In February, 2002, the Dartmouth College student health center experienced a sudden influx of students coming in for treatment of acute eye discomfort--red and itchy eyes and lashes crusty with dried material that had exuded from their eyes overnight. Many of these students had a roommate, friend, or sports teammate with similar symptoms. Over the next two months an epidemic of the disorder sped through the entire student body. Before it was over it had affected 22% of the freshman class and 20% of the sophomores, with somewhat lower rates for juniors and seniors. This incident provides an excellent demonstration of just how infectious is the malady these students had--conjunctivitis, also known as "pink eye."
What is conjunctivitis?
The suffix "itis" simply means inflammation of whatever organ or body part to which it is attached; thus conjunctivitis is an inflammation of the thin membrane covering the eye called the conjunctiva. The conjunctiva lines the inner part of the eye lids, from the front edge at the lashes around to the eye ball itself, and continues out over the white part of the eye, or sclera. Normally you cannot see the conjunctiva because it is transparent. This is why the sclera of the normal eye looks white; you are seeing it through the transparent conjunctiva. If you pull down your lower eye lid you will again be looking through the conjunctiva and seeing the normal reddish color of the tissues beneath this thin membrane.
When a person gets conjunctivitis, however, the conjunctiva becomes very obvious; the inflammation turns it thick and red and causes it to weep fluid. This fluid can be almost clear, like tears, or more cloudy. It can even be yellow or green and thick as pus. Dried fluid on the lashes gives the characteristic crusty appearance of a conjunctivitis patient's eyes. This may be so substantial the person's eyes are virtually glued shut upon awakening in the morning.
The figure above shows what a moderately severe case of conjunctivitis looks like. This person's entire sclera is reddened by the inflammation and it is easy to see how thick and boggy is the normally pristine and clear conjunctiva. If you were to pull back this person's lids you would also see inflamed tissues in the crevices above and below the eye. Milder cases of conjunctivitis, as illustrated in the figure below, may show only red, bloodshot eyes.
Besides the typical symptoms of itching, burning eyes with clear or cloudy discharge, it is common for the person to have a foreign body sensation, the feeling that something is in the eye. Severe pain is uncommon; if this is present it suggests there may be a true foreign body stuck in the eye or else injury to the cornea, the surface of the central portion of the eye. Conjunctivitis does not generally affect vision. However, if the inflammation is severe, the person may have some difficulty seeing clearly because the discharge may cloud vision. Conjunctivitis is a common illness, and anyone can get it.
What causes conjunctivitis?
The conjunctiva can become inflamed from three common causes: environmental irritants, allergies, or infections. The first of these is usually easy to diagnose because the person experiences red and itchy eyes when exposed to an irritant such as tobacco smoke or swimming pool chlorine. Allergic conjunctivitis is common in anyone with allergies, such as to pollen or cats; the red, burning eyes reproducibly follow exposure to those specific things or come at predictable seasons of the year. When we speak of pink eye, however, we are generally referring to a third cause for conjunctivitis--infections. This is what the Dartmouth students were contracting from one another.
Two principal kinds of infectious agents cause conjunctivitis: bacteria and viruses. Medical authorities vary in assigning relative frequencies to these two categories, but overall roughly half of cases are caused by bacteria and half by viruses. The relative proportion of bacterial causes may be higher among young children and viral causes higher in older persons.
Although a long list of viruses can inflame the conjunctiva, the usual offenders are the adenoviruses. This is a family of nearly fifty related viruses that also cause respiratory illness, such as colds or pneumonia. They also occasionally cause intestinal or urinary tract inflammation. Adenoviruses are common; most of us will have an illness with one by the age of ten. It is unclear exactly why adenoviral infections cause conjunctivitis at some times and not at others, but apparently several of the individual strains of virus are especially prone to do this.
The list of bacteria that commonly cause conjunctivitis is short: usually they are strains of bacteria termed pneumococci, haemophilus, or Moraxella. These bacteria are all common inhabitants of the respiratory tract, such as the nasal passages, where they cause no problems if they remain there. But when they invade the area around the eye, infection results. The students at Dartmouth all had infections from a species of pneumococci.
Both bacterial and viral conjunctivitis are spread the same way--by direct contact. The eye drainage from a typical case is highly infectious. Since a person with itchy eyes inevitably touches them frequently, the causative bacteria or virus gets transferred to fingers, which then touch other things. The attack rate for conjunctivitis, the percentage of susceptible persons who will get the infection if exposed to a person with it, is extremely high. Living close together, such as were the students in the Dartmouth dormitories, can lead to epidemics. Preschools are another common scene for outbreaks.
There are several less common infectious forms of conjunctivitis. A newborn infant can get conjunctivitis from micro-organisms called chlamydia that may be present in a mothers' birth canal and infect the child during birth. A particularly severe form of chlamydial eye infection is called trachoma. This malady is common in developing countries but is virtually never seen in the United States. Untreated gonorrhea in a mother can lead to a severe form of conjunctivitis in her infant, something once common in the United States, but which has been eliminated both by the overall decrease in the incidence of gonorrhea and by treatment of newborns' eyes with antibiotics soon after birth.
