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Amblyopia

  • Amblyopia

    • = vision development disorder in which an eye fails to achieve normal visual acuity, even with prescription eyeglasses or contact lenses

    • begins during infancy and early childhood

    • usually unilateral

      • also known as 'lazy eye'​

  • Irreversible & permanent reduction in visual acuity; can be unilateral or bilateral 

  • Response to anything that has reduced visual stimulation during development of the eye

    • can sometimes happen even without any apparent disease of the eye

  • Occurs because, in children (during sensitive period up to age 8-10 years), the visual pathways that connect the eye and brain are still developing, and are vulnerable to anything that causes poor vision 

    • it develops as an evolutionary protective mechanism​ - if one eye is not working well, the central nervous system / visual pathways develop in a way that suppresses the image produced by the bad eye

    • this reduces complications of having one bad eye i.e. double vision

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Causes of amblyopia

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  1. Strabismic amblyopia

    • The two eyes are not aligned; the eye that is deviated becomes 'lazy' i.e. the image is suppressed resulting in poor vision in this eye, as the brain is trying to prevent double vision 

  2. Ametropic amblyopia

    • occurs due to high refractive error in one / both eyes

    • more likely in hypermetropia (long sightedness)

  3. Anisometropic amblyopia

    • occurs when there is a difference in the refractive error between the eyes​

    • visual information from the eye with higher degree of refractive error is suppressed

  4. Stimulus deprivation amblyopia

    • happens because something is obscuring vision during childhood e.g. cataract, ptosis covering pupil

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Treatment of amblyopia

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  • Treat any identifiable causes

    • e.g. remove cataract, correct ptosis ​

  • Patching to occlude the good eye - forces use of the poor eye 

    • ​most effective treatment

    • ​can also use dilating drops to blur good eye - called 'penalisation', atropine used

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References

  • Salmon, J. F. (2019) Kanski’s clinical ophthalmology. 9th edn. London, England: Elsevier Health Sciences.

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