Red Eye Differentials

Overview – Red Eye Differentials

The term “red eye” refers to ocular redness caused by dilation of conjunctival or episcleral vessels in response to inflammation, infection, trauma, or increased intraocular pressure. Although most cases are benign and self-limiting, red eye can also signal sight-threatening pathology. Distinguishing between common and emergent causes is a key clinical skill for final-year medical students and junior doctors.

History Taking in Red Eye

Key questions to ask:

  • History of trauma or exposure?
    • Welding, contact lens use, exposure to chemicals or dust
  • Laterality?
    • Bilateral: Conjunctivitis (usually viral or allergic)
    • Unilateral: More concerning – think uveitis, acute glaucoma
  • Discharge?
    • Watery: Suggests viral causes, uveitis, or corneal ulcer
    • Sticky: Suggests bacterial conjunctivitis
  • Pain severity?
    • Mild discomfort = conjunctivitis
    • Severe pain or photophobia = uveitis, glaucoma, ulcer
  • Blurred vision or haloes?
    • Indicates more serious pathology

Red Flags

  • Unilateral red eye
  • Severe pain or photophobia
  • Visual disturbance or haloes
  • Pupillary abnormalities
  • History of contact lens use

Causes of Red Eye

Foreign Body

  • Mechanism: Trauma from metal, wood, or dust particles
  • Findings: Visible foreign object, conjunctival injection, tearing
  • Treatment:
    • Removal (e.g. drill-burr under topical anaesthesia)
    • Topical antibiotics post-removal
Red eye - FOREIGN BODY
E van Herk, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons

Subconjunctival Haemorrhage

  • Cause: Rupture of small conjunctival vessels
  • Triggers: Coughing, vomiting, hypertension, anticoagulants
  • Findings: Bright red patch under the conjunctiva
  • Treatment: None required – self-resolves in 1–2 weeks
  • Important: Check BP and anticoagulant history
red eye - SUBCONJUNCTIVAL HAEMORRHAGE
James Heilman, MD, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

Conjunctivitis

  • Definition: Inflammation of the conjunctiva
  • Types:
    • Bacterial: Sticky, purulent discharge; common pathogens include Staph aureus, Strep spp.
    • Viral: Watery discharge, often with preauricular lymphadenopathy
    • Allergic: Itchy, watery eyes with conjunctival swelling
  • Treatment: Lubricants, antihistamines (allergic), topical antibiotics (bacterial)
CONJUNCTIVITIS
Tanalai at English Wikipedia, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons

Corneal Abrasion

  • Cause: Scratch from contact lens, fingernail, dust
  • Diagnosis: Fluorescein staining under cobalt blue light
  • Findings: Linear epithelial defect
  • Treatment: Lubricating or antibiotic drops
  • Prognosis: Most heal within 24 hours
red eye - corneal abrasion
CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

Corneal Ulcer

  • Urgency: Ophthalmological emergency
  • Viral Causes:
CORNEAL ULCERS
Imrankabirhossain, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Bacterial Causes:
    • Contact lens wearers at high risk
    • Pseudomonas and Neisseria are most aggressive
bacterial corneal ulcer
Yoanmb, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Treatment:
    • Intensive topical antibiotics (e.g. fluoroquinolones)
    • Antivirals for HSV
    • Refer urgently

Uveitis

  • Definition: Inflammation of the uveal tract (iris, ciliary body, choroid)
  • Symptoms:
    • Pain, photophobia, blurred vision
    • Watery eyes
    • Possible hypopyon (pus in anterior chamber)
  • Causes: Idiopathic, autoimmune (e.g. HLA-B27), infections
  • Treatment:
    • Steroid eye drops
    • Systemic immunosuppressants if recurrent
UVEITIS
1.EyeMD (Rakesh Ahuja, M.D.)., CC BY-SA 2.5 <https://creativecommons.org/licenses/by-sa/2.5>, via Wikimedia Commons
UVEITIS treatment algorithm
2.https://www.sciencedirect.com/science/article/abs/pii/S1521694206000386

Summary – Red Eye Differentials

Red eye can stem from a broad spectrum of pathologies — ranging from benign conjunctivitis to vision-threatening glaucoma or corneal ulceration. A focused history and examination, with attention to red flags like pain, photophobia, and visual disturbance, is essential. For related conditions, visit our Nervous System Overview page.

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