Inflammation in the body is an immune response to tissue injury. Swelling of the injured tissue occurs, resulting in pain, heat, and redness as the affected area tries to repair itself. Any type of tissue can become inflamed, including the conjunctiva (tissue that lines the eyelid). Conjunctivitis has a number of potential causes, some of which are infectious and include bacteria, protozoans, fungi and viruses.
Most Common Causes of Infectious Conjunctivitis
Viruses are the most common cause of conjunctivitis, and the term “pink eye” typically refers to a viral infection of the conjunctiva. Adenoviruses, a group of viruses that cause the common cold, can invade the conjunctiva, resulting in pink eye. Some herpes viruses can also cause pink eye infection.
Bacteria that most often result in conjunctivitis include the Gram negative Haemophilus influenzae and Chlamydia trachomatis, one of the leading causes of non-traumatic blindness worldwide; blindness that occurs as a result of conjunctiva inflammation so severe that the eyelashes turn inward, scratching and scarring the cornea. The Gram-negative species that causes gonorrhea, Neisseria gonorrhoeae, can also infect the conjunctiva.Gram-positive bacteria associated with conjunctivitis include Staphylococci, Streptococci. Protozans, such as Acanthamoeba and Naegleria can cause conjunctivitis as well.
Conjunctivitis caused by microbes is very contagious. Frequent hand washing, and treatment can help resolve and prevent the spread of infection. However, inflammation of the conjunctiva is not only caused by infection. Allergies, certain chemical irritants, and some contact lenses, especially extended wear, can also irritate the conjunctiva.
Treatment of Pink Eye
The body has its own methods of protecting the conjunctiva. Blinking and tears help remove debris that could irritate the eye and also help wash away bacteria. Additionally, the fluid bathing the eyes contains enzymes and antibodies that naturally kill bacteria.
Treatment of infectious conjunctivitis depends on the cause. Viral conjunctivitis does not have a treatment that will eliminate the virus. Antibiotic eye drops, ointments or pills may be prescribed to treat bacterial conjunctivitis, and may also be used in cases of viral conjunctivitis, as a preventative to bacterial infection.
Conjunctivitis caused by allergies may resolve with allergy treatment, or disappear on its own when the allergen causing the inflammation is no longer present in the environment (such as with seasonal allergies).
The discomfort of conjunctivitis can be eased by applying a clean cloth soaked in warm water to closed eyes.
For more information on microbiology, see the Virtual Microbiology Classroom of the science education website Science Prof Online.
Sources
Bauman, R. (2012) “Microbiology with Diseases by Body System,” Benjamin Cummings.
National Center for Biotechnology Information, U.S. National Library of Medicine, (2011) “Conjunctivitis: Inflammation - conjunctiva; Pink Eye,” A.D.A.M. Medical Encyclopedia.
Medscape Reference (2011) Bacterial meningitis: Overview.
WebMD (2009) Pink Eye: Overview. Healthwise, Inc.
Tami Port - Tami Port is a college professor of cell and microbiology and creator of ScienceProfOnline.com, a free science education website.
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