SENSE OF SIGHT

Your eyes sit in a hollow space in the skull and are protected by an eyelid and a bony eyebrow. The eye is covered with a transparent, curved cornea over a donut-shaped ring called the iris, which sits in the center of the white of the eye. The iris is the part that can vary from blue, to brown to hazel, which determines eye color. It's also the part of the eye where there are muscles that cause the pupil, the dark circle in the center, to enlarge or contract. 
It is through the pupil that light rays enter the eyeball. The size of your pupil changes depending upon the light available. Just behind the pupil is the lens. This is a transparent part of the eye which bends the rays of light and focuses the image on the back surface of the eyeball.