From the primary visual cortex visual information is spread to more than thirty cortical areas for specific 'higher' visual functions. There are two main directions of the flow of visual information, toward the parietal lobe as the dorsal stream and toward the inferotemporal lobe as the ventral stream.
Within the ventral stream are recognition functions, color perception, object background perception, whereas within the dorsal stream are functions like eye-hand coordination and orientation in space, both egocentric and allocentric space.
The visual system is a system of parallel pathways: In the eyes there are two sensory systems, cone cells for daylight vision and rod cells for twilight vision. In the optic nerves and visual pathways there are several different types of nerve fibres, of which the magnocellular and the parvocellular pathway are the most important. Visual information reaches cortical and subcortical visual functions via the retinocalcarine pathway or via the tectal pathway. From the primary visual cortex information flows either toward the parietal lobe as the dorsal stream or toward the temporal lobe as the ventral stream.
In an infant and a young child, visual impairment often delays all areas of development if early intervention does not take place. Among the areas of development that are the most important during the first year are:
- communication and interaction
- motor functions
- development of spatial concepts
- orientation in space, egocentric and allocentric
- development of object permanence and
- development of language
Later on development of social skills and self image is related to how peers and adults respond to the behaviors caused by the visual impairement. Many visually impaired children and teenagers experience communication and interaction as their most limited functional areas that therefore should receive intervention at an early age.