Most information about the external world enters the human mind via the visual system; when seeing and looking are impaired, important aspects of life may elude us or the world becomes disturbingly distorted. While the globe may be likened to a camera, it is the brain that constructs an image of the world. It does this by making sense of the signals it receives from the retina, in which it is helped by data stored in memory as well as data gathered through other modes of perception. The retinal signals, induced by photons hitting photoreceptor cells, travel fi rst by way of the optic nerves, optic.
