The sclera is tough and fibrous, protecting the interior components of the eye from injury, and makes up the exterior coating of the eye. The sclera forms the entire visible white exterior of the eye, the iris is the colored portion of the outside of the eye.
The sclera is composed of four layers. The inside layer is called the endothelium, followed by the stroma, the lamina fusca, and the final outside layer is called the episclera.