Competitive neuronal interactions underlying amblyopia.

Amblyopia, a Greek word meaning "blunt sight" refers to a common clinical condition characterised by lowered visual capacities in one or both eyes. Several different types of amblyopia have been defined and in the most common forms, strabismic and anisometropia amblyopia, one eye finds itself at a severe disadvantage relative to its counterpart. The evidence to be presented in this article will show that the reduction of visual capacities in one eye results from competition between binocular inputs rather than simply reflecting disuse of one eye. In addition, evidence will be represented to show that this binocular competition occurs in the visual cortex rather than in the periphery. In fact, there appear to be at least two separate levels of binocular competition within the visual cortex. Under most circumstances, it is possible to induce or to reverse amblyopia only during a well-defined sensitive period early in the life of the organism. With special efforts, however, prolongation of this sensitive period can be achieved and plasticity of cortical ocular dominance maintained into adulthood.