Functional and clinical anatomy of the visual system: An update with emphasis on the visual pathway and cortex

The visual system includes the eye, the visual pathway, and the visual cortex.Their integration supports the spectrum of visual functions: visual acuity, chromatic vision, stereopsis, and contrast sensitivity. However, the visual pathway and the cortex are responsible not only for the transmission and basic interpretation of visual stimuli, but for their perception and high-order association.The regional, systemic, and functional neuroanatomy of the visual system — particularly of the visual pathway and the cortex — is essential to understanding neuro-ophthalmological disorders. This is a review article on the functional and clinical anatomy of the visual system focused on the visual pathway and the cortex. Historical aspects are discussed, as well as the formation of the visual pathway and the primary and extrastriate visual cortex, and the corresponding clinical correlations with the retina, optic nerve, chiasma, optic tracts, and lateral geniculate nucleus (LGN), optic radiation, and visual cortex. The visual pathway originates at the retinal photoreceptors dividing into extra and intracerebral segments based on their position with respect to the LGN until its interconnection with the primary visual cortex. The retina, pathway, and visual cortex have a high level of organization and a high structural and functional retinotopic representation existing within several subsystems and connections of the visual system, and about 30 cortical zones, with specific activities that enable the phenomenon of vision. In general, visual pathway lesions affect the visual fields, and extrastriate cortical damages cause visual agnosias.