Consequences of squint and amblyopia Flashcards
What type of diplopia is caused by exotropia and why?
Crossed
Image falls on temporal retina, so seen in nasal field
What type of diplopia is caused by esotropia and why?
Uncrossed
Image falls on nasal retina, so seen in temporal field
What is confusion?
Two objects seen in the same place during diplopia (uncommon), due to fovea of deviated eye seeing different image to straight eye
What is suppression?
Mental inhibition of one eye to favour image from the other eye when both eyes open.
What does foveal suppression avoid and how dense is it?
Confusion
Very dense
What does peripheral suppression avoid and how dense is it?
Diplopia
Less dense than foveal suppression
What is a suppression scotoma?
Measurable area of suppression (area between foveal and peripheral suppression)
How can suppression be measured?
Sbisa bar
Assesses risk of intractable diplopia development
How does a Sbisa bar work?
Shows 17 filters of varying red colours, allowing less illumination and forcing suppressed eye to fixate - able to find the diplopic point (px reports diplopia).
Lighter filter = less dense
What is a definition of amblyopia?
Reduced VA in one eye not caused by any pathology of the visual pathway and isn’t corrected by refractive correction.
What are the types of amblyopia?
Stimulus deprivation
Anisometropic
Meridional
Strabismic
Ametropic
Idiopathic
Organic
What is stimulus deprivation amblyopia?
Due to occlusion by visual pathology e.g. ptosis, congenital cataract
What is strabismic amblyopia?
Suppression of deviated eye
(Alternating has equal VA)
What is meridional amblyopia?
Amblyopia in one meridian due to high astigmatism (in one eye)
What is anisometropic amblyopia?
Suppression of ‘weaker’ eye due to difference in refractive error
What is ametropic amblyopia?
Bilateral amblyopia due to uncorrected ametropia.
Needs FTW to improve VA
What is idiopathic amblyopia?
No known cause.
VA improves with occlusion
What is organic amblyopia?
Reduced VA due to lesion (detected or undetected).
Occlusion improves VA but not to normal.
What tests should be done to investigate amblyopia?
H&S
Refraction
Fundus and media
Corrected VA
10^ vertical prism test
CT
Ocular movements
Fixation assessment
Neutral density filter bar
Sbisa bar
Binocular function
What are the types of treatment available for amblyopia?
Occlusion of better eye
Optical penalisation
Total penalisation
Cycloplegic drugs
What are the types of occlusion therapy?
Total: exclude light and form (patch on skin) or just form (patch on specs)
Partial: diminished form appreciation allowed (translucent materials used)
What are the types of optical penalisation?
Distance: over correct better eye
Near: use cyclo on better eye and give amblyopic eye plus lens to encourage use at near
Total: very strong lens for better eye, force amblyopic eye to work at all distances
How does cycloplegia work in amblyopia treatment?
Used in better eye to blur
Usually used when poor patch compliance
Unlikely to work for dense amblyopia (not blurred enough)
Needs regular clinic attendance due to risk of reversal
What are the indications for the type and duration of amblyopia treatment?
Level of vision
Age
Duration of squint
Intermittent/latent squint (partial occlusion more likely to avoid decomp)
Latent nystagmus (cyclo more likely to be used)
