The sclera refers to the white part in the eye. The anterior sclera only shows a small portion but 80 percent of the surface area of the eyeball is the sclera. A dense connective tissue forms the “white” in the eye or sclera.
There is a junction between the white sclera and clear cornea that is known as limbus. The thickness of sclera ranges from about 0.3 mm to 1.0 mm. The strength and flexibility of the eyeball depend on the connective tissue fibers that are arranged irregularly and interlacing.
The blood supply in the sclera is limited and it is inactive metabolically. The sclera is avascular which means it lacks blood vessels even though some blood vessels pass through the sclera.
Episclera is a thin and loose connective tissue layer on top of the sclera. The blood vessels in the episclera nourish the sclera and some come from the choroid under. The choroid is the layer of the eyeball that is between the sclera and retina.
Functions of Sclera
The shape of the eyeball is maintained with the sclera. Since sclera is fibrous and tough – it protects the eye from damage that can occur or from external trauma.
Another function of the sclera is it gives the extraocular muscles that control the movement of the eye a sturdy attachment.
Problems Affecting Sclera
Scleral icterus or icteric sclera refers to the condition when the white of your eye becomes yellow which can be associated with liver disease such as hepatitis.
If you have scleral icterus, the blood serum levels of bilirubin may be increased. If you develop yellowing of your eye, it is important to get tested to detect if you have scleral icterus or any associated liver problems.
Blue sclera refers to the condition when the normally white sclera turned into blue color. It usually occurs when your sclera is thinner than the normal thickness. The thinning of sclera allows the color of choroidal tissue to pass through.
Osteogenesis imperfecta and Marfan’s syndrome are congenital and hereditary diseases that can be associated with the blue sclera.
Episcleritis refers to the inflammation of the episclera. There are two forms of episcleritis which are nodular episcleritis and simple episcleritis. Most cases of episcleritis have an unknown cause but some cases have this eye condition and have a systemic disorder.
Scleritis refers to the inflammation of episclera and the underlying sclera. It is painful and more serious than episcleritis because it can cause permanent damage and vision loss.