Red eye is one of the most common eye presentations you will encounter. Whilst many will likely be referred to an opthalmologist or senior clinician, it's important to know what common cases you are likely to encounter and how to manage them.

One of the main factors is to distinguish whether the red eye is or is not associated with pain. A table of causes of pain and painless red eyes covered in this article can be found below.

Painful Painless
Foreign bodies Blepharitis
Corneal abrasion Conjunctivitis
Corneal ulcer Subconjunctival haemorrhage
Scleritis Episcleritis
Anterior uveitis Dry eye
Endophthalmitis

As you will see, many of the conditions can be treated with topical antibiotics. Most causes of red eye will also benefit from topical lubricants. Do not prescribe topical steroids before discussing with ophthalmology. Never give patients topical anaesthetic drops to take home - this will delay epithelial recovery, and will mask any worsening of the condition.

Red eye with pain alert-info
Foreign bodies:
  • May be visible on the surface of the eye or embedded within the cornea or sclera. 
  • Associated clinical features include: Redness, Pain, Watering, ‘Foreign body sensation’
  • Foreign bodies may be hidden under the top and bottom of the eyelid, so always evert the upper & lower lids and check the fornices
  • Can be removed with a 21G needle and topical anaesthetic (e.g. proxymetacaine) at the slit lamp
  • Remember to use preservative-free povidone iodine eye drops pre and post removal of foreign body
  • Any residual rust ring can be removed after a minimum of 48hrs - refer to ophthalmology to arrange follow up
  • Prescribe chloramphenicol ointment QDS for 5 days

Corneal abrasion:
  • Superficial corneal epithelial defect
  • Can be hard to see with the naked eye but stain brightly with fluorescein drops and a cobalt blue light
  • Common clinical features: Eye redness, Pain, Watering, Photophobia
  • The majority usually heal within 1 week
  • Refer non-healing, recurrent or large abrasions (>50% of the cornea) to ophthalmology
  • Prescribe chloramphenicol ointment QDS for 5 days

Corneal ulcer:
  • Corneal defect extending down into the stroma. It may appear white, fluffy, irregular and apparent even without a slit lamp
  • Typical clinical features include: Pain, Watering, Photophobia
  • A staining epithelial defect with associated haziness (infiltrates)
  • Always consider corneal ulcer in contact lens wearers presenting with painful red eye
  • Discuss with ophthalmology prior to starting any treatment

Scleritis:
  • Vasculitis of the sclera involving generalised inflammation and oedema of the conjunctiva
  • Associated with connective tissue disorders (e.g rheumatoid arthritis) and infections (e.g TB).
  • Clinical features include: Photophobia, reduced visual acuity, watery discharge, unilateral deep pink/red conjunctival injection +/- Tender globe
  • Mild cases can be treated with oral NSAIDs, but most need either high dose steroids or antibiotics to treat
  • Discuss with ophthalmology prior to starting treatment

Anterior Uveitis
  • Intraocular inflammation involving the iris +/- ciliary body.
  • If untreated, it can cause permanent damage and loss of vision from the development of glaucoma, cataract or retinal oedema
  • Can be associated with systemic autoimmune conditions such as ankylosing spondylitis or rheumatoid arthritis
  • Clinical features include: photophobia (very common), pain, reduced visual acuity, watery discharge
  • Unilateral circumcorneal injection with a hazy cornea
  • Pupil shape may be distorted and a hypopyon can be seen
  • The mainstay of treatment is topical steroids by ophthalmology
  • Patients can be prescribed tropicamide 1% or cyclopentolate 1% eyedrops BD to alleviate photophobia/ciliary spasm, but warn them the vision in that eye will be blurred as a result

Acute angle-closure glaucoma (AACG):
  • Sudden, large increase in intraocular pressure can result in damage to the optic nerve and irreversible sight loss if not treated promptly
  • Typical clinical features include: Significant ocular pain, Haloes in vision, reduced visual acuity, photophobia, circumciliary conjunctival injection (unilateral), hazy cornea, mid-dilated unreactive pupil, abdominal pain and vomiting
  • The association is poorly understood but patients can be misdiagnosed as having gastroenteritis - beware the ‘acute abdomen’ with a painful red eye
  • Aim of initial treatment is the reduction of intraocular pressure with topical and systemic agents
  • Requires urgent referral to ophthalmology

