Allergic conjunctivitis is inflammation of the conjunctiva caused by an allergic reaction.
The conjunctiva (the membrane that lines the eyelid and covers the white of the eye) contains a large number of cells from the immune system (mast cells) that release chemical substances (mediators) in response to a variety of stimuli (such as pollens or dust mites). These mediators cause inflammation in the eyes, which may be brief or long-lasting. About 20% of people have some degree of allergic conjunctivitis.
Seasonal allergic conjunctivitis and perennial allergic conjunctivitis are the most common types of allergic reaction in the eyes. Seasonal allergic conjunctivitis is often caused by mold spores or tree, weed, or grass pollens, leading to its typical appearance in the spring and early summer. Weed pollens are responsible for symptoms of allergic conjunctivitis in the summer and early fall. Perennial allergic conjunctivitis occurs year-round and is most often caused by dust mites, animal dander, and feathers.
Vernal keratoconjunctivitis is a more serious form of allergic conjunctivitis in which the stimulant (allergen) is not known. The condition is most common among boys, particularly those aged 5 to 20 years who also have eczema, asthma, or seasonal allergies. Vernal keratoconjunctivitis typically reappears each spring and subsides in the fall and winter. Many children outgrow the condition by early adulthood.
People with all forms of allergic conjunctivitis develop intense itching and burning in both eyes. Although usually equal, occasionally one eye may be more affected than the other. The conjunctiva becomes red and sometimes swells, giving the surface of the eyeball a puffy appearance that many people find disturbing. With seasonal and perennial conjunctivitis, there is a large amount of thin, watery discharge. At times the discharge is stringy. Vision is seldom affected. Many people have a runny nose.
With vernal keratoconjunctivitis, the eye discharge is thick and mucuslike. Unlike other types of allergic conjunctivitis, vernal keratoconjunctivitis often affects the cornea (the clear layer in front of the iris and pupil), and painful ulcers develop. These ulcers cause deep eye pain with exposure to bright light and sometimes lead to a permanent decrease in vision.
Diagnosis and Treatment
Doctors recognize allergic conjunctivitis by its typical appearance and symptoms. The condition is treated with anti-allergy eye drops. Tear supplements can help reduce symptoms. Drops that have an antihistamine, such as ketotifen, may be enough for mild cases. This drug can be bought without a prescription. If ketotifen is ineffective, prescription antihistamine eye drops such as olopatadine, or mast cell stabilizers such as azelastine may be effective. Nonsteroidal anti-inflammatory eye drops, such as ketorolac, help relieve symptoms. Corticosteroid eye drops have more potent anti-inflammatory effects; however, they should not be used for more than a few weeks without close monitoring because they may cause increased pressure in the eyes (glaucoma), cataracts, and an increased risk of eye infections.
Last full review/revision November 2012 by Melvin I. Roat, MD, FACS