Wearers of contact lenses are prone to develop a special variety of conjunctivitis, termed giant papillary conjunctivitis. This condition is not an infection, but rather, is a reaction of the conjunctiva to chronic irritation of the contact lenses, particularly if the lenses are not thoroughly cleaned on a regular basis. The condition may prevent some persons from continuing to wear their contact lenses.
How is conjunctivitis diagnosed?
Like many medical conditions, conjunctivitis is a clinical diagnosis. This means there is no specific test for it; one simply looks at the characteristically inflamed conjunctiva and makes the diagnosis. As is also the case for many other medical conditions, the clinical history, what the patient tells the examiner, is key to solving the puzzle. If the person was exposed to anyone else who has eye complaints, this suggests infectious conjunctivitis. If the symptoms have happened before, especially on a windy day during pollen season, allergic conjunctivitis is likely. And if the person spent the previous afternoon scrubbing an enclosed shower stall with a powerful spray cleaner, has recently changed to a new contact lens solution, or spent twelve hours in a public swimming pool, then irritative conjunctivitis is a good possibility.
The different varieties of conjunctivitis overlap in their symptoms. However, allergic and irritative causes tend to produce less intense redness and less discharge from the eyes than do the infectious kinds. The discharge also tends to be more clear, thinner, and yellowish, when the cause is not an infection. Allergic conjunctivitis is often accompanied by other allergic symptoms, such as a runny nose. Both allergic and irritative forms generally affect both eyes equally. In contrast, infectious conjunctivitis usually begins in one eye or the other, although it typically spreads quickly to both eyes.
If the case looks to be an infectious one, culture of the eye drainage can be used to distinguish between viral and bacterial causes. This is not routinely done, however. For one thing, although the offending bacteria are easy to grow in the laboratory, growing viruses is a long and expensive process. A more important consideration is that, as a practical matter, the answer the culture gives does not affect treatment anyway. There are exceptions to this. Examples include complicated cases, such as an infection associated with an eye injury, or if the person's symptoms are not responding to usual treatment. Cultures also give useful information when dealing with an epidemic outbreak, such as the situation at Dartmouth.
How is conjunctivitis treated?
Both allergic and irritative conjunctivitis respond to the common-sense measure of avoiding the offending environmental agent. If elimination of exposure is not feasible, chronic allergic conjunctivitis can be helped by oral anti-allergy medications, such as anti-histamines, or by eye drops containing a medication called cromolyn. Irritative conjunctivitis can be soothed by over-the-counter saline eye drops, often called artificial tears. Moist compresses over the eyes, especially first thing in the morning, help loosen the dried crusts on the lashes and also soothe the burning and itching of any form of the disorder.
Infectious conjunctivitis is generally treated with antibiotic-containing eye drops or ointment. As noted above, the decision to treat is based upon what the patient tells the doctor and what the doctor sees when examining the eyes--cultures are rarely done. This means at least half the cases, the viral ones, will not be helped by the treatment because antibiotics have no activity against viruses. However, the risks of antibiotic therapy are very low, so treatment is unlikely to cause any harm.
Bacterial conjunctivitis generally goes away even without antibiotic treatment, usually within about five days. However, the symptoms will improve faster with treatment than without it. In addition, treatment renders a patient non-infectious to others within one to two days of starting the antibiotics. This is an important consideration for schools and daycare facilities. Good hand washing and proper disposal of tissues used to wipe the eyes are important additional measures that minimize the spread of the infection.
Several kinds of antibiotic drops or ointments are effective against the bacteria typically present in bacterial conjunctivitis. Drugs of the quinolone class of antibiotics, such as ciprofloxacin, are often used. Other effective eye drops contain gentamicin or sulfacetamide. Commonly used ointments contain one of the related drugs erythromycin or azithromycin. The decision to use drops or ointment is based on physician or patient preference; some persons find one or the other more tolerable, although neither treatment causes significant discomfort.
If the patient has symptoms atypical for ordinary conjunctivitis, such as severe eye pain or difficulty with vision, a referral to an ophthalmologist may be needed. Such a referral is also appropriate if the initial examiner suspects a complicated situation, such as an actual foreign body in the eye or injury to the eye, of if the patient has prolonged symptoms that do not respond to the usual measures.
What is the typical course of conjunctivitis?
Without any treatment, bacterial conjunctivitis usually lasts about five days, a day or two less with antibiotic treatment. The natural course of viral conjunctivitis is about the same as for bacterial cases.
Are there any long-term effects of conjunctivitis?
There are no long-term effects of simple conjunctivitis.
References and useful links
Martin M, Turco JH, Zegans ME, et al. An outbreak of conjunctivitis due to atypical Streptococcus pneumoniae. New Eng J Med 2003. 348:1112-21.
Sheikh A, Hurwitz B. Antibiotics versus placebo for acute bacterial conjunctivitis. Cochrane Colaboration
Silverman MA, Bessman E. Conjunctivitis
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