Sclera Sclera The sclera, also known as the white of the eye, is the opaque, fibrous, protective, outer layer of the human eye containing mainly collagen and some elastic fiber. In humans, the whole sclera is white, contrasting with the coloured iris, but in other mammals the visible part of the sclera matches the colour of the iris, so the white part does not normally show. In the development of the embryo, the sclera is derived from the neural crest. In children, it is thinner and shows some of the underlying pigment, appearing slightly blue. In the elderly, fatty deposits on
Arthropod eye curved surface. Later designs used graduating lens sizes. The third eye morphology of trilobites, called the abathochroal, was found only within the Eodiscina. This morphology consisted of up to 70 much smaller lenses. The cornea separated each lens, and the sclera on each lens terminated on top of each cornea. The eye morphology of trilobites is useful for determining their mode of life, and can function as palaeoenvironmental indicators. The horseshoe crab has traditionally been used in investigations into the eye, because it has relatively large ommatidia with large nerve fibres (making them easy to experiment on). It also falls