Brain's visual pathways. Illustration of the visual pathways from the eyes (top) to the visual cortex of the brain (bottom). Nerve impulses produced when light falls on the retinas of the eyes travel along the optic nerves from each half of the retina (red, outer half; and blue, inner half). The impulses travel via the chiasma (crossing point of the optic nerves). The nerve impulses from the right-hand sides of the retinas end up in the right-hand side of the brain, while nerve impulses from the left-hand side end up in the left-hand side of the brain. This is achieved by a crossing of the impulses from the internal halves of the retina (blue pathways). The impulses from the outer halves of the retinas do not cross (red pathways). The nerve impulses are processed in the brain to create a coherent image of what is seen by the eyes. Feedback from the brain (green pathways) controls the muscles that adjust the lens, allowing for the images to be focused.