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There are many causes of a red eye. Below we have outlined the commonest and most important causes.
Causes of a red eye:
  1. Conjunctivitis
  2. Corneal abrasions and ulcers
  3. Acute Iritis
  4. Scleritis
  5. Acute Glaucoma (separate notes available)
  6. Subconjunctival haemorrhage


  • Gritty irritation/itchiness, watery/purulent discharge, diffuse injection
  • Intensity of injection around the periphery suggests conjunctival inflammation whereas injection around the cornea suggests corneal or intra-ocular inflammation.
  • Usually bilateral
  • Infective causes:
  • Bacteria – more purulent discharge where eyelids may stick together
  • Viruses – adenovirus is very infectious, small lymphoid aggregates appear as follicles on conjunctiva, pre-auricular lymph node enlargement
  • Chlamydia – young adults or newborns (opthalmia neonatorium is caused by bacteria in the birth canal and must be treated immediately to preserve eyesight)
  • Allergy
  • Vision is normal or very mildly reduced
  • Treatment depends on the cause: allergic conjunctivitis may respond to antihistamines or self resolve when the allergen is removed, antibiotics clear bacterial conjunctivitis, and viral conjunctivitis will disappear on its own.

Corneal Abrasion

  • This occurs when the surface epithelium is sloughed off – usually due to trauma
  • Pain, foreign body sensation, tearing, red eye
  • Variable reduction in vision
  • Stains with fluorescein
  • Treatment: Analgesia (paracetamol or ibuprofen), Prevention of secondary infection with tetanus prophylaxis and a topical antibiotic for 7 days (chloramphenicol or fusidic acid)
  • Exclude a foreign body which may be trapped under the inside of the upper eyelid. (Invert the upper eyelid over a cotton bud or orange stick.)
Corneal Abrasion
Corneal Abrasion – Image from Wikipedia

Corneal Ulceration

  • Bacterial: Chlamydia, Pseudomonas
  • Viral: Herpes Simplex virus (causes a dendritic ulcer), Herpes Zoster virus
  • Fungal: candida, aspergillus
  • Protozoan: Acanthamoeba in contact lens wearer
Mechanical or trauma. Check for foreign bodies.
Chemical:Alkali injuries are worse than acid – seconds count
Ulceration with keratitis (inflammation of the cornea) is known as ulcerative keratitis and must be treated as an emergency to prevent permanent scarring or visual loss.

Anterior uveitis (iritis)

Inflammation of the anterior uvea, comprising the coloured iris and ciliary body.

Photophobia, cirumcorneal redness (due to ciliary congestion), acute pain,  lacrimation, decreased vision (due to precipitates in the aqueous), small pupil (due to iris spasms and adhesions)
Most commonly idiopathic
Associated with systemic disease

Positive Talbot’s test: pain increases as the eyes converge and pupils constrict (ask the patient to watch their finger approach their nose)
May be complicated by cataract or glaucoma
Often recurs in the same eye
Anterior Uveitis - Hypopyon
The exudate in the cornea seen in anterior uveitis – known as hypopyon. Image from wikipedia


  • Superficial irritation and inflammation of the episclera, a thin layer of tissue covering the sclera of the eye.
  • Idiopathic, collagen vascular disorder (Rheumatoid Arthritis). It occurs without an infection.
  • Asymptomatic, mild pain
  • Self-limiting without treatment within 1-2 weeks or topical corticosteroid eye drops may relieve the symptoms faster. Rarely, scleritis may develop.


Inflammation of the sclera causes a severely deep boring pain that wakes the patient at night, lacrimation, photophobia

  • Idiopathic
  • Collagen vascular disease (Rheumatoid Arthritis, Ankylosing Spondylitis, Systemic Lupus Erythematosus, Wegener’s granulomatosus, Polyarteritis nodosa)
  • Herpes Zoster
  • Sarcoidosis
  • Inflammatory Bowel Disease
  • Gout

Systemic treatment with NSAIDs (or oral Prednisolone if severe)

  • Corticosteroid eye drops/ oral corticosteroids help reduce the inflammation. Consider investigating for or treating the underlying cause to prevent recurrence.

Subconjunc​tival haemorrhage

  • Diffuse or localised collection of blood under conjunctiva – looks alarming but resolves sponatenously within 10-14 days
  • Asymptomatic
  • Causes: Idiopathic, trauma, cough, sneezing, aspirin, hypertension

Subconjunctival Haemorrhage
Subconjunctival Haemorrhage. Image from Wikipedia


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