ScleraThe sclera, also known as the white of the eye, is the opaque, fibrous, protective, outer layer of the human eye, to which are attached extrinsic muscles for moving the eyeball. It contains mainly collagen and elastin. In children, it is thinner and shows some of the underlying pigment, appearing slightly blue. In the elderly, fatty deposits on the sclera can make it appear slightly yellow. Many people with dark skin have naturally darkened sclerae, the result of melanin pigmentation.
The human eye is relatively rare for having an iris that is small enough for its position to be plainly visible against the sclera.