An infected eye can look pink or red, glassy or goopy, swollen or even a little bit black-and-blue. Many of these infections in the eye fall under the general umbrella of conjunctivitis. This term comes from the conjunctiva, which is the mucous membrane on the inside of the eyelid. Although the infection often shows up on the white part of the eye (the sclera), the real site of irritation is usually underneath the lid.
Not all eye infections are conjunctivitis. The conjunctiva has to be inflamed for the label to apply.
Conjunctivitis is typically very contagious. It is passed when a child with the infection rubs his eyes and then touches something else — a toy, a door handle, or your mouth. Infections that cause pinkeye can also cause other forms of illness, such as an ear infection or a classic “cold” (also known as an upper respiratory infection, or URI, with its runny nose, cough, and general malaise). Therefore, from the same underlying infection, one child may develop pinkeye and another may get a cough and a runny nose.
Conjunctivitis can be caused by either a virus or bacteria. With both types of infection, the eyes may look pink or red, making it difficult to tell which is the underlying cause: bacteria or virus.
There are, however, some classic features that distinguish viral from bacterial conjunctivitis. Eyes with viral conjunctivitis typically stream clear, watery tears. Eyes with bacterial conjunctivitis often have a thick yellow or green discharge. Viral conjunctivitis tends to be accompanied by a clear runny nose and a mild cough. Bacterial conjunctivitis is usually either an isolated infection or is accompanied by a green runny nose, sinus pain, a thick or deep cough, or swollen and itchy lids.
Why does the distinction matter?
The treatments for viral and bacterial conjunctivitis are different, as are the potential complications. Sometimes an eye infection is not isolated to the eyes. For instance, bacterial conjunctivitis often occurs together with an ear infection. Because the eyes and ears are connected via the sinuses, an infection in one place can spread to the other.
There are certainly many causes of pink eyes that are not conjunctivitis. Allergies can cause the whites of the eyes to look pink while the conjunctivas look normal. An eye injury, such as having been hit in the eye, can cause discoloration, although this is more often in the form of a bright red spot from a broken blood vessel. Irritants that come into contact with the eyes can cause watering and a pink discoloration. Soap, shampoo, pollen, lemon juice, and other acidic liquids also can result in pink eyes. None of these is conjunctivitis.