Although the majority of patients with red eye can be managed in primary care, a few significant pathologies need prompt attention from an eye department.
Redness results from one of two things: a burst blood vessel or an inflammatory response involving the front of the eye.
Bleeding is usually the result of minor trauma to exposed conjunctival blood vessels. However, if extensive, subconjunctival haemorrhage can indicate a generalised clotting problem, raised orbital venous pressure or extension of a retro-orbital haematoma. All three are rare and should be apparent on systemic enquiry.
Inflammatory red eye can be divided into superficial conditions (usually managed in primary care) and deep (those that need referral).
Superficial exposed surfaces, such as the eyelid margin, conjunctiva and cornea may develop infective, toxic or allergy-based inflammation.
Our natural eye defences include an antibacterial and antiseptic tear film and locally-produced antibodies. The inflammatory response to environmental insult is swift and effective with excess tearing, hyperaemia and localised chemosis mediated by mast cell degranulation and release of vaso-active peptides.
Infection or irritation of eyelid margin glands (blepharitis) can give rise to localised swellings and meibomian cysts (chalazia) or styes.
Conjunctivitis is caused by viral or bacterial infection, allergens or irritants. Intra-corneal inflammation is rare, but red eye is caused by corneal viral infection such as herpes simplex; by corneal abscess; or by the painful stimulation accompanying corneal trauma or foreign body.
Inflammation of deep ocular structures is often associated with systemically-mediated autoimmunity and may manifest as part of a systemic disorder.
Episcleritis may be associated with gout, scleritis with polyarteritis nodosum and Wegener’s granulomatosis; and iritis with a wide range of systemic inflammatory disorders such as sarcoidosis, Crohn’s disease and ankylosing spondylitis.
Unique among causes of red eye is acute angle closure glaucoma.
In acute glaucoma, sudden mechanical obstruction to normal outflow of intra-ocular fluid (aqueous humour) at the drainage angle causes high intraocular pressure and stimulates a potent inflammatory response.
The safest and best way of diagnosing red eye is by full ophthalmic history and examination.
Three aspects to the clinical history that help distinguish between superficial and deep inflammation, vision, pain and recent history of eye surgery.
If eyesight is unaffected, the problem is probably self-limiting. Deep pain indicates probable deep pathology, but acute corneal problems are always painful. Recent history of eye surgery, significant ocular disease or soft contact lens wear should lower threshold for serious eye disease.
Use a pen-torch and look for the pattern of redness. If it is localised to the inferior conjunctiva this may indicate a toxic reaction to drops. If it is localised around the corneal edge, this may indicate intra-ocular inflammation. Look for a foreign body and big follicles in the conjunctivae if allergic or infectious conjunctivitis suspected. If the pupil is an odd shape this may indicate previous or current intra-ocular inflammation.
Is there sensitivity to light? This may be photophobia of iritis. Is the cornea clear? Use fluorescein stain to delineate corneal disturbance.
The age of the patient skews the odds to favour particular diagnoses. Most acute bacterial conjunctivitis occurs in pre-pubertal children. In an infant under four-weeks old, purulent conjunctivitis is notifiable because of the serious potential for neonatal infection with Chlamydia or Gonococcus to cause loss of sight. Adults with iritis are usually under 40, and those with acute glaucoma over 60 years of age.
Superficial conditions benefit from simple lid hygiene, because it removes any environmental irritants that promote inflammation.
Daily eyelid margin cleansing removes dried crusts and pathogens and improves the quality of the tear film. It involves gently rubbing along the lid margin with cotton wool soaked in warm water or very mild baby shampoo, followed by bland topical moisturiser. In some cases, this will resolve symptoms completely.
Specific antibacterial therapy will improve the speed of resolution in bacterial conjunctivitis, but has been shown not to be essential for cure.
Antibiotic drops are usually recommended for viral conjunctivitis to reduce the risk of bacterial superinfection. Topical antihistamines and NSAIDs drops are useful for symptoms of blepharitis and allergic eye disease, but they must be combined with long-term lid hygiene to prevent any recurrences.
In conjunctivitis associated with atopy, topical mast cell stabilisers are useful prophylaxis.
Red eye caused by topical medication is a common feature of eye casualty departments. Care must be employed prescribing antibiotics, tear supplements, glaucoma therapies and eyedrops containing preservatives to an elderly population (relative tear film deficiency) or patients who use contact lenses.
Painless red eye after a new eye drops prescription should be assumed to be a reaction and the toxicity treatment should be stopped.
Corneal problems are difficult to treat safely without slit lamp examination.
Uncomplicated corneal abrasion may be treated with a topical antibiotic with or without an eye pad for 24-hours, but persistent symptoms, a history of possible intraocular trauma, foreign body or chemical injury should prompt referral for full ophthalmic care.
Herpes simplex keratitis (dendritic ulcer) may respond to topical aciclovir five times daily, but may be associated with anterior uveitis, which requires topical steroids for resolution. This is best cared for in a specialist corneal clinic.
The intraocular conditions are all best treated in an eye clinic. Acute glaucoma requires iris surgery but it is helpful for antiemetics and painkillers to be given in primary care if there is delay reaching the eye clinic.
Finally, scleritis often requires systemic immunosuppression. Initial therapy with systemic steroids is best in a hospital environment.