Skleral

Skleral refers to the sclera, the tough, opaque outer coat of the eyeball. The sclera forms most of the globe’s outer layer, surrounding the intraocular contents except where the cornea covers the anterior surface. It is composed mainly of dense irregular connective tissue rich in type I collagen, providing mechanical strength and helping to maintain the eye’s shape. Thickness varies by region, typically about 0.3 to 1.0 mm, being thicker posteriorly and thinner near the equator. The sclera is relatively avascular; nourishment comes primarily from the choroid and from vessels in the overlying episclera.

The boundary with the cornea at the limbus marks the transition between sclera and corneal tissue. The sclera serves as an anchor for the extraocular muscles and acts as a protective capsule for the internal ocular structures. Its opaque nature contributes to the white appearance of the eye.

Clinical relevance: Inflammation of the sclera is called scleritis, while inflammation of the more superficial episclera is termed episcleritis. Conditions that thin or weaken the sclera include high myopia, scleromalacia, and certain connective tissue disorders such as osteogenesis imperfecta. In retinal surgery, scleral buckling procedures place implants against the sclera to support the retina. Imaging techniques such as ultrasound, ultrasound biomicroscopy, and magnetic resonance imaging can assess scleral thickness and integrity in various conditions.

Etymology: The term derives from the Greek skleros, meaning “hard.” The adjective skleral is used to describe structures or conditions related to the sclera.