scleras

The sclera is the opaque, white, fibrous outer layer of the eyeball. It is also commonly referred to as the white of the eye. The sclera provides structural integrity to the eye, maintaining its shape and protecting the delicate internal components. It is composed primarily of collagen fibers that are arranged in a dense, interwoven pattern, which contributes to its toughness and resistance to deformation.

The sclera covers approximately five-sixths of the eyeball's surface, with the anterior one-sixth being transparent and known as the cornea. The boundary between the sclera and the cornea is called the limbus. Tiny blood vessels are present on the surface of the sclera, which are responsible for its slight pinkish hue, particularly noticeable in individuals with lighter skin tones. The sclera is relatively avascular in its deeper layers.

Extrinsic muscles that control eye movement attach to the outer surface of the sclera. These muscles work in coordination to allow for a wide range of visual pursuits and fixations. The sclera is thinner in some areas, such as at the optic nerve exit, where it is known as the lamina cribrosa. This region allows the optic nerve fibers to pass from the retina to the brain. Conditions affecting the sclera can range from inflammation, known as scleritis, to thinning or changes in coloration, which can sometimes indicate underlying systemic health issues.