Causes
Infectious conjunctivitis is the most common cause of pinkeye around the
world. Causes of infectious conjunctivitis are numerous and can usually
be classified as viral, bacterial, or fungal.
Some of the most common causes of serious eye infection include:
Ocular histoplasmosis syndrome (OHS): Histoplasmosis is a fungal infection
of the lungs, which is caught by inhaling spores. It's common in river valleys
around the world. In the U.S., it is concentrated
in the area known as the Bible Belt (called the Histo Belt by eye doctors).
Over 90% of adults in the southeastern U.S. have had histoplasmosis, which usually
causes no symptoms. In a small fraction of cases, the fungus migrates to the
retina many years or decades later. Once there, it damages the retina, particularly
the macula, the vital center part where the vision cells are most concentrated.
It causes symptoms and retinal decay very similar to macular degeneration, and
can destroy the central part of the field of vision. People of African descent
are largely immune. Although only a tiny minority of people with histoplasmosis
go on to suffer OHS, the fungus is so common that OHS is the leading infectious
cause of legal blindness in Americans between the ages of 20 to 40 years.
Chlamydia and gonorrhea: These extremely common sexually transmitted
diseases (STDs) are leading causes of visual damage in adults, though they rarely
produce total blindness. The infection gets into the eye either directly through
genital fluids such as semen, or when infected people rub their eyes after handling
infected genital areas. Babies born to genitally infected women are at especially
high risk of eye infection. Neisseria gonorrheae is one of the few bacteria
capable of penetrating the protective layers of the eye, causing inner-eye infection.
Herpes simplex: This widely prevalent STD can be caught as a skin
disease (cold sores). Herpes viruses can infect the eye in the same way as chlamydia
or gonorrhea. Like these diseases, herpes can cause pitting and ulceration of
the cornea. Chronic herpes infection can cause acute retinal necrosis
(ARN), particularly in men. This is a major destruction of retinal tissue, and
causes dramatic damage to vision. About 15% of people with chronic ocular herpes
simplex lose some vision.
Shingles (herpes zoster, varicella zoster): Shingles
are a chronic recurrence of the infection that initially causes chickenpox.
The sores known as shingles are infectious and can cause chickenpox in others.
They can also cause ocular infection if you touch the eyes after touching a
sore. While herpes simplex is the leading cause of acute retinal necrosis
in the young, varicella zoster is the leading cause in people over 50
years of age because shingles is more common in this age group.
Bacterial keratitis: This is an infection of the cornea by common bacteria.
Normally, these bacteria can't penetrate the outer layer of the eye, and cause
only conjunctivitis. However, eye injury, lack of oxygen due to contact lenses,
or a weak immune system can all facilitate entry into the cornea, the clear
layer in the front of the eye. Fungi can cause fungal keratitis under similar
circumstances.
Infections that can cause conjunctivitis or keratitis (inflammation of the cornea)
include:
- the STDs syphilis, gonorrhea, chlamydia, herpes simplex, and hepatitis B
- tuberculosis
- leprosy
- Lyme disease
- acanthamoeba - a common parasite
- crab lice - these tiny animals can live and breed in your eyelashes and
are invisible to the naked eye
- Epstein-Barr or infectious mononucleosis
- mumps, measles, influenza, or shingles
- onchocerciasis (river blindness)
- sarcoidosis - not proven to be an infectious disease, but almost certainly
is
- mycosis (general name for fungal infections) - candida, the fungus that
causes thrush, is one of more than 60 types of fungus that can infect the
eye
Infections that can damage the retina and the inner eye include:
- syphilis
- tuberculosis
- toxoplasmosis
- sarcoidosis
- herpes simplex
- varicella zoster (shingles and chickenpox)
- gonorrhea
- histoplasmosis
- cytomegalovirus, which doesn't affect healthy people but is the leading
cause of blindness in people with AIDS