Infectious conjunctivitis is inflammation of the conjunctiva usually caused by viruses or bacteria.
A variety of microorganisms may infect the conjunctiva (the membrane that lines the eyelid and covers the white of the eye). The most common organisms are viral, particularly those from the group known as adenoviruses. Bacterial infections are less frequent. Both viral and bacterial conjunctivitis are quite contagious, easily passing from one person to another, or from a person's infected eye to the uninfected eye.
Some viruses that cause bodywide symptoms also cause red, irritated eyes. Such viral infections include measles, mumps, rubella, chickenpox, Zika, and some of the viruses that cause cold- and flu-like symptoms.
Fungal infections are rare and occur mainly in people who use corticosteroid eye drops for a long time or have eye injuries involving organic matter, such as plants or dirt.
Newborns are particularly susceptible to eye infections caused by Chlamydia trachomatis or Neisseria gonorrhoeae, which they acquire from organisms in the mother's birth canal (conjunctivitis of the newborn—see Table: Some Infections of Newborns).
Inclusion conjunctivitis is a particularly long-lasting form of conjunctivitis caused by certain strains of the bacterium Chlamydia trachomatis. Inclusion conjunctivitis usually spreads by contact with genital secretions from a person who has a genital chlamydial infection. Trachoma is another type of conjunctivitis caused by Chlamydia trachomatis.
Gonococcal conjunctivitis is another type of conjunctivitis and is caused by Neisseria gonorrhoeae(gonorrhea), a sexually transmitted disease that also may spread to the eye by contact with genital secretions from a person who has a gonorrheal infection.
Severe infections may scar the conjunctiva, causing abnormalities in the tear film. Sometimes, severe conjunctival infections spread to the cornea (the clear layer in front of the iris and pupil).
When infected, the conjunctiva becomes pink from dilated blood vessels, and a discharge appears in the eye. Often the discharge causes the person's eyes to stick shut, particularly overnight. This discharge may also cause the vision to blur. Vision improves when the discharge is blinked away. If the cornea is infected, vision also blurs but does not improve with blinking. Sometimes the eye feels irritated, and bright light may cause discomfort. Very rarely, severe infections that have scarred the conjunctiva lead to long-term vision difficulties.
Viral conjunctivitis differs from bacterial conjunctivitis in the following ways:
Eye discharge tends to be watery in viral conjunctivitis and thicker white or yellow in bacterial conjunctivitis.
An upper respiratory infection increases the likelihood of a viral cause.
A lymph node in front of the ear may be swollen and painful in viral conjunctivitis but is usually not in bacterial conjunctivitis.
These factors, however, cannot always accurately differentiate viral conjunctivitis from bacterial conjunctivitis.
People with inclusion conjunctivitis or with conjunctivitis caused by gonorrhea often have symptoms of a genital infection, such as discharge from the penis or vagina and burning during urination.
Conjunctivitis in the newborn causes inflammation of the eyelid and a discharge of pus.
Doctors diagnose infectious conjunctivitis by its symptoms and appearance. The eye is usually closely examined with a slit lamp (an instrument that enables a doctor to examine the eye under high magnification). Samples of infected secretions may be sent to a laboratory to identify the infecting organism by a culture. However, doctors usually send samples to a laboratory only in certain situations:
When the symptoms are severe or recurring
When Chlamydia trachomatis or Neisseria gonorrhea is thought to be the cause
When the person has an immune system defect (such as human immunodeficiency virus [HIV]/AIDS)
When the person has had an eye problem, such as a corneal transplant or eye bulging caused by Graves disease
Most people with infectious conjunctivitis eventually get better without treatment. However, some infections, particularly those caused by some bacteria, may last a long time if not treated.
Inclusion conjunctivitis may persist for months if not treated.
Conjunctivitis in the newborn may cause blindness if not treated.
If discharge accumulates on the eyelid, people should gently wash the eyelid (with the eye closed) with tap water and a clean washcloth. Warm or cool compresses sometimes soothe the feeling of irritation. Because infectious (bacterial or viral) conjunctivitis is highly contagious, people should use hand sanitizers before and after cleaning the eye or applying drugs to the eye. Also, a person should be careful not to touch the infected eye and then touch the other eye. Towels and washcloths used to clean the eye should be kept separate from other towels and washcloths.
People with infectious conjunctivitis generally stay home from work or school for a few days, just as they would with a cold. In the most severe cases of viral conjunctivitis, people sometimes stay home for weeks.
Antibiotics are helpful only in bacterial conjunctivitis. However, because it is difficult to distinguish between bacterial and viral infections, doctors sometimes prescribe antibiotics for everyone with conjunctivitis. Antibiotic eye drops or ointments, such as moxifloxacin, ciprofloxacin, or trimethoprim/polymyxin, which are effective against many types of bacteria, are used for 7 to 10 days. Drops are usually effective, but ointments are sometimes used because they last longer if the eye is watering a lot. However, some people may not want to use ointments because they can blur vision for up to 20 minutes after they are applied.
Inclusion conjunctivitis requires antibiotics, such as azithromycin, doxycycline, or erythromycin, which are taken by mouth.
Gonococcal conjunctivitis may be treated with a single injection of ceftriaxone and a single dose of azithromycin taken by mouth.
Conjunctivitis of the newborn is prevented by routinely giving silver nitrate eye drops or erythromycin ointment to all infants at birth. If an infection develops despite these treatments, newborns are given drugs depending on which bacterium is causing the infection. Infections caused by Neisseria gonorrhoeae are treated with ceftriaxone given by vein (intravenously) or injected into a muscle. Infections caused by Chlamydia trachomatis are treated with erythromycin. The parents should also be treated.
Most people with viral conjunctivitis get better in a week or two and do not need any specific treatment. However, corticosteroid eye drops may be needed in some people with severe adenoviral conjunctivitis (see What Is Pinkeye?), particularly in those in whom blurring and sensitivity to light are interfering with important daily activities.
Antiviral eye drops are not helpful for conjunctivitis caused by viruses (antiviral eye drops are used for some cornea infections caused by viruses—see Herpes Simplex Keratitis).