Sclera The sclera forms the "white" of the eye-ball. Like the cornea, the sclera is composed of collagen fibres, to form a hard, protective layer, however, unlike the cornea the collagen fibre are not arranged in a regular way. The sclera is pierced by numerous nerves and blood vessels and also provides the anchor point for the six extra-ocular muscles. The largest opening in the sclera, the posterior scleral foramen, is caused by the optic nerve.