Eyes

Our vision employs all the mechanisms that enable us to capture light, using our eyes, and to analyse this light using our brain. Considered to be the most highly developed sense in humans, our sight enables us to recognise almost 300,000 colours, as well as shapes, textures and contours in our surrounding environment.

The eye detects luminous energy in a process known as photoreception. It is approximately 2.5cm in diameter and made up of three layers, or tunics. The passage of light rays is facilitated firstly by an opening in the outermost layer, the cornea. The cornea itself plays a primarily protective role towards the exterior. The light then reaches the pupil, which dilates or contracts depending on the intensity of the light rays. The pupil is also an orifice, this time in the middle layer, and is surrounded by the iris, which gives the eye its colour. This second layer comprises another important structure that makes it possible to form an image on the retina, depending on the distance: the lens. The retina, therefore, forms part of the third, inner layer and is composed of sensory nerve cells. A distinction is made between two different types of photoreceptor cells: cones function in full light and make it possible to perceive colours, while rods function in weak light and perceive black and white. The inner layer of the eye comprises various areas, including the blind spot, where fibres come together to form the optic nerve that transmits visual information to the brain.

Without eyesight, food would be impossible to identify. The eye provides information on the state of food (liquid, solid), its appearance (shiny, matte), its colour, shape (round, oval, square) and its volume (small, large), etc. Eyesight makes it possible to identify food as good or bad, edible or toxic. What is more, pleasure for the eyes is inseparable from that experienced while eating. When the natural colour of food has been changed,  to a blue apple for example, it is no longer appetising. As far as apples are concerned, green is associated with an astringent, acidic taste and yellow with a sweet taste. Does well-formed fruit taste better? Cox’s orange pippins - splotchy, spotted and wrinkled - are nonetheless delicious!