Conjunctivitis, or pink eye, is  the inflammation of the conjunctiva, the thin membrane that covers the inside of the eyelids and the white part of the eye. Conjunctivitis can be caused by an infection, an irritant or an allergy.

Symptoms of conjunctivitis
Conjunctivitis is associated with quite a range of symptoms, which vary according to what is causing the problem. The most common ones are:

  • Pink eyes or red eyes: inflammation causes blood vessels on the surface of the eye to expand, so it looks red. It is important to get medical attention if you have red eyes that are sore and painful and that are also sensitive to light as the problem may be something more serious than pink eye.
  • Irritated eyes: your eyes feel irritated, prickly and uncomfortable but not really painful. Pain can be a sign of more serious eye conditions such as keratitis.
  • Discharge that can crust the eyelids: this can be heavy and greenish if you have a bacterial eye infection; viral conjunctivitis tends to produce a lighter, watery discharge.
  • Itchy eyes: along with sore eyes, teary eyes, and a stuffy, runny or itchy nose, eyes that itch so that you want to rub them constantly usually indicate you have allergic conjunctivitis.

Only one eye can be affected, or the symptoms can spread to both eyes; this is more common in bacterial conjunctivitis compared to viral conjunctivitis.

What causes infectious conjunctivitis?
Most commonly bacteria and viruses are responsible; fungi and parasites rarely cause superficial eye infections.
Simple bacterial conjunctivitis is most often caused by a member of the Staphylococcus species, or by Streptococcus pneumoniae, Haemophilus influenzae, or Moraxella catarrhalis. Chronic chlamydial conjunctivitis is common in adults and chlamydia infection is the most usual cause of eye infection in newborns. More rarely, cases of gonococcal conjunctivitis can occur in babies born to mothers who have gonorrhoea, which is due to infection with Neisseria gonorrhoeae.

Viral conjunctivitis is commonly due to an adenovirus infection. As well as eye symptoms, this can cause fever and a sore throat and some types of adenovirus can cause keratitis. Two types of herpes virus, herpes simplex (the usual cause of cold sores) and herpes zoster (the virus responsible for chicken pox and shingles), both lie dormant in the nerves of the body, held in check by the immune system. Both can track back down the peripheral nerves in the face and erupt, causing blisters on the face and head and in the conjunctiva.

Molluscum contagiosum is a common viral skin infection that can spread to the eyes. It often causes conjunctivitis in very young children before they acquire resistance to the virus that causes it. People who are immunocompromised such as those with AIDS, people undergoing cancer treatment or who have had an organ transplant followed by immunosuppressant drugs can also develop this type of viral conjunctivitis. These groups are also susceptible to fungal eye infections, which normally don’t take hold in someone with a healthy immune system.  It is rare for parasites to infect the eyelids but lice can infest the eyelashes causing conjunctivitis.

What causes allergic conjunctivitis?
Several different allergens can provoke an allergic response in the lining of the eyelids:

  • Seasonal conjunctivitis is associated with hay fever and pollen allergy.
  • Perennial conjunctivitis causes symptoms throughout the year and is often caused by allergies to house dust mites and animal dander.
  • Giant papillary conjunctivitis can develop in people who wear non-disposable contact lenses or who have had eye surgery.
  • Contact dermatoconjunctivitis is often a response to eye drops, chemicals or cosmetics.
  • Vernal conjunctivitis is a rare chronic condition that affects people with a family history of allergies.

Causes of irritant conjunctivitis
Eye inflammation can develop if smoke, fumes, grit or eyelashes get into the eye. When the irritant is removed, the inflammation subsides.

Soothing conjunctivitis
General approaches to easing symptoms include:

  • Discontinuing contact lens wear until all signs of inflammation have gone.
  • Cleaning any discharge away with cotton wool and clean water (boiled and cooled water is best).
  • Avoid rubbing your eyes; a cool compress and lubricant eye drops may also help.

Specific treatment then aims to tackle the underlying cause as well as reduce symptoms and prevent inflammation reaching the cornea.