Conjunctivitis is inflammation of the conjunctiva. The conjunctiva is a thin layer of tissue that covers to inside of the eyelids and the sclera of the eye. There are three main types:

  • Bacterial
  • Viral
  • Allergic


Conjunctivitis presents with:

  • Unilateral or bilateral
  • Red eyes
  • Bloodshot
  • Itchy or gritty sensation
  • Discharge from the eye

Conjunctivitis does not cause pain, photophobia or reduced visual acuity. Vision may be blurry when the eye is covered with discharge, however when the discharge is cleared the acuity should be normal.

Bacterial conjunctivitis presents with a purulent discharge and an inflamed conjunctiva. It is typically worse in the morning when the eyes may be stuck together. It usually starts in one eye and then can spread to the other. It is highly contagious.

Viral conjunctivitis is common and usually presents with a clear discharge. It is often associated with other symptoms of a viral infection such as dry cough, sore throat and blocked nose. You may find tender preauricular lymph nodes (in front of the ears). It is also contagious.


Differential Diagnosis of Acute Red Eye

A common exam topic and clinical challenge is to differentiate between the causes of an acute red eye. The more serious differentials tend to cause pain and reduced visual acuity.

Painless Red Eye

  • Conjunctivitis
  • Episcleritis
  • Subconjunctival Haemorrhage

Painful Red Eye

  • Glaucoma
  • Anterior uveitis
  • Scleritis
  • Corneal abrasions or ulceration
  • Keratitis
  • Foreign body
  • Traumatic or chemical injury



Conjunctivitis usually resolves without treatment after 1-2 weeks.

Advise on good hygiene to avoid spreading (e.g. avoid sharing towels or rubbing eyes and regularly washing hands) and avoiding the use of contact lenses. Cleaning the eyes with cooled boiled water and cotton wool can help clear the discharge.

If bacterial conjunctivitis is suspected then antibiotic eye drops can be considered, however bear in mind it will often get better without treatment. Chloramphenicol and fuscidic acid eye drops are both options.

Patients under the age of 1 month of age with conjunctivitis need urgent ophthalmology review as neonatal conjunctivitis can be associated gonococcal infection and can cause loss of sight and more severe complications such as pneumonia.


Allergic Conjunctivitis

Allergic conjunctivitis is caused by contact with allergens. It causes swelling of the conjunctival sac and eye lid with a significant watery discharge and itch.

Antihistamines (oral or topical) can be used to reduce symptoms.

Topical mast-cell stabilisers can be used in patients with chronic seasonal symptoms. They work by preventing mast cells releasing histamine. These require use for several weeks before showing any benefit.


Last updated April 2019