The tough, leathery tissue that extends around the eye, protects it, and helps to keep its shape. It is made of white connective tissue containing collagen and elastic fibers that are produced by fibroblasts.
The visible front part of it is called the "white of the eye." At the very front of the eye, covering the iris and pupil, the sclera becomes, or is continuous with, the (transparent) cornea. The sclera is also continuous with the dura mater of the central nervous system.
The sclera is attached by tendons to the extraocular muscles, which move the eye to the left and right, up and down, and diagonally. It is separated from the underlying choroid by loose connective tissue and an elastic tissue network, the suprachoroid lamina.
An inflammation in the sclera is called scleritis and is characterized by a clearly confined red area in the white of the eye.