A summary of the visual pathways in the brain is presented as a basis for considering abnormalities in this system. The role of the cortical associative regions in visual function is briefly delineated. A short summary of experiments describing plastic properties of the visual pathways at early age is also presented, and experiments describing neural and behavioural changes after binocular deprivation are reviewed. It is concluded that early visual deprivation leads to a profound alteration of the associative systems of the brain and that in monkeys and humans these changes are difficult to remedy later. Therefore early detection and correction of visual abnormalities is very important as well as early compensation using other forms of sensory communication.