sclerae

The sclerae, or sclera, are the opaque, fibrous outer coat of the eyeball. They enclose and protect intraocular structures and give the eye its shape. The sclera is composed mainly of dense irregular connective tissue rich in collagen fibers (predominantly type I), with proteoglycans and relatively few cells. The collagen lamellae run in multiple directions, providing strength and opacity. The anterior sclera blends with the corneal stroma at the limbus; the posterior sclera is thicker and forms the wall of the globe behind the retina, including the region around the optic nerve head where the lamina cribrosa lies.

Vascular supply to the sclera is limited; nutrients reach it from the episclera, choroid, and surrounding tissues by diffusion. Innervation is provided by branches of the ophthalmic nerve, including the long and short posterior ciliary nerves, making the sclera sensitive to pain and pressure.

Functions include maintaining ocular shape, protecting intraocular contents such as the lens, vitreous, and retina, and providing attachment points for extraocular muscles. The sclera is continuous with the cornea at the limbus, forming a protective enclosure for the globe.

Clinical notes: scleral thinning or deformation can occur with high myopia, aging, or scleromalacia. Inflammation of the sclera causes scleritis, often linked with systemic autoimmune disease; episcleritis is a milder inflammation of the overlying episclera. Blue sclera can occur with thinning (as in osteogenesis imperfecta); yellow sclera can indicate jaundice.