Eye Allergy (cont.)

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What is the basic anatomy of the outer eye?

Eye allergies mainly involve the conjunctiva, which is the tissue lining (mucus membrane) that covers the white surface of the eyeball and the inner folds of the eyelids. The conjunctiva is a barrier structure that is exposed to the environment and the many different allergens (substances that stimulate an allergic response) that become airborne. It is rich in blood vessels and contains more mast cells (cells that release histamine, a chemical mediator of allergic reactions) than the lungs.

The lacrimal (tear) glands are located in the upper and outer portions of the eye. They are responsible for producing the watery component of tears, which keeps the eye moist and washes away irritants. The tears also contain important components of the immune defense such as immunoglobulins (antibodies), lymphocytes (specialized white blood cells), and enzymes.

The cornea is the transparent sheath in front of the lens of the eye. The cornea has no blood vessels and very little immune activity.

Why are the eyes an easy target for allergies?

When you open your eyes, the conjunctiva becomes directly exposed to the environment without the help of a filtering system such as the cilia, the hairs commonly found in the nose.

Allergy fact

Approximately 54 million people, about 20% of the U.S. population, have symptoms of allergies. Almost half of these people have allergic eye disease.

People who are more susceptible to allergic eye disease are those with a history of allergic rhinitis and atopic dermatitis and those with a strong family and/or personal history of allergy. Symptoms usually appear before the age of 30.

The scenario for developing allergy symptoms is much the same for the eyes as that for the nose. Allergens cause the allergy antibody IgE to coat numerous mast cells in the conjunctiva. Upon reexposure to the allergen, the mast cell is prompted to release histamine and other mediators. The result is itching, burning, and runny eyes that become red and irritated due to inflammation, which results in congestion. The eyelids may swell, even to the point of closing altogether. Sometimes, the conjunctiva swells with fluid and protrudes from the surface of the eye, resembling a "hive" on the eye. These reactions may also induce light sensitivity. Typically, both eyes are affected by an allergic reaction. Occasionally, only one eye is involved, particularly when only one eye is rubbed with an allergen, as this causes mast cells to release more histamine.

Medically Reviewed by a Doctor on 4/11/2014

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Eye Allergy - Treatments Question: What treatment do you use for your eye allergies or allergic eye disease?
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