Amblyopia Flashcards
What is amblyopia?
- 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
What are the 2 mechanisms of amblyopia?
- Deprivation of Form Vision
o Can be partial or complete
o Complete: No image/stimulus reaches fovea
o Partial: Degraded imaging reaching fovea
- Deprivation of Form Vision
- 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
- Abnormal Binocular Interaction
What does amblyopia look like to us?
- 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
What are the 4 aspects of visual function? Describe them?
- Light Sense
o Most primitive
o Ability to disntinguish light & dark
o Rods - 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 - Colour Sense
o Distinguish between light of different wavelengths
o Cones - Motion Sense
o Ability to detect movement of images across retina
o Visual cortex
What are the periods of visual developmetn (Birth to 8/9)?
- 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
What are the types of amblyopia?
- 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
Describe strabismic amblyopia?
- 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
Describe anisometropic amblyopia?
- 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
Describe stimulus deprivation amblyopia (SDA)?
- 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
Describe meridional amblyopia?
- Moderate-high degree of uncorrected astigmatism
- Can be unilateral or bilateral
- More significant risk in oblique astigmatism
Describe ametropic amblyopia?
- 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
Describe reversible organic amblyopia?
- 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
Describe irreversible organic amblyopia?
- 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)
What are the investigations for amblyopia?
- 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
Describe assessment of uniocular fixation?
- 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
What is the management of refractive amblyopia?
- 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
Describe occlusion tx? Types? How many hours?
- 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)
What are 4 risks of occlusion?
- 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
- Intractable Diplopia:
- Amblyopia develops in the other eye- rare in part time occlusion
- Dissociation in decompensating strabismus – px has BSV – the eyes aren’t fusing – end up with manifest squint
- Allergic reaction:
o Skin reaction in conventional occlusion
o Allergy to atropine- local or systemic
- Allergic reaction:
Describe atropine penalisation? (not for entry-level optoms)
- 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
Describe optical penalisation?
- 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.