Now that school is back is session and child day care services are in full swing, the incidence of "pink eye" is starting to pick up. This is a very common condition that accounts for over 30 percent of patient visits for eye problems.

Conjunctivitis is the medical term for "pink eye." The conjunctiva is the continuous connective tissue membrane that covers the inside of the eyelids. It then folds back on itself to cover the front of the eyeball up to the edge of the cornea (where the white part of the eye meets the iris or colored part of the eye).

The purpose of the conjunctiva is to provide a barrier to keep infectious organisms from entering the eye tissue itself. Conjunctivitis results when there is an irritation or breakdown of this defensive layer, a change in the normal organisms inhabiting the eye, or trauma that breaches the membrane.

There are a number of causes of conjunctivitis. The most common are bacteria, viruses, allergies, fungi, parasites, and chemicals. These irritants cause varying degrees of redness, discharge, irritation and perhaps even pain on exposure to bright light, known as photophobia.

It can be difficult to tell the exact cause of conjunctivitis unless the doctor has special equipment. Ophthalmologists and optometrists have slit lamps (the instrument that you rest your chin on where the doctor sweeps a bright light across your eye) that can help differentiate the cause.

Doctors without special equipment can sometimes get clues to the cause of the inflammation. For instance, people who have had a recent cold are more likely to be suffering from a viral conjunctivitis. Viruses are also more common from early spring through late fall. Bacterial conjunctivitis is more common in the winter and spring. Patients usually recall exposures to things that might cause chemical or allergic conjunctivitis.

The symptoms of conjunctivitis can be quite variable. Most causes result in some type of eye discharge that results in matting of the eyes, particularly in the mornings when the eyelids may be stuck together. Patients may describe cloudy vision and itching, burning or a "sand in the eyes" sensation.

Bacterial conjunctivitis usually comes on fairly rapidly, has minimal pain and may have some associated itching. There is often thick discharge that may be yellow or green. Staph and Strep are the usual causative organisms. More serious bacterial organisms include Chlamydia and Neisseria gonorrhoeae, the organism responsible for gonorrhea. These latter two bacteria can lead to severe scarring and blindness, particularly in infants.

Viral conjunctivitis typically starts more slowly than bacterial types and does not have much associated pain. The discharge is generally waterier and does not have as much matting. It usually lasts a week or longer and is transmitted like the common cold - through sneezing, coughing, touching infected surfaces and also through contact with contaminated swimming pools.

Adenoviruses are the most common cause of viral conjunctivitis. Herpes viruses, like varicella virus associated with shingles, can cause very serious eye infections. These viruses can infect the surface of the cornea and cause scarring and loss of vision.

Allergic conjunctivitis is also very common. The hallmark of this type of irritation is itching along with watery discharge and burning. There is often associated sneezing. There is usually a history of exposure to some known allergen.

Treatment for conjunctivitis is based on the cause. Most cases will resolve on their own with time without any lasting effects. Most people don't want to wait it out.

Since it is often difficult to tell whether the infectious agent is bacterial or viral, most doctors will choose to treat a presumed infection with antibiotic eye drops or ointment. Drops are nice since they don't interfere with vision. Ointments are more soothing and allow the medication to be in contact with the conjunctiva longer, but can temporarily cloud vision.

Local treatment with cool compresses can also be soothing. Most schools and daycares want children to be treated for at least 24 hours before they return.

Allergic conjunctivitis can be an ongoing problem as long as the offending agent is in the air. The person should avoid the allergen if possible. In addition to cool compresses, over the counter antihistamine eye drops such as Naphcon A can also be helpful.

There are steps you can take to help prevent conjunctivitis. Wash your hands frequently. You can also use hand sanitizer, but it is not as effective. Also, don't share eye drops or washcloths with people who have colds or eye infections.

Dr. John Roberts is a local physician. His column appears in Monday's edition of the Times, and he has a daily health tip on the front page. Dr. Roberts is one of the owners of Sagamore News Media, parent company of The Times.