyopia in patients aged 3-7 years (PEDIG, 2002)
  • Conflicting evidence for its use in severe amblyopia- some reports of significant improvement (PEDIG, 2009)
    o Sometimes eyes don’t switch fixation & keep using good eye as still not as blurred as poorer eye
  • Why is Atropine a good alternative?
    o Patients may be resistant to patch on face e.g., Sensory issues
    o Useful if patients allergic to patch- can peek from fabric patch!
    o Some children don’t like the appearance of the patch
  • What are the downsides?
    o Light sensitivity
    o Risk of allergic reaction to drop
    o Reported to cause nightmares
20
Q

Describe optical penalisation?

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.
  • Distance Penalisation: +3.50DS added to non-amblyopic eye
  • Near Penalisation: 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.
  • When is it used?
    o When cooperation with patching is poor or non-existent.
    o Patients with latent nystagmus.
     When cover one eye it can get worse – so this is not physically covering eye (e.g. patching) then may not cause this
    o No improvement with other treatment.
    o When atropine alone is not enough to reduce acuity sufficiently.