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What is the structure of the cornea?

Diana Meeks
Diana Meeks on behalf of Sigma Nursing
Family Practitioner

Although the cornea is clear and seems to lack substance, it is actually a highly organized group of cells and proteins. Unlike most tissues in the body, the cornea contains no blood vessels to nourish or protect it against infection. Instead, the cornea receives its nourishment from the tears and aqueous humor that fills the chamber behind it. The corneal tissue is arranged in five basic layers, each having an important function. These five layers are:

Epithelium
The epithelium is the cornea's outermost region, comprising about 10 percent of the tissue's thickness. The epithelium functions primarily to (1) block the passage of foreign material, such as dust, water, and bacteria, into the eye and other layers of the cornea and (2) provide a smooth surface that absorbs oxygen and cell nutrients from tears and distributes these nutrients to the rest of the cornea.

Bowman's layer
Lying directly below the basement membrane of the epithelium is a transparent sheet of tissue known as Bowman's layer. It is composed of strong layered protein fibers called collagen. Once injured, Bowman's layer can form a scar as it heals.

Stroma
Beneath Bowman's layer is the stroma, which comprises about 90 percent of the cornea's thickness. It consists primarily of water (78 percent) and collagen (16 percent) and does not contain any blood vessels. Collagen gives the cornea its strength, elasticity, and form. The collagen's unique shape, arrangement, and spacing are essential in producing the cornea's light-conducting transparency.

Descemet's membrane
Under the stroma is Descemet's membrane, a thin but strong sheet of tissue that serves as a protective barrier against infection and injuries. Descemet's membrane is composed of collagen fibers (different from those of the stroma) and is made of the underlying endothelial cells.

Endothelium
The endothelium is the extremely thin, innermost layer of the cornea. Endothelial cells are essential in keeping the cornea clear. Normally, fluids leak slowly from inside the eye into the middle corneal layer (stroma). The endothelium's primary task is to pump this excess fluid out of the stroma.

This answer is based on source information from the National Institute of Diabetes and Digestive and Kidney Diseases.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.