What is conjunctivitis (pink eye)?

Conjunctivitis is an inflammation of the conjunctiva, which is a thin, transparent membrane that covers the surface of the inner eyelid and the front of the eye. This membrane reacts to a wide range of bacteria, viruses, allergy-provoking agents, irritants and toxic agents, as well as to underlying diseases within the body. The conjunctiva is usually clear, but if irritation or infection occurs, the lining becomes red and swollen.

The common name for conjunctivitis is "pink eye". Pink eye is very common, usually not serious, and often resolves in a few days without medical treatment.

The main types of conjunctivitis are infectious and allergic.

Neonatal conjunctivitis occurs in a newborn child. One of the most common causes is sexually transmitted diseases such as Chlamydia, which are acquired by the baby as it is born. This needs to be treated with antibiotics and the mother and partner will also need treatment.

• Infectious conjunctivitis is usually caused by a contagious virus or bacteria (but may occasionally be caused by a fungus or other organism).

• "Pink eye" refers to any kind of conjunctivitis. However, especially in schools, "pink eye" refers to a particular viral conjunctivitis (caused by the adenovirus) that is very contagious. Occasionally this form of pink eye can be associated with infection of the cornea (the clear portion of the front of the eyeball).

• Other viruses, such as those causing herpes simplex, chicken pox, shingles, or measles, can also infect the conjunctiva.

• Blepharitis is inflammation and infection of the eyelids, usually marked by redness and crusting at the margins along the lash line. This can cause a secondary bacterial conjunctivitis. Other problems with the eyelids that can lead to or exacerbate conjunctival irritation are styes, a lump called a chalazion, or tear deficiency.

• A raised, yellowish growth on the wall of the eye called a pingueculum can often become inflamed by exposure to irritating environments, such as a dry, windy climate.

• Allergies to pollen, cosmetics, animals or fabrics often bring on allergic conjunctivitis.

• Chemical pink eye can result when any irritating substance enters the eyes. Common irritants are household cleaners, sprays, smoke, smog, industrial pollutants and chlorine in swimming pools.

• Conjunctivitis may be drug-induced. Reactions can occur to preservatives in eye drops, or after prolonged use of topical antibiotics or antivirals.

• Conjunctivitis is a well-known complication of wearing contact lenses.

Mimicking disorders
• Uncommon underlying illnesses can cause redness of the eye, mimicking conjunctivitis. Most often these are rheumatic diseases, such as rheumatoid arthritis and certain inflammatory bowel diseases.

• Subconjunctival haemorrhage, or "eye bruise", occurs when a portion of the wall of the eye (white of the eye) suddenly becomes bright red. This occurs when the tiny blood vessels covering the whites of the eyes rupture from trauma or changes in pressure within the head (for example, as a result of forceful laughing, coughing, sneezing or vomiting, diving under water, or even bending upside down). This tends to be asymptomatic and is usually pointed out by another person. It can appear quite alarming, but is in fact a harmless haemorrhage or bruise under the conjunctiva.

• The wall of the eye beneath the conjunctiva can become inflamed (episcleritis or scleritis). These conditions often involve only one eye. They are generally not infectious processes, and sometimes are associated with various medical conditions. They are potentially serious and need to be evaluated by an ophthalmologist and usually treated with anti-inflammatory medications.

• Acute glaucoma (raised pressure within the eye) can cause a red eye.

• Foreign bodies, scrapes and sores on the cornea can cause a red eye.