Acute red eye

At a glance

• Most acute red eyes are conjunctivitis or subconjunctival haemorrhage, both benign. The job is to catch the small group that will lose sight within hours to days.
• Four findings shift a red eye into the urgent group: reduced visual acuity, moderate to severe pain or photophobia, an abnormal pupil, and a corneal opacity or fluorescein staining.
• Contact lens wear, recent eye surgery or intravitreal injection, trauma and chemical exposure each warrant same-day ophthalmology.
• Measure visual acuity first in every patient (pinhole and glasses), except chemical injury, which is irrigated before anything else.

Causes

Cause	Pain	Vision	Key features
Bacterial conjunctivitis	Gritty	Normal	Mucopurulent discharge, lids stuck in the morning
Viral (adenoviral) conjunctivitis	Gritty	Normal or mildly blurred	Watery, follicles, tender preauricular node, recent URTI, very contagious
Allergic conjunctivitis	Itch	Normal	Bilateral, chemosis, atopy, seasonal
Subconjunctival haemorrhage	None	Normal	Flat bright red patch; check BP and INR if anticoagulated
Episcleritis	Mild	Normal	Sectoral redness, self-limiting
Scleritis	Severe, boring	May fall	Violaceous, tender globe, systemic disease
Anterior uveitis	Moderate, photophobia	Mildly reduced	Ciliary flush, small pupil, keratic precipitates, hypopyon
Keratitis	Moderate to severe	Reduced if central	Corneal opacity or staining, contact lenses, HSV dendrite
Acute angle closure	Severe, with headache and vomiting	Markedly reduced, haloes	Hazy cornea, mid-dilated fixed pupil, hard globe
Endophthalmitis	Severe	Markedly reduced	Days after cataract surgery or intravitreal injection, hypopyon
Orbital cellulitis	Pain on eye movement	May fall	Proptosis, restricted movement, fever, RAPD late

Focused history

• Onset and laterality. Bilateral and gritty suggests conjunctivitis. Unilateral, painful and photophobic suggests uveitis, keratitis or angle closure.
• Vision: blurring that doesn't clear with blinking is significant. Haloes around lights point to corneal oedema (angle closure).
• Contact lenses: type, overnight wear, swimming or showering in them (Acanthamoeba).
• Trauma: grinding or hammering metal means a possible intraocular foreign body; get an orbital X-ray or CT, not MRI.
• Recent surgery or intravitreal injection (endophthalmitis presents days later).
• Drugs: topiramate, anticholinergics, sympathomimetics, antidepressants (angle closure); anticoagulants (haemorrhage).
• Systemic disease: inflammatory back pain, IBD, psoriasis and reactive arthritis (HLA-B27 uveitis); RA and vasculitis (scleritis); sarcoidosis; HIV; sexual history (gonococcal and chlamydial conjunctivitis).

Focused examination

• Visual acuity with pinhole.
• Pattern of redness. Diffuse conjunctival injection, worst in the fornices, is surface disease. A ciliary flush (a ring of redness at the limbus) means intraocular inflammation or keratitis.
• Pupils: size, shape, reactivity, RAPD.
• Cornea: clarity, then fluorescein under blue light for abrasions, ulcers and dendrites.
• Anterior chamber: depth (shine a penlight from the side), hypopyon or hyphaema.
• IOP with a tonometer if available. Palpating a stone-hard globe through closed lids is crude but useful.
• Lid eversion for a subtarsal foreign body, eye movements, proptosis and preauricular nodes.
• Relief of pain with a drop of topical anaesthetic suggests surface disease. Pitfall: never send a patient home with anaesthetic drops. Repeated use causes corneal melt.

Red flags

• Reduced acuity, severe pain, photophobia (especially consensual photophobia, pain in the affected eye when light is shone in the other)
• Ciliary flush, fixed or irregular pupil, hazy cornea, corneal opacity, hypopyon
• Contact lens wearer
• Hyperacute copious purulent discharge (gonococcal)
• Neonate, immunosuppression, recent eye surgery
• Proptosis or painful eye movements

Management of the serious causes

Acute angle closure

Risk factors: hypermetropia, older age, female sex, East Asian ancestry, and dim light or drugs that dilate the pupil. Bilateral angle closure soon after starting topiramate is a separate mechanism (see the card).

While arranging emergency ophthalmology:

• Acetazolamide 500 mg IV (or orally if not vomiting). Caution in sulfonamide allergy, renal impairment and sickle cell disease; it causes hypokalaemia.
• Timolol 0.5% one drop and apraclonidine 1% or brimonidine 0.2% one drop.
• Pilocarpine 2% once IOP starts to fall, into the affected eye.
• Lie the patient supine, give analgesia and an antiemetic. IV mannitol if IOP stays high.
• Definitive treatment is laser peripheral iridotomy in both eyes, as the fellow eye is at high risk.

Pitfall: angle closure presenting with headache and vomiting gets worked up as migraine, subarachnoid haemorrhage or gastroenteritis. Look at the eye.

