The sclera, also known as the white of the eye, is the opaque, fibrous, protective, outer layer of the eye containing collagen and elastic fiber. In humans the whole sclera is white, contrasting with the coloured iris. It covers the eyeball The sclera is covered by the conjunctiva, a clear mucus membrane that helps lubricate the eye. It is thickest in the area surrounding the optic nerve. The sclera is made up of three divisions: the episclera, loose connective tissue, immediately beneath the conjunctiva; sclera proper, the dense white tissue that gives the area its color; and the lamina fusca, the innermost zone made up of elastic fibers.