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 more complex schizochroal eye was found only in one sub-order of trilobite, the Phacopina (Ordovician-Silurian). It has no modern counterpart. The eye has up to 700 larger lenses with individual sclera separating each lens. Each lens has a cornea. Schizochroal eyes developed from holochroal ones and were more powerful with overlapping visual fields. They were particularly useful for nocturnal vision and possibly for colour and depth analysis. The lenses of the eye were constructed from single calcite crystals. Early schizochroal eye designs were rather haphazard and irregular, though constrained by the geometrical requirements of packing identical sized lenses on a