Microbial keratitis

• Contact lens wear is the main risk factor in Australia. Pseudomonas causes rapidly progressive ulcers; Acanthamoeba gives pain out of proportion and a ring infiltrate.
• Same-day ophthalmology for corneal scrapings, then hourly topical antibiotics (a fluoroquinolone or fortified antibiotics). Don't patch.
• HSV keratitis gives a branching dendritic ulcer on fluorescein. Antiviral treatment under ophthalmology (oral aciclovir or valaciclovir, or topical ganciclovir gel). Steroid drops make it much worse.
• Herpes zoster ophthalmicus: oral valaciclovir 1 g three times daily or famciclovir 500 mg three times daily for 7 days (the Therapeutic Guidelines zoster doses, not the lower 250 mg famciclovir dose in the Australian PI), started within 72 hours (still treat after 72 hours if new lesions are appearing or the eye is involved), plus ophthalmology review for keratitis, uveitis and raised IOP.

Anterior uveitis

• Recurrent unilateral attacks with HLA-B27 disease (ankylosing spondylitis, reactive arthritis, psoriatic arthritis, IBD). Granulomatous uveitis suggests sarcoidosis, TB or syphilis.
• Ophthalmology starts topical prednisolone acetate 1% and a cycloplegic (homatropine or atropine) to relieve ciliary spasm and prevent synechiae.
• Screen for an underlying cause when it's bilateral, granulomatous or recurrent: syphilis serology, ACE, chest X-ray, IGRA (TB must be excluded before systemic immunosuppression), HLA-B27.
• Checkpoint inhibitors, bisphosphonates and rifabutin can cause uveitis.

Scleritis

• Severe pain that wakes the patient, a tender globe and a violaceous hue. Vessels don't blanch with phenylephrine.
• Urgent ophthalmology plus a search for RA, GPA (ANCA), relapsing polychondritis, SLE and IBD.
• Treatment is systemic: oral NSAIDs for non-necrotising disease, high-dose corticosteroids and steroid-sparing immunosuppression (methotrexate, mycophenolate, cyclophosphamide or rituximab for vasculitis) for severe or necrotising disease.
• Episcleritis needs only lubricants or a short course of an oral NSAID, and rarely a systemic workup unless recurrent.

Endophthalmitis

• Post-operative (after cataract surgery or intravitreal injection) or endogenous (S. aureus bacteraemia, Klebsiella liver abscess, Candida with lines or injecting drug use).
• Emergency vitreous tap and intravitreal vancomycin plus ceftazidime. Endogenous cases also need systemic treatment and a search for the source, including echocardiography.

Chemical injury

• Irrigate at once with 1 to 2 L of saline (tap water if that's what's to hand), after topical anaesthetic. Check pH after 5 minutes and continue until neutral.
• Alkali (lime, cement, oven cleaner, drain cleaner) causes liquefactive necrosis and penetrates. Limbal blanching (white rather than red) is a bad sign.

The benign causes

• Bacterial conjunctivitis usually settles within 5 to 7 days without treatment. Chloramphenicol 0.5% drops shorten it modestly. Swab and refer if it fails to improve or the patient is a contact lens wearer.
• Hyperacute purulent conjunctivitis in a sexually active adult is gonococcal until proven otherwise: Gram stain and NAAT, systemic ceftriaxone, ophthalmology review (corneal perforation risk) and contact tracing. Chlamydial conjunctivitis is chronic and follicular and needs oral azithromycin.
• Adenoviral conjunctivitis lasts 2 to 3 weeks and is infectious for about 2 weeks. Hand hygiene, no shared towels, time off work. Antibiotics don't help.
• Allergic conjunctivitis: cold compresses, then topical antihistamine and mast cell stabiliser (olopatadine or ketotifen).
• Subconjunctival haemorrhage clears over 2 weeks. Recurrent episodes warrant a bleeding history; after trauma, a haemorrhage with no visible posterior limit suggests an orbital fracture.

Australian specifics

• Trachoma (Chlamydia trachomatis serovars A to C) persists in some remote Aboriginal communities. Australia is the only high-income country where it remains endemic. Control follows the WHO SAFE strategy: Surgery for trichiasis, Antibiotics (community azithromycin), Facial cleanliness and Environmental improvement. It's notifiable in most jurisdictions.
• In rural and remote areas, ophthalmology advice is often by phone or telehealth with photos. Send acuity, pupil findings, fluorescein appearance and IOP if measured.

Pitfalls

• Topical steroids prescribed for a red eye before a slit-lamp examination can be disastrous in HSV keratitis.
• A unilateral painful red eye in a contact lens wearer is keratitis until proven otherwise. Don't treat it as conjunctivitis.
• Pupil-dilating drugs (anticholinergics in delirium, nebulised ipratropium with salbutamol, adrenaline) can precipitate angle closure in a predisposed eye.
• In ICU, red eyes in sedated patients are often exposure keratopathy from incomplete lid closure. Lubricate and tape.
• Never patch an eye with a corneal abrasion from a contact lens.
• Orbital cellulitis needs CT and IV antibiotics. Proptosis, painful or restricted eye movements and reduced acuity separate it from preseptal cellulitis.