See also: Chiasma (homonymy)

The optical chiasma allows the Décussation of a certain number of axons coming from the Rétine, i.e. their change on side to ensure the cross treatment of the visual information. It is thus the place of the gathering of the visual informations of same a hémichamp visual collected by the two retinas.

Within each Optical nerve, the axons coming from the nasal side of the retina will change side at the optical level it chiasma to make so that the left half of the field of vision is treated by the cerebral hemisphere right, and vice versa. Indeed, the visual informations are projected in mirror reversed in the eye so that the image of the periphery Ipsilatéral E of the field of vision is formed on the part Médial E of the retina (in blue on the figure opposite) while the image of the part ipsilatérale médiale of the field of vision is projected on the side part of the retina, located side of the temples (in red on the figure). As the axons coming from this part of the retina transport already information of the opposite field of vision (Contralatéral), they do not need to change side and continue straight in the optical Tractus towards the visual Cortex ipsilatéral, via the side geniculate Corps.