The sclera is around 1 mm thick and has four layers: The sclera is made of collagen fibers. Collagen is a protein that is also found in your skin, muscles, bones, and connective tissue.

The sclera is the white external tunic that envelops the eye from the limbus or corneoscleral junction (anterior), and to the cribriform plate of the optic nerve head (posterior) (Figure 1).