Conjunctivitis: Bacterial, Viral, Allergic and Other Types

All forms of conjunctivitis — including bacterial, viral, allergic and other types — involve inflammation of the transparent, mucous membrane (conjunctiva) covering the white part of the eye or sclera.

Although the conjunctiva is transparent, it contains most of the blood vessels on the eye's surface that are responsible for redness caused by inflammation.

Any stimulus that triggers eye inflammation will cause the conjunctival blood vessels to dilate. Against the background of the white sclera, these dilated blood vessels will make the eye look pink. Therefore, the term "pink eye" may be used to describe an inflamed eye associated with conjunctivitis.

Infectious causes of an inflamed eye and conjunctivitis include bacteria, viruses and fungi. Non-infectious causes include allergies, foreign bodies, chemicals and other sources. The term "pink eye" usually is reserved for highly contagious conjunctivitis caused by a virus (viral conjunctivitis).

Antibiotic eye ointments often effectively clear up bacterial conjunctivitis, but do not work for viral forms of the eye infection. Viral conjunctivitis typically resolves on its own within several days to a few weeks, just as a virus-caused cold or flu runs its course without treatment.

Coughing and sneezing can spread viral or bacterial forms of conjunctivitis, particularly among children who share close quarters in environments such as day care centers or schools. Certain pinkeye prevention measures such as frequent hand washing may be needed to keep infections from becoming widespread.

Bacterial conjunctivitis is a common type of pink eye, caused by bacteria that infect the eye through various sources of contamination. The bacteria can be spread through contact with an infected individual, exposure to contaminated surfaces or through other means such as sinus or ear infections.

The most common types of bacteria that cause bacterial conjunctivitis include Staphylococcus aureus, Haemophilus influenzae, Streptococcus pneumoniae and Pseudomonas aeruginosa. Bacterial conjunctivitis is usually associated with a thick discharge or pus and can affect one or both eyes.

As with any bacterial infection, antibiotics are required to eliminate the bacteria. Treatment of bacterial conjunctivitis is typically accomplished with topical antibiotic eye drops and/or eye ointments. The treatments are usually continued for one to two weeks, depending on the severity of the infection.

Viral conjunctivitis is another common type of pink eye and, as mentioned above, is considered the true "pink eye." Viral conjunctivitis is highly contagious, because airborne viruses can be spread through sneezing and coughing. Viral conjunctivitis also can accompany common viral upper respiratory infections such as measles, the flu or the common cold.

Viral conjunctivitis usually is associated with a watery discharge and ordinarily affects both eyes. Typically, however, the infection starts in one eye and quickly spreads to the other eye.

Unlike bacterial infections, antibiotics will not work against viruses. No eye drops or ointments are effective against the common viruses that cause viral conjunctivitis. But viral conjunctivitis is self-limited, which means it will go away by itself over a short period of time.

Typically with viral conjunctivitis, the third through the fifth days are the worst. After that, eyes begin to improve on their own. Treatment of viral conjunctivitis usually involves supportive therapies such as eye drops that help reduce the symptoms — for example, vasoconstrictors to whiten the eye, decongestants to reduce the surface swelling and/or antihistamines to reduce occasional itching. Treatments are usually continued for one to two weeks, depending on the severity of the infection.

Gonococcal and chlamydial conjunctivitis represent bacterial forms related to infections associated with sexually transmitted diseases including gonorrhea and chlamydia. Newborn babies may be exposed when they pass through the birth canal of an infected mother. Trachoma is a form of chlamydial infection, which causes the eye's surface to become scarred. Trachoma is the world's leading cause of preventable blindness.

Neonatal conjunctivitis found in newborn babies can cause blindness when left untreated. Up to 10 percent of all pregnant women in the United States have a sexually transmitted chlamydial infection. If these infections are untreated in mothers, the possibility that a newborn infant will develop a related eye infection ranges from 10 percent to 20 percent.*

Another type of sexually transmitted disease related to the herpes simplex virus type 2 found in the genital area can infect eyes of infants as they are being born. Herpes simplex virus type 1, commonly associated with cold sores on the mouth, also can cause a type of eye herpes resulting in pink eye.

If you are pregnant and suspect you may have a sexually transmitted disease, it is essential that you be checked and possibly treated for any infection prior to the birth of your baby.

In the United States, an antibiotic ointment often is applied as a basic standard of care for newborn infants, to help prevent the possibility of certain eye infections.

Allergic conjunctivitis can result when your eyes encounter a substance to which they are overly sensitive, such as pollen in the air.

Allergic conjunctivitis caused by eye allergies is very common. Eye allergies, like other types, can be triggered by allergens including pollen, animal dander and dust mites.

The most common symptom of allergic conjunctivitis is itchy eyes, which may be relieved with special eye drops containing antihistamines to control allergic reactions. These eye drops are available over-the-counter and in prescription forms.

Avoiding the allergen is also important in the treatment of allergic conjunctivitis. Allergic conjunctivitis can be seasonal or perennial (year-round) depending on the allergen causing the reaction.
 

Non-infectious conjunctivitis linked to eye irritation causing a pink eye can result from many sources including smoke, diesel exhaust, perfumes or certain chemicals. Some forms of conjunctivitis also can be related to sensitivities to certain ingested substances, including herbs such as eyebright and turmeric.**

Certain forms of pink eye, including giant papillary conjunctivitis (GPC), can be caused by the eye's immune responses, such as to wearing contact lenses or ocular prosthetics (artificial eyes). A reaction to preservatives in eye drops or ointments also can cause a toxic conjunctivitis.