Vision

VISION

The visual system is largely represented by the eyes. Light waves enter the eye across the clear cornea and through the pupil, which is the opening to the eye itself. The cornea is the protective covering over the eye. The pupils will constrict or open in order to let more or less light into the eye. The iris is the colored part of the eye. There are muscles that increase or decrease the size of the pupil. Figure 15 shows the main structures of the human eye:

Figure 15.

Behind the pupil and iris is the lens. The lens is curved and is responsible for the focusing of objects. There are muscles that slightly change the shape of the lens so that a person can focus on near or far objects. Light from images is projected on the retina, which is the inner lining of the back of the eye. The retina is highly light sensitive and has photoreceptor cells. The cones are photoreceptors that work the best in bright lighting. They help to see details and color. The rods are not very color sensitive and are better able to function in low light settings. This is why color vision is so poor at night.