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
2
Q
What are the 2 mechanisms of amblyopia?
A
- 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
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
4
Q
What are the 4 aspects of visual function? Describe them?
A
- 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
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
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
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
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
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
10
Q
Describe meridional amblyopia?
A
- Moderate-high degree of uncorrected astigmatism
- Can be unilateral or bilateral
- More significant risk in oblique astigmatism
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
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
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)
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
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