What is the differential diagnosis for eye redness in a general adult population?

Differential Diagnosis for Eