The “red eye” is a common presenting symptom in primary care, spanning a spectrum of conditions from benign to sight-threatening emergencies. Knowing how to differentiate these conditions quickly is key to providing safe, effective care.
Red Eye Fast Facts
- What causes red eye? Inflammation in any part of the eye can lead to redness. Understanding where the inflammation originates will help you narrow the differential.
- When to worry? While most cases are benign, emergent causes—though rare—require immediate attention to prevent vision loss.
- Where to start? A systematic approach using the CARE mnemonic—Common, Atypical, Rare, Emergent—can help you categorize red eye cases and decide when to refer or manage in the clinic.
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Common
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These conditions are typically non-emergent and manageable in an ambulatory setting:
- Conjunctivitis
- Bacterial: Purulent discharge, often unilateral.
- Viral: Watery discharge associated with upper respiratory symptoms.
- Allergic: Itchy, watery eyes, often bilateral.
- Blepharitis: Eyelid inflammation with crusting, often chronic.
- Corneal Abrasion/Foreign Body: History of trauma or sensation of something in the eye.
- Subconjunctival Hemorrhage: Bright red scleral patch, painless, benign.
- Dry Eye Syndrome: Burning, foreign body sensation, often chronic.
- Episcleritis: Mild localized redness, typically self-limited.
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Atypical
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Occasionally, red eye can result from non-ocular causes:
- Cluster Headaches: Severe unilateral pain with associated conjunctival injection and lacrimation.
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Rare
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Emergent causes are also thankfully rare, so we will lump these causes with emergent.
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Emergent Causes of Red Eye
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These conditions are sight-threatening and require emergent (dial the phone right now!) ophthalmology referral:
- Acute Angle Closure Glaucoma: Sudden severe pain, headache, nausea, blurred vision, and a fixed, mid-dilated pupil.
- Keratitis
- Bacterial, viral, parasitic: Pain, photophobia, discharge, and corneal opacity or ulceration.
- Iritis/Anterior Uveitis: Photophobia, pain, and a constricted pupil.
- Scleritis: Deep, severe pain and redness that may involve the sclera and episcleral vessels.
- Chemical Burn: History of exposure; requires immediate irrigation and urgent referral.
- Hyperacute Bacterial Conjunctivitis: Often caused by N. gonorrhoeae; copious purulent discharge, rapid progression.
- Orbital Cellulitis: Eyelid swelling, redness, pain with eye movement, and possible proptosis.
- Hyphema: Blood in the anterior chamber, often from trauma.
- Hypopyon: Pus in the anterior chamber, usually from infection.
- Endophthalmitis: Infection inside the eye, often following surgery or trauma; presents with severe pain, decreased vision, and a red eye.
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Red eye is a frequent complaint in primary care, with differential diagnoses ranging from minor, self-limiting conditions to rare, sight-threatening emergencies. A systematic approach using the CARE mnemonic can help guide clinical decision-making. Most cases, such as conjunctivitis, dry eye syndrome, or corneal abrasions, are manageable in outpatient settings, while emergent conditions like acute angle-closure glaucoma, orbital cellulitis, or chemical burns require immediate referral to prevent vision loss. Key red flags to remember for emergent causes include severe pain, vision changes, photophobia, and unilateral redness with proptosis. By staying vigilant and methodical, you can ensure safe, effective care for patients presenting with red eye.