Amblyopia Flashcards
What is amblyopia
- reduction in vision In one or both eyes
- persistent after correction
- absence of retinal pathology or any disease
- most common cause of visual loss in children
- interruption of normal development
What can cause amblyopia
- deprivation of form vision
- abnormal binocular vision
What is depravation of form vision
- can be partial or complete
- complete: no image/stimulus reaches fovea
- partial: degraded imaging reaching fovea
What is abnormal binocular vision
- incomplete images fall on retina
- images are incomparable
- eyes compete for control over cortical connection during developmental period
Effects of amblyopia
- reduced snellen and grating acuity
- loss of contrast sensitivity
- shape distortion
- motion deficits
- crowding effect
4 factors of visual function
- light sense
- form sense
- colour sense
- motion sense
What is light sense
- ability to distinguish light and dark
What is 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
Which region is responsible for motion sense
- visual cortex
Periods of visual development
- critical period
- sensitive period
What is the critical period
- period with active neural plasticity
- deprivation impacts visual development
- amblyopia can only develop in this time
- earlier onset = longer the period of deprivation = worse outcome
What is the sensitive period
- improvement is possible
- teenage years
- younger Px = quicker response to treatment
Effects of strabismus (on LGN and cortex)
- high number of monocular cells
- loss of stereoscopic vision, causing abnormal visual cortex
- alternating strabismus results in an equal no. Of cells for R+L and virtually no binocularly driven cells
- reduced retinal ganglion cell layer & LGN
Classifications of amblyopia
- functional
- no lesion
Types of functional amblyopia
- strabismic
- anisometropic
- stimulus deprivation
- meridional
- ametropic
Types of no lesion amblyopia
- organic
- toxic
What is strabismic amblyopia
- constant or near constant childhood strabismus in on eye, mostly esotropes as exotropes are intermittent
Clinical characteristics of strabismus amblyopia
- reduced vision in one eye
- strabismus found on CT, usually not alternating
- no pathology detected on ocular examination
- occurs in 5-8% of general population
- 4x greater risk if strabismic relative
- 65% of Px have strabismic relative
What is anisometropic amblyopia
- significant anisometropia present
- hypermetroia - most common
- meridional - oblique astigmatism, more likely myopic
- myopia - can be avoided if one eye clear for distance and one clear for near
What is stimulus depravation amblyopia
- one or both eyes
- little or no light enters the eye
What causes stimulus deprivation amblyopia
- congenital cataract
- ptosis
- haemangima
- vitreous opacity
- corneal scar
What is meridional amblyopia
- moderate - high degree of uncorrected astigmatism - can be unilateral or bilateral
- more significant risk in oblique astigmatism
What is ammetropic amblyopia
- 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 more
What is Organic amblyopia
Reversible - toxic amblyopia
Irreversible
- can’t be treated
- nystagmus
- albinism
What is Toxic amblyopia
- painless, progressive, bilateral vision loss
- dyschromatopsia
- may also be referred to as toxic optic neuropathy
What is nutritional amblyopia
- vitamin B12 deficiency
- extreme diet, such as Px with ASD
- may be complete/incomplete recovery with improved diet/vitamin intake
What else causes nutritional amblyopia
- alcohol
- tobacco
- antimalarials
- anti cancer treatments
Investigations for amblyopia
- case history
- ocular examination to assess fundus
- full cycloplegic refraction
- VA assessment
- cover test
- contrast sensitivity
- uniocular fixation
- 4 dioptre test
Assessment of uniocular fixation
- assess the point of the retina that the Px is using for fixation when the other eye is occluded
- using ophthalmoscope
Methods of Management of amblyopia
- refractive adaptation
- occlusion treatment
- atropine
- optical penalisation
What is refractive adaptation
- prescribed full refractive correction for full time wear
- resolution of anisometropic amblyopia in 1/3 of 3-7 yr olds
- resolution of amblyopia in 32% of Px with strabismic & combined strabismic and anisometropic amblyopia
- refraction adaptation mostly complete by 18 weeks
- 90% have resolution by 18 wks of refractive adaptation
- improvement can continue for up to 30 weeks
What is occlusion treatment
- occlusion of non amblyopia eye
Types of occlusion
- total occlusion
- partial occlusion
What is total occlusion
- excludes light and form vision
- excludes form vision
What is partial occlusion
- some form vision but reduced acuity
How long should Px be occluded - moderate and severe
Moderate - 2/6 hours
Severe - full time
Risks of occlusion
- intractable diplopia
- amblyopia in other eye
- dissociation in decompensating strabismus
- allergic reaction
What is atropine penalisation
- prevents accommodation, and blurring vision at near fixation
- instilled daily or 2 consecutive days per week
- high compliance rate
Why is atropine a good alternative
- may be resistant to patch
- allergic to patch
- appearance of patch
Downsides of atropine
- light sensitivity
- risk of allergic reaction
- nightmares
What is optical penalisation - and types
- rx manipulated to blur vision in better eye
- can be used on its own or with atropine
- distance penalisation - +3.50 added
- near penalisation - cyclo in non amblyopia eye with full correction and hypermetropic lens in amblyopic eye
- total penalisation - high hypermetropic lens added to non amblyopic eye
When is optical penalisation used
- when cooperation with patching is poor
- latent nystagmus
- no improvement with other treatment
- atropine alone not enough
