Amblyopia

Question 1

What is amblyopia?

Answer 1

• 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

Question 2

What are the 2 mechanisms of amblyopia?

Answer 2

• 1. Deprivation of Form Vision
     o Can be partial or complete
     o Complete: No image/stimulus reaches fovea
     o Partial: Degraded imaging reaching fovea
• 2. 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

Question 3

What does amblyopia look like to us?

Answer 3

• 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

Question 4

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

Answer 4

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

Question 5

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

Answer 5

• 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

Question 6

What are the types of amblyopia?

Answer 6

• 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

Question 7

Describe strabismic amblyopia?

Answer 7

• 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

Question 8

Describe anisometropic amblyopia?

Answer 8

• 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

Question 9

Describe stimulus deprivation amblyopia (SDA)?

Answer 9

• 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

Question 10

Describe meridional amblyopia?

Answer 10

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

Question 11

Describe ametropic amblyopia?

Answer 11

• 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

Question 12

Describe reversible organic amblyopia?

Answer 12

• 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

Question 13

Describe irreversible organic amblyopia?

Answer 13

• 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)

Question 14

What are the investigations for amblyopia?

Answer 14

• 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

Question 15

Describe assessment of uniocular fixation?

Answer 15

• 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

Question 16

What is the management of refractive amblyopia?

Answer 16

• 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

Question 17

Describe occlusion tx? Types? How many hours?

Answer 17

• 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)

Question 18

What are 4 risks of occlusion?

Answer 18

• 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
• 2. Amblyopia develops in the other eye- rare in part time occlusion
• 3. Dissociation in decompensating strabismus – px has BSV – the eyes aren’t fusing – end up with manifest squint
• 4. Allergic reaction:
     o Skin reaction in conventional occlusion
     o Allergy to atropine- local or systemic

Question 19

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

Answer 19

• 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

Question 20

Describe optical penalisation?

Answer 20

• 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.