Red Eye

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PatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.

See also: Visual Problems written for patients

Red eye is a common presentation in primary care and is a sign of inflammation. Most cases will be due to relatively benign problems. The most common cause of red eye presenting in a primary care setting is conjunctivitis.[1] A small proportion of red eye cases are serious and need urgent treatment. The challenge lies in discerning one from the other.

This article looks at the diagnostic algorithms which help health professionals distinguish the benign from the more serious, and reviews the conditions which should be considered in the diagnostic sieve. More detailed information on specific conditions and their management can be found in the linked articles.

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Common benign causes of red eye include conjunctivitis, blepharitis, corneal abrasion, foreign body, subconjunctival haemorrhage, keratitis, iritis, uveitis, glaucoma, chemical burn, radiation burn, episcleritis and scleritis. Watering, soreness and discharge are common.

History of presenting complaint

  • Time and speed of onset
  • Ocular symptoms (eg, pain, photophobia, blurred vision, discharge, etc).
  • Systemic symptoms (eg, headaches, nausea, a rash on the forehead).
  • Symptoms affecting the other eye.
  • Specifically enquire about trauma, however minor it appears to have been.
  • Recent contact with infectious illness (eg, herpes simplex, conjunctivitis).

Past ocular history

  • Any other episodes.
  • Ophthalmic surgery.
  • Lazy eye.
  • Whether they wear, or have they worn, contact lenses. Whether lens care/hygiene could be an issue.

Social history

  • Determine whether the eye condition is affecting activities of daily living.
  • Establish whether there is an immediate management problem.
  • Ask whether the patient drove to the surgery. Establish whether they are fit to drive away again.


It is essential to record the visual acuity (VA) - in both eyes - and to carry out a careful anatomical examination. Begin the examination anteriorly and work your way backwards. Pupils and their reactions should also be checked. See separate Examination of the Eye article.

If no ocular causes of a red eye emerge, consider potential systemic causes, a review of the patient's past medical history and a full physical examination. Scleritis and, much less commonly, episcleritis, are frequently associated with connective tissue diseases - particularly rheumatoid arthritis, gout, syphilis and, less commonly, tuberculosis, sarcoidosis and hypertension.

For diagnostic purposes the causes of red eye are commonly divided into those which are painful and those which are not.

Suspected condition
Common symptoms
Common signs
Referral urgency
Acute angle-closure glaucomaSeverely painful, haloes around point light sources, photophobia, watering. Patient may be systemically unwell (nausea, vomiting, headache). Usually aged >50 years.Decreased VA, hazy cornea, fixed, semi-dilated or oval pupil.Refer immediately.
KeratitisPhotophobia, foreign body (FB) sensation ± history of contact lens wear ± previous episodes (eg, herpes simplex infection).VA depends on the exact nature of the problem - peripheral lesions may cause little change but some decrease is expected. Corneal defect on staining ± hypopyon (pus seen in anterior chamber).Within 24 hours.
Acute anterior uveitisPhotophobia, blurred vision, headache, pain on accommodating. May have been unresponsive to previous treatment for conjunctivitis.VA may be reduced, redness more localised around the corneal edge (ciliary injection), pupils may be constricted or irregular. When severe, white cells precipitate on the corneal endothelial surface (seen as white clumps - keratic precipitates).Within 24 hours.
Trauma - eg, FB or corneal abrasionPain depends on the type of trauma, severity and location.Depends on the trauma.The patient needs to have a full slit-lamp examination - refer immediately if risk of serious trauma/penetrating injury.
ScleritisSevere boring-type eye pain, gradual onset. Possible radiation to forehead or jaw. Progressive onset of photophobia and visual impairment.In anterior disease there may be diffuse deep injection but in posterior scleritis this may be minimal. Suspect in patients over 50 with systemic conditions such as connective tissue disease, gout, previous herpes zoster ophthalmicus.Refer within 24-48 hours for treatment under ophthalmological supervision. 
EndophthalmitisRed eye, decreasing VA and pain in context of recent surgery, trauma, intravenous drug use or immune compromise.Hypopyon in the anterior chamber visible with patient upright. Hazy anterior chamber. Conjunctival chemosis and eyelid oedema.Urgent/immediate referral for intravitreal and systemic antibiotics. Rare but potentially devastating.

