The sclera is the dense connective tissue of the eyeball that forms the “white” of the eye. It is continuous with the stroma layer of the cornea. The junction between the white sclera and the clear cornea is called the limbus.
Here are a few conditions that can affect the sclera:
Scleral icterus (yellow eyes). This condition — also called icteric sclera — is a yellowing of the white of the eye. It is associated with hepatitis and other liver disease.
Blue sclera. As you would expect, this condition is when a normally white sclera has a somewhat blue color. Blue sclera is caused by a congenitally thinner-than-normal sclera or a thinning of the sclera from disease, which allows the color of the underlying choroidal tissue to show through it.
Episcleritis. This is inflammation of the episclera that lies atop the sclera and under the conjunctiva. Episcleritis is relatively common and tends to be benign and self-limiting. It has two forms: nodular episcleritis where the redness and inflamed tissue occurs on a discrete, elevated area overlying the sclera, and simple episcleritis, where dilated episcleral blood vessels occur without the presence of a nodule.
Scleritis. This is inflammation of both the episclera and the underlying sclera itself. Scleritis is a more serious and typically more painful red eye than episcleritis. Up to 50 percent of cases of scleritis involve an underlying systemic disease, such as rheumatoid arthritis.