In literature, television and film, the eyes are often imbued special meaning; the idea that you can tell something about a person, or what they are thinking or feeling, by gazing into their eyes. Eye colour is often considered a very straight-forward trait, with eyes being either brown, blue or green. But it is easily apparent that there is far more variation in human eye colour than that allows for, and that its inheritance is not always what one might expect. There are even some people out there who will try to convince you that your eye colour is controlled by diet. What really controls the appearance of our eyes? What are our eyes saying about us?
The mammalian eye, a refractive cornea non-compound eye, to be precise, is a wonderful example of the bizarre quirks of evolution that we see in nature. These are only really bizarre, of course, from the view-point of intelligent design.
Our visual system is made up of many tiny light receptors on our retina known as rods and cones. Each receptor picks up a small portion of light and relays the message to our brain via nerve connections in the optic nerve. Information from thousands of light receptors is pieced together by the brain to form an image of the world around us. The rest of the eye is designed to focus light onto the retina in the most efficient way possible. Logically, you would expect, therefore, that the eye would be designedso that nothing blocked light from reaching the retina. And yet, in the mammalian eye, the nerves and blood vessels connecting to the rods and cones protrude outwards in front of them. In order to connect back to the brain, the nerve fibres must then break through the wall of light receptors, creating a blind spot where they join the optic nerve.