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Red eye

Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find the Eye problems article more useful, or one of our other health articles.

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What causes red eye?

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 conjunctivitis1 . 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.

Assessment of the red eye2

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).

  • Sensation of a foreign body.

  • Itch.

  • 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).

  • Recent chemical exposure.

Past history

  • Any other episodes.

  • Any history of ophthalmic surgery.

  • Lazy eye.

  • Whether they wear, or have they worn, contact lenses. Whether lens care/hygiene could be an issue.

  • Any history of hypertension or conditions associated with red eye (eg, connective tissue disorders, atopy, autoimmune conditions).

  • Any recent illnesses.

  • Any family history of eye conditions, or other relevant conditions.

  • Use of medication (for example, use of eye drops) - if subconjunctival haemorrhage is suspected, determine if the person is taking an anticoagulant.

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.

Examination of red eye

If perforation of the globe is suspected (history of trauma or complication of scleritis) do not palpate the eye but arrange for urgent ophthalmological assessment2 .

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.Check for facial trauma. See the 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.

Continue reading below

Acute painful red eye symptoms

Suspected condition

Common symptoms

Common signs

Referral urgency

Acute angle-closure glaucoma

Severely 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.


Photophobia, 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 uveitis

Photophobia, 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 abrasion

Pain 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.


Severe 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.


Red 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.

Acute non-painful red eye symptoms

Suspected condition

Common symptoms

Common signs



Gritty 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.


Mild 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 haemorrhage

May 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.

Continue reading below

The non-acute red eye2

Adnexal causes

Conjunctival causes

  • Medication toxicity - see the 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.

Child maltreatment

Although rare, suspect this in a child with retinal haemorrhages, injury to the eye in the absence of major confirmed accidental trauma or a known medical explanation, including birth-related causes.

Other causes

Red eye treatment and management2

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

  • Acute glaucoma

  • 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 laceration.

  • Corneal foreign body.

  • Intraocular foreign body.

  • Corneal ulcer.

  • Contact lens-related ulcer.

  • Known or suspected eye trauma.

  • Endophthalmitis.

  • Recent ocular surgery.

  • Pupillary distortion or abnormal reaction.

  • Herpes simplex or herpes zoster.

  • Neonatal conjunctivitis.

  • 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 the separate Eye Injuries article.

Refer within 24 hours for:

  • Anterior uveitis

  • Scleritis

For conditions not requiring urgent referral
Manage appropriately in primary care (see links to individual conditions in Assessment section).

Dr Mary Lowth is an author or the original author of this leaflet.

Further reading and 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, May 2021 (UK access only)

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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