BVP - Strabismus Assessment IV: Amblyopia - Week 12 Flashcards
Define amblyopia.
Reduction in visual capacity of one or both eyes not improved by refractive correction and occurs in the absence of ocular or visual pathway pathology
What can amblyopia result in the loss of?
Hand-eye coordination
hat is one of the most common forms of visual impairment in the world?
Amblyopia
Is amblyopia cheap to rehabilitate?
Yesd
During the post-natal refining process, what percentage of the striate cortex receives binocular input?
80%
What is meant by the sensitive period?
The time when amblyopia can occur.
Describe how the post-natal refining process can be susceptible to amblyopia.
The reliance of the developing visual system on visual input makes it susceptible to abnormal input even if temporary
When is the sensitive period?
From birth to ~7 yoa and up to 11-12 yoa
List three mechanisms of amblyopia development.
Deprivation of form visiond
Abnormal binocular interaction
Both
Describe deprivation of form vision and what it leads to neurologically.
When one eye is deprived of form vision, such as by anisometropia or cataracts, that eye will have a poorer image in the striate cortex and will not compete with the other eye’s image
Thus the axons of the eye with no form deprivation will take over the binocular cells
What happens in the striate cortex during visual development?
It receives input from both eyes, which will compete for striate cortex space
If balanced there will be no amblyopia
List two possible causes of deprivation of form vision.
Cataracts
High refractive error (including anisometropia)
List two causes of abnormal binocular interaction.
There is a different image at corresponding points (strabismus)
If the relative clarity is different (unilateral cataract or anisometropia)
Can strabismus result in form vision deprivation?
No
Can high bilateral refractive error result in abnormal binocular interaction?
No
Can bilateral cataract result in abnormal binocular interaction?
No
Define amblyogenic factor.
A condition that will cause amblyopia if present during the sensitive period
Describe how anisometropia is an amblyogenic factor.
Refractive blur in one eye causes the neural signals from that eye to be weaker than the signals from the other eye
What does the strength of neural signals from our eyes depend on?
Contrast, not absolute light levels
Describe how strabismus is an amblyogenic factor.
Diplopia is confusing and results in the suppression of some of the information from one eye
Describe why suppression occurs with strabismus.
Diplopia is confusing and suppression is the most efficient way to deal with it
Is suppression a monocular or binocular adaptation?
Binocular
Does suppression involve the entire visual field of an eye?
No
How are amblyopia and suppression related?
Amblyopia is a monocular sequelae to suppression
Describe visual deprivation.
Physical blockage that stops the formation of a clear retinal image
List 4 examples of visual deprivation.
Congenital or traumatic cataracts
Corneal opacities
Complete ptosis
Resolved perinatal macular haemorrhage
Will the clinical sign of visual deprivation always persist? Explain.
The clinical sign may no longer exist (may need to be a diagnosis of exclusion)
What is meant by orgnic amblyogenic factors?
Subtle, sub-ophthalmoscopic morphological changes or dietary insufficiencies
Explain the association of nystagmus to amblyogenic factors.
Some amblyogenic factors are secondary to nystagmus
May be an obvious nystagnmus
What is the most sensitive way to detect nystagmus?
Ophthalmoscopy - specifically visuoscopy
Consider younger and older children with amblyopia. How do they respond to treatment (4)?
Younger are typically
-quicker (faster acuity improvement)
-better (better final acuity)
-happier (better compliance)
-more complete (better binocular function)
How does amblyopia affect contrast sensitivity? Explain (2).
Reduced contrast sensitivity
-may be only at high spatial frequencies
-may be the entire CSF
How does amblyopia affect VA?
Reduced VA (D and N)
How does amblyopia affect spatial localisation?
Impaired (knowing where things are)
How does amblyopia affect visual processing speed?
Reduced
How does amblyopia affect binocular summation?
Reduced
How does amblyopia affect sensory fusion?
Reduced
How does amblyopia affect fixation?
Poor fixation
How does amblyopia affect eye movements (saccades and pursuits)?
Poor eye movements
Innacurate saccades
Jerky pursuits
How does amblyopia affect motor fusion? At worst, what is a consequence of this? At best?
Poor motor fusion
-at worst, strabismus
-at best, acc/verg disorder from reduced fusional vergence
How does amblyopia affect accommodative function (lag, NPA, facility)?
Poor accommodative function
-increased lag
-remote NPA
-reduced facility (monocularly)
Describe the treatment for amblyopia (4).
Provide a clear retinal image to the amblyopic eye
-glasses usually needed
Decrease the strength of the neural signals coming from the dominant eye
-an opaque patch or penalisation (atropine/translucent patch)
Treat any strabismus (motor and sensory)
Remove any other imediments to efficient binocular vision
-treat any residual accommodative dysfunction in the previously amblyopic eye
-treat visual inefficiencies
Consider sensory and motor aspects of strabismus. List the treatment options for each aspect (5/3).
Motor
-glasses
-surgery
-vision therapy
-prism
-a combination of the above
Sensory
-maintenance patching
-anti-suppression training
-both
