A bacterial conjunctivitis is the most common form, and is due to bacteria infecting the thin film of tears that covers the eye.
It is very easily passed from one person to another (e.g. a patient rubs their eyes with a hand, then shakes hands, and the second person then rubs their eyes). Babies suffering from a blocked tear duct may have recurrent infections.
Tears are produced in the lacrimal gland beyond the outer edge of the eye, move across the eye surface and then through a tiny tube at the inner edge of the eye that leads to the nose. If the duct is too small in an infant, or is blocked by pus or phlegm, the circulation of tears is prevented and infection results.
A number of viruses may infect the cornea to cause conjunctivitis. This form is not quite as easily transmitted as bacterial conjunctivitis.
Bacterial conjunctivitis causes the formation of yellow or green pus in the eyes, which may stick the eyelids together. The eyes are bloodshot and sore, and almost invariably the infection involves both eyes. If allowed to persist, it may cause scarring of the eye surface and a deterioration in sight.
Viral conjunctivitis causes slight pain or an itch, redness of the eye and often a clear sticky exudate.
Rarely, resistant infections make it necessary to take a swab from the eye to determine the exact bacteria or virus responsible, but in most cases, no investigations are necessary.
Bacterial conjunctivitis is easily treated with antibiotic drops or ointment on a regular basis until the infection clears, usually in two to four days. Children must be excluded from school until all eye discharge has ceased. A blocked tear duct may be probed and cleared if conjunctivitis persists in a baby for several months, but most grow out of the problem.
Viral conjunctivitis is the more difficult form to treat as there is no cure for most viral infections, but Herpes virus infections can be cured by antiviral drops. Soothing drops and ointment may be used, but time is the main treatment, and the infection may persist for several weeks until the body’s own defences overcome it.
Allergic (vernal) conjunctivitis is a reaction on the surface of the eye to a pollen, dust, chemical or substance to which the patient has an allergy. The eye becomes red, itchy and watery. Vasoconstrictor or antihistamine eye drops can be used to control the condition.