Allergy: Allergic conjunctivitis, which effects both eyes, occurs in response to an allergy-causing substance like dust mites or pollen. This form is not contagious. The thin membrane that covers the eyelids and the exposed surface of the eyes is part of the immune system, and it can react to airborne allergens.
Typically, an allergic response is not triggered the first time the body encounters the allergen. The immune system may become sensitized the first time or several times after the body is exposed to an allergen. During this process, the body's white blood cells develop immunoglobulin E (IgE) antibodies to the allergens. Once sensitized, the antibodies quickly detect and bind to the allergens in the body. These antibodies also trigger the release of chemicals (like histamine) that cause allergic symptoms, including red, watery, itchy eyes.
Some cases of allergic conjunctivitis may be seasonal if they are caused by seasonal allergens, such as mold, pollen, and grass.
Cases that do not show seasonal variation are called perennial allergic conjunctivitis. This condition can occur at any time. It may be triggered by allergens like perfumes or protein deposits on the contact lenses.
Bacterial: An infection caused by bacteria like staphylococcus or streptococcus may cause conjunctivitis. Bacterial conjunctivitis is highly contagious. If the bacteria are present on the skin, it may spread to the eyes where it causes conjunctivitis. The bacteria can also be spread from sharing eye makeup or contact lenses or after touching or rubbing the eyes with dirty hands. This form is more common among children than adults.
A bacterial infection with chlamydia can also cause conjunctivitis. While this type of bacterial conjunctivitis is uncommon in the United States, it is prevalent in many Middle Eastern and African countries. Chlamydia is a sexually transmitted infection.
Viral: Viral infections are responsible for most cases of conjunctivitis. This type is highly contagious. Many of the viruses that cause the common cold can also lead to conjunctivitis. The adenovirus, which is prevalent during the rainy season or winter months, may also cause viral conjunctivitis.
Chemicals and irritants: Conjunctivitis may also be caused by exposure to certain chemicals and irritants. For instance, irritant gases like chlorine or hydrochloric acid, natural toxins like ricin, or splash injuries from chemicals may lead to conjunctivitis. This type of conjunctivitis is not contagious.
Other: Other causes of conjunctivitis include ultraviolet burns, overuse of contact lenses, foreign objects, vitamin deficiency, exposure to chickens infected with Newcastle disease, pre-cancerous cells, and some conditions of unknown cause like sarcoidosis (disease that causes lesions to develop in the lungs, liver, spleen, skin, eyes, and lymph nodes). None of these types of conjunctivitis are contagious.
General: Conjunctivitis symptoms and signs are generally nonspecific. Redness, irritated and watery, itchy eyes, blurred vision, and discharge that forms a crust during sleep are common symptoms of conjunctivitis. Other less common symptoms may include pain and sensitivity to light.
Allergic: Allergic conjunctivitis affects both eyes. The eyes become extremely itchy and the eyelids swell. This form causes edema (swelling caused by excess water in the tissues) of the conjunctiva and sometimes the whole eyelid. The eyes may also secrete a mucus discharge.
Bacterial: Bacterial conjunctivitis usually affects one eye at first and often spreads to the other. Common symptoms include a feeling of grittiness in the eyes, irritation, reddening of the eyes and a thick yellow-green discharge that may cause the lids to stick together, especially after sleeping. This condition may be associated with a sore throat or lung infection (like pneumonia).
Viral: Viral conjunctivitis usually starts with one eye and often spreads to the other. Viral conjunctivitis is usually associated with upper respiratory (lung) infection, a common cold, or sore throat. Common symptoms include watery eye discharge and itchy eyes.
Chemicals and irritants:
Irritant or toxic conjunctivitis is usually painful and it may cause reddening of the eyes. The eyes may secrete mucus.
General: Although tests are available to diagnose the specific cause of conjunctivitis, a diagnosis is typically made after a physical examination and medical history. A slit lamp exam can confirm a diagnosis. A sample of the patient's eye discharge may be cultured to determine whether a bacteria or virus is the cause. A skin test or antigen-specific immunoglobulin (IgE) test may be performed to determine whether the patient is allergic to specific substances.
Slit lamp exam: The slit lamp is a microscope with a light that helps the eye doctor observe the eye under high magnification. The doctor is able to see the front and the back of the eye.
Culture: A sample of the patient's eye discharge may be cultured. When a bacterial or viral infection is suspected, the sample is placed on a Petri dish and allowed to grow in a laboratory. If a bacteria or virus is causing conjunctivitis, it will grow on the Petri dish.
Skin test: A skin test is used to determine whether a patient is allergic to certain substances. During the test, the skin is exposed to different allergens. The skin is then observed for an allergic reaction. If an allergen triggers an allergic reaction to a test, the patient will develop reddening, swelling, or a raised, itchy red wheal (bump) that looks similar to a mosquito bite. The healthcare provider will measure the size of the wheal and record the results. The larger the wheal, the more severe the allergy. A skin test is typically conducted in a healthcare provider's office. Skin tests cause minimal, if any, discomfort. The needles used barely penetrate the skin's surface and will not cause bleeding.
Allergen-specific immunoglobulin (IgE) test: An allergen-specific immunoglobulin E (IgE) test, commonly referred to as radioallergosorbent test (RAST®), may also be used to determine whether the patient is allergic to specific substances. However, this test is less accurate than a skin test. It is usually performed in patients who have coexisting severe skin diseases (like eczema or psoriasis) that make it difficult to interpret a skin test.
The in vitro test is conducted in a laboratory. During the procedure, a sample of blood is taken from the patient. The blood is then sent to a laboratory that performs specific IgE blood tests. The allergen is bound to an allergosorbent (paper disk). Then the patient's blood is added. If the blood contains antibodies (immunoglobulins that detect and bind to antigens) to the allergen, the blood will bind to the allergen on the disc. A radiolabelled ANTI-IgE antibody is then added to the disc to measure the level of immunoglobulin E present in the blood. The higher the radioactivity, the higher the level of IgE in the blood and the more severe the allergy.
A qualified healthcare provider will interpret the results of the test. In general, the sensitivity of these tests range from 50-90%, with the average being about 70-75%. The patient will receive test results in about seven to 14 days.