he human eye detects radiation (or light) in a specific part of the spectrum we refer to as visible light. The normal human eye is capable of detecting an almost countless variety of colors within this spectrum. Our eyes can form images of objects either directly in front of us or as far as many miles away. Our eyes are so sensitive they can respond to a single photon of light. They can do this because of the high concentration of sensory receptors found in the eye. In fact, our eyes contain over 70% of all sensory receptors in the body. But the eye is only collecting and focusing light. It takes our brain to actually translate the messages the eye is perceiving to be able to “see” the world around us. Thus, to understand vision we must talk about how the eye, brain, and optic nerves all work together to visually interpret the world around us.
What we actually see are the patterns of light that strike the retina—a light-sensitive layer of cells at the back of the eye. In the center of the retina is the macula. The macula is where light is most focused and visual acuity, highest. Processing of visual information begins in the retina and macula. When light is focused through its lenses on these portions of the eye it triggers specific receptors to begin to fire. Depending on the specific color of light, or whether it is day or night, specific receptors initiate a cell-signaling cascade to occur. It is these cell signaling pathways that transmit signals from the eyes, through the optic nerves, and to the primary visual cortex of the brain, located at the very back of our head, that ultimately lead to us perceiving objects in the world around us.