How To Treat Corneal Abrasions

The cornea is truly the eye's window. It's the transparent, domed "watch glass" that sits over the sclera (the "white" of the eye). Through this clear porthole the iris and pupil are easily visible; looking further still beyond them, we can see all the way to the back of the eye - the vitreous, retina, and optic nerve.

The wafer-thin cornea (amazingly, only about 1 millimeter thick) is like a cake with five layers, each with its own special function. On top are epithelial (outer lining) cells; this vital layer (also called the epithelium) protects the rest of the cornea and provides a smooth surface for tears.

Next comes the cellophane-thin Bowman's membrane; then the tough, transparent stroma, the bulk of the cornea (the cake itself); then another layer of cellophane, called Descemet's membrane. These middle three layers act as scaffolding, providing structural support to the cornea as it arches over the front of the eye. Last is the single layer of endothelial (inner lining) cells (also called the endothelium). Because this important layer touches the aqueous of the eye's anterior chamber, it serves as a sort of "bilge pump," keeping the cornea free of excess moisture. When this pump malfunctions, the cornea can swell, and this can distort or even damage vision.

The cornea normally does not contain any blood vessels. However, it is rich in sensory nerve fibers: under the epithelial layer alone are about seventy of them, which helps explain why the cornea is so sensitive to pain. The epithelial cells act as a protective blanket, like enamel on a tooth, insulating the nerve fibers from the world. When that blanket is frayed - or, continuing the tooth analogy, when the enamel is cracked or has a cavity - those ultra sensitive nerves react painfully. Even a small loss of epithelial cells can be excruciating, if it exposes these nerve endings.

Corneal Abrasions

Because of the abundance of nerves throughout its layers, even a slight injury or irritation to the cornea can result in a lot of discomfort or pain. An abrasion - a scrape of the epithelium, or outer surface - is the most common injury to the cornea. It can happen so easily - when the eye gets too close to a baby's fingernail, for instance, or the corner of an envelope, or a tree branch. All of a sudden it feels as if there's a hot poker in your eye.

Other symptoms include redness, a feeling like there's a piece of grit in your eye, and extra sensitivity to bright lights. Because it's often difficult to see the actual injury with the naked eye, eye doctors rely on special fluorescent dyes, which target and highlight areas of damage, to help us determine the extent of the wound. Fortunately, despite the severe discomfort and blurred vision that often accompany corneal abrasions, these injuries usually heal fairly quickly, sometimes in a matter of hours, sometimes within a few days - and don't leave any lasting damage.

For treatment, basically, the cornea must heal itself, and all we can do is provide the best conditions possible. (Think of skin injured by a scrape or burn; it hurts until your skin lays down new layers of cells, which insulate the nerves beneath.) Thus, the main treatment for a corneal abrasion is simply to patch the eye. It's not quite as easy as it sounds - in other words, you shouldn't try to do it yourself with an eye patch from the drugstore - because to be effective, the eye patch must immobilize the eyelid and prevent it from rubbing over the injured area. The epithelial cells need time to multiply and coat the injury, which means that the patch needs to be tight enough to keep the eyelid still. It takes several eye patches - generally three - to create enough bulk to secure the lid. (Eye doctors either stack three patches over the eyelid or use two, with the one directly on the eyelid folded in half.)

The eye pads are fixed over the eyelid with at least four pieces of surgical tape, extending from the forehead to the cheek. Sometimes, when eye patches can't be tolerated or when the abrasion doesn't appear to be healing, eye doctors apply a special "bandage" contact lens over the abrasion. Bandage contact lenses allow the patient to avoid having to cope with the nuisance of wearing a large and bulky eye patch and enables the abraded eye to see while it heals.