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Introduction

If your cornea becomes damaged through disease, infection, or injury, the resulting scars can interfere with vision by blocking or distorting light as it enters the eye.

The cornea is the clear, protective outer layer of the eye. Along with the sclera (white of the eye), it serves as a barrier against dirt, germs, and other particles that can harm the eye's delicate components. The cornea is also capable of filtering out some amounts of the sun's ultraviolet light.

The cornea also plays a key role in vision. As light enters the eye, it is refracted, or bent, by the outside shape of the cornea. The curvature of this outer layer helps determine how well your eye can focus on objects close-up and far away.

There are three main layers of the cornea:

• Epithelium: The most superficial layer of the cornea, the epithelium stops outside matter from entering the eye. This layer of the cornea also absorbs oxygen and nutrients from tears.
• Stroma: The stroma is the largest layer of the cornea and is found behind the epithelium. It is made up mostly of water and proteins that give it an elastic but solid form.
• Endothelium: The endothelium is a single layer of cells located between the stroma and the aqueous humor - the clear fluid found in the front and rear chambers of the eye. The endothelium works as a pump, expelling excess water as it is absorbed into the stroma. Without this specialized function, the stroma could become water logged, hazy and opaque in appearance, also reducing vision.

The term "corneal disease" refers to a variety of conditions that affect mainly the cornea. These include infections, degenerations, and many other disorders of the cornea that may arise mostly as a result of heredity.