Conjunctivitis is the term used by medical eye doctors (ophthalmologists) to describe inflammation of the conjunctiva, In ordinary terms, conjunctivitis is simply the most common cause of red or "pink" eye. The white of the eye (sclera) is covered by a thin, filmy membrane called the conjunctiva which produces mucus to coat and lubricate the surface of the eye. It normally has fine blood vessels within it, which can be seen on close inspection. When the conjunctiva becomes irritated or inflamed, the blood vessels which supply it enlarge and become much more prominent, and the eye turns red.

Many different sources of eye irritation can cause conjunctivitis.

The most common are

· infections,

· allergies, and

· environmental irritants.

Because the conjunctiva is a simple tissue, it responds to all these stimuli in one way; it turns red.

Infectious causes of conjunctivitis include bacteria and viruses. Bacterial infections, such as staphylococcus or streptococcus, cause a red eye which is associated with considerable amounts of pus. If the amount of discharge from the eye is great, an acute infection is likely, and prompt consultation with an ophthalmologist is advisable.

On the other hand, some bacterial infections are more chronic and may produce little or no discharge except for some mild crusting of the eyelashes in the morning.

Viruses are also common causes of conjunctivitis. Some viruses produce the familiar red eyes, sore throat, and runny nose of a common cold. Others may infect only one eye. Viral conjunctivitis usually produces a watery discharge and lasts from one to two weeks.

Infectious conjunctivitis, whether bacterial or viral, can be quite contagious, so contact with the patient’s tears through used handkerchiefs and towels should be avoided. Hand washing after contact with the patient helps to prevent spread of the infection.

Allergies tend to cause a type of conjunctivitis which produces a discharge. Some kinds of allergies, like hay fever, make the eyes very itchy, while others may merely produce a chronic redness. Finally, environmental irritants such as smoke or fumes may cause conjunctivitis. Any type of conjunctivitis is aggravated by dryness of the eyes.

There are several eye diseases which also produce a red eye and which can lead to blindness unless recognized and treated. It is important to avoid confusing them with conjunctivitis, so a medical evaluation of a red eye, by an ophthalmologist, is always a good idea. This is especially important if pain, blurred vision, or severe light sensitivity are present, since these symptoms are not typically found in simple conjunctivitis. Pain, blurred vision, or severe light sensitivity may signal the presence of glaucoma, an ulcer of the eye, or an inflammation of the inside of the eye.