Improvement in amblyopic eye function and contralateral eye disease: evidence of residual plasticity

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Amblyopia is a visual deficit in which the retina appears normal. It is typically associated with strabismus and/or a refractive error, or an ocular opacity, all of which probably act by impeding visual development at a cortical level. Although the causal relations in amblyogenesis are not completely understood, a fundamental principle of treatment is that therapy can be effective only when the visual system is sufficiently plastic for cortical modification to occur. This epoch–the sensitive, or critical period of visual development–is age defined and thought to end at around 7 years. 1 Von Noorden GK Crawford MLJ The sensitive period. Trans Ophthalmol Soc UK. 1979; 99: 442-446 PubMed Google Scholar This tenet underpins the design of preschool vision-screening programmes, so that, at least in the UK, 2 Report of the Children's Sub-group of the National Screening Committee. Department of Health, London2000 Google Scholar all children at risk are identified at the latest by 5 years of age (ie, within this window of therapeutic opportunity). Once diagnosed, amblyopia is generally treated by occlusion therapy (patching of the fellow eye), which most clinicians believe to be effective (but disputed in a recent systematic review 3 Snowdon SH, Stewart-Brown SL. Preschool vision screening: results of a systematic review. CRD Report 9. York: NHS Centre for Reviews & Dissemination. Google Scholar ).