Endophthalmitis:
  • Severe, sight-threatening intraocular inflammation
  • Most commonly a result of bacterial infection though can be fungal or sterile
  • Most frequently associated with intraocular procedures (surgery/injections) or following trauma, but can occur endogenously as well
  • Remember to specifically ask about previous surgery/injections
  • Clinical features include: Reduced visual acuity, severe pain, often out of proportion to ocular signs - though some can present with no pain, swelling of the eyelids and/or conjunctiva (chemosis), intense conjunctival injections & hypopyon
  • Treatment involves an injection of antibiotics into the eye, as well as topical and oral systemic treatment
  • Requires urgent referral to ophthalmology

Red eye without pain alert-info
Blepharitis:
  • Inflammation of the eyelid margin
  • Often misdiagnosed as conjunctivitis
  • Clinical features include: Dry, gritty uncomfortable eyes with reflex lacrimation; itchy eyelids; crusting to the base of the eyelashes; swelling of the eyelids & erythema to the lid margin
  • Blockage of the meibomian glands
  • Can be associated with rosacea
  • The mainstay of treatment is mechanical debridement and cleaning of the lid margins:
  • Hot compresses
  • Lid margin - massage & cleaning
  • Topical lubricants can be prescribed to help the dry eye symptoms

Conjunctivitis:
  • Infection of the conjunctiva - can be bacterial, viral or allergic
  • Bacterial conjunctivitis typically has more purulent discharge than viral or allergic conjunctivitis
  • Viral conjunctivitis is extremely contagious
  • Clinical features include: Discharge, Diffuse conjunctival injection (unilateral or bilateral), Swollen conjunctiva (chemosis)
    • Viral conjunctivitis can be associated with pre-auricular lymphadenopathy
  • Treatment depends on the underlying cause:
    • Bacterial - mainly treated with chloramphenicol QDS for 7 days (fusidic acid in pregnancy/chloramphenicol allergy). Chlamydial and gonococcal conjunctivitis require oral treatment of the underlying systemic condition.
    • Viral - hand hygiene and topical lubricants for comfort. Do not prescribe antibiotics
    • Allergic - topical +/- oral anti-histamines are the first line treatment

Subconjunctival haemorrhage:
  • A flat, bright red patch under the conjunctiva with sharply defined borders and normal conjunctiva surrounding it
  • Contained by the limbus, does not spread onto the cornea
  • May look alarming but reassure the patient that it will resolve spontaneously, albeit slowly
  • Causes may include:
    • Spontaneous occurrence
    • Intraocular injections
    • Eye rubbing
    • Concurrent anticoagulant treatment - consider checking INR /clotting
    • Hypertension - may need BP monitoring if recurrent
  • No treatment is required, can give topical lubricants for comfort

Episcleritis:
  • Sectoral area of subconjunctival injection (unilateral)
  • Often confused with scleritis
  • Episcleritis is uncomfortable rather than painful
  • Usually minimal watery and no discharge
  • Can be differentiated from scleritis in two ways:
    • Phenylephrine 2.5% eyedrops will cause blanching of episcleral, but not scleral, vessels
    • Episcleral vessels are superficial and therefore can be moved with a swab pressing gently on the conjunctiva, after application of topical anaesthesia
  • Treatment includes hot compresses, topical lubricants +/- oral NSAIDs
  • Usually self-limiting and does not require referral to ophthalmology unless atypical, not resolving or frequent recurrence

Dry eye:
  • Caused by reduced tear production or poor quality tear film
  • Can be primary (idiopathic), or secondary due to:
  • Blepharitis
  • Systemic conditions including Sjogren’s syndrome and rheumatoid arthritis
  • Clinical features include: Diffuse conjunctival injection (unilateral or bilateral), features of blepharitis, fluorescein staining of the cornea
  • Treatment consists of topical lubricants (maybe as often as every hour) and any underlying causes

This is by no means a complete list of differentials of the red eye but covers the most common presentations. If in doubt, always escalate and ask for advice.

Written by Dr Harpreet Kaur (FY2) 
Corrections & checked by Dr Arun Kirupakaran (ST1 in Ophthalmology) & Mr Sarju Athwal (Consultant Ophthalmologist)