Conjunctivitis (Pink Eye)

What causes conjunctivitis?

Infectious conjunctivitis is almost always caused by viruses and bacteria.

Viral cases, comprising 70-80% of pink eye, are usually due to the adenovirus family, which also sometimes causes colds, bronchitis, and intestinal infections. Less commonly (in about 1-5% of cases), the herpes family of viruses can cause a more severe conjunctivitis.

Bacterial cases are predominantly caused by the same bacteria that can be involved with ear and sinus infections.

Also, newborns are vulnerable to a different subset of causative organisms in the first two weeks postpartum, which is the reason most babies receive antibiotic ointment on their eyelids shortly after birth.

How is it diagnosed?

Symptoms include pink or red eyes, sometimes with eyelid swelling; a gritty, painful, or itchy sensation; and ocular tearing or discharge. Diagnosing conjunctivitis is not typically difficult, though determining what caused it can be.

Bacterial cases tend to have thicker discharge that persists throughout the day and spontaneously re-accumulates after cleansing.

Viral cases are sometimes associated with cold symptoms, like sore throat or cough, and are more likely to cause enlarged lymph nodes. Other distinguishing features are of variable accuracy in studies.

What other conditions might be confused for pink eye?

Allergic conjunctivitis is the most common condition that may look similar. It can be seasonal and may be associated with other allergy symptoms.

Red eyes can also be caused by injury or irritation (corneal abrasion, chemical conjunctivitis, capillary hemorrhage, and dry eye) or by deeper inflammatory or infectious conditions (keratitis, iritis, scleritis, and acute angle closure glaucoma).

What are warning signs for a more serious infection or condition?

Moderate-to-severe eye pain, sensitivity to light (photophobia), and reduced visual acuity are findings that are not typically seen with conjunctivitis and could be a sign of a more serious condition that needs an urgent ophthalmology consultation.

Herpes and zoster (the virus that causes chickenpox and shingles) should be suspected in cases of decreased facial sensation or facial pain on the involved side; a rash on the same side or the tip of the nose is another indicator. These conditions benefit from rapid diagnosis and appropriate treatment.

Is there a test for conjunctivitis?

Most cases of conjunctivitis don't require testing, and are diagnosed by history alone. However, there are tests available for adenovirus, the most common cause of pink eye.

One of these, a point-of-care test, has good diagnostic specificity, but has not consistently demonstrated high sensitivity—studies have shown it detects about 50% of cases. Therefore, medical offices and hospitals have not adopted it into widespread use. There are other more accurate tests, but the usual result turnaround time of three-to-four days is not fast enough to influence most treatment decisions.