Plasticity and restoration of vision after visual system damage: an update.

The traditional view that visual system damage is permanent has given way to a more optimistic view. Visual loss does not remain unchanged but it can recover spontaneously to some extent. Even when the period of spontaneous recovery has ended there is still additional potential for plasticity and regeneration, even months or years after the lesion. There are two fundamental approaches to harvest this plasticity potential: (i) to rescue dying cells or induce axonal regeneration of visual system neurons through biological (pharmacological) means and (ii) to capture the residual vision capacities and improve their functions by behavioural training. Visual training can be used to activate residual visual neurons either in the blind sectors of the visual field through alternative pathways or it can be used to activate partially damaged regions in the border zone near the lesion site. Another example of post-lesion neuroplasticity is the ability of the intact visual field sectors to (spontaneously) take over functions and this is seen, for example, in macular degeneration and even in developmental disorders, such as amblyopia who benefit from training even many years beyond the critical period. Just as plasticity after brain damage is well recognized in other functional systems (motor, somatosensory), plasticity of the visual system is now gradually being recognized as a useful mechanism whereby the brain compensates for its functional loss, either spontaneously or by repetitive visual stimulation.