Suspected condition
Common symptoms
Common signs
ConjunctivitisGritty or itchy discomfort (if there is moderate-to-severe pain - suspect more serious pathology); photophobia is rare unless there is a severe form of adenoviral infection which may involve the cornea, discharge ± history of contact ± history of allergen exposure.Normal VA unless there is corneal involvement, unilateral or bilateral, discharge in infective conjunctivitis, follicles or papillae; may be eyelid swelling ± conjunctival oedema.Refer if this fails to settle or respond to treatment (over 7-10 days) or if there is suspicion of herpetic infection.
EpiscleritisMild discomfort, few symptoms.Normal VA, localised patch of redness/injection which blanches on application of a drop of phenylephrine 2.5%. No discharge.Refer if there is more than slight discomfort or if it fails to settle spontaneously over ~ 1 week.
Subconjunctival haemorrhageMay be spontaneous or traumatic; can occur after prolonged coughing. Usually asymptomatic, although some patients notice mild aching.Blood under conjunctiva, covering part or all of the eye which is otherwise quiet with normal VA.

Refer if traumatic. If not, check blood pressure in elderly patients (can occur with hypertension) and reassure: should resolve over a fortnight.

Adnexal causes

Conjunctival causes

  • Medication toxicity - see separate Eye Drugs - Prescribing and Administering article.
  • Inflamed pinguecula - a pingueculum is a common, innocuous lesion seen as a cluster of yellow-white deposits (usually in a triangular formation with the base adjacent to the cornea), arranged temporally or nasally to the cornea. It results from degenerative change in the sclera from environmental irritants, including sunlight. If it becomes inflamed (pingueculitis), it becomes red and may be elevated, sore or ulcerated.
  • Less common but serious causes include Stevens-Johnson syndrome, cicatricial pemphigoid and (rarely) conjunctival neoplasia.

Corneal causes

It is unusual for a corneal condition to present as a chronic red eye problem, although acute-on-chronic problems are often seen - eg, a long-standing pterygium which has become inflamed, recurrent corneal erosion syndrome and cases of recurrent keratitis (such as marginal keratitis or herpes simplex infection). Patients are often familiar with their condition and its management.

Other causes

Urgent referral is warranted for potentially serious problems. Features suggestive of a serious condition which may warrant urgent referral include:

  • Moderate-to-severe eye pain or photophobia.
  • Marked unilateral redness. The greater the redness, the more likely it is that the cause is serious.
  • Ciliary injection, which is not always obvious, is suggestive of inflammation of deeper structures. It is indicated by redness and dilated blood vessels that can be seen between the sclera and the iris.
  • Reduced VA.
  • Photophobia or seeing coloured haloes around point sources of light.
  • Copious purulent discharge (particularly in neonates).
  • Corneal involvement.
  • Known or suspected eye trauma.
  • Recent ocular surgery.
  • Pupillary distortion or abnormal reaction.
  • Herpes simplex or herpes zoster.
  • Recurrent episodes.
  • Proptosis.
  • Contact lens wear.

Chemical burns are an ophthalmic emergency and should be immediately irrigated before any steps are taken. Common agents include cement, plaster powder and oven cleaner, all of which are alkaline. Refer once pH has stabilised, even if there are no residual symptoms. See separate Eye Injuries article.

Further reading & references

  1. Cronau H, Kankanala RR, Mauger T; Diagnosis and Management of Red Eye in Primary Care, American Family Physician. 2010 Jan 15;81(2):137-144
  2. Red eye; NICE CKS, September 2012 (UK access only)
  3. Common ocular emergencies and referrals; Eye Casualty website

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Dr Olivia Scott
Current Version:
Peer Reviewer:
Dr Colin Tidy
Document ID:
1694 (v24)
Last Checked:
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