Red eye

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

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.

Acute painful red eye symptoms

Acute non-painful red eye symptoms

The non-acute red eye²

Adnexal causes

• Blepharitis

• Trichiasis/distichiasis

• Floppy eyelid syndrome

• Lagophthalmos

• Dacryocystitis

• Canaliculitis

• Acne rosacea

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

• Dry eye syndrome.

• Carotid-cavernous sinus fistula.

• Cluster headaches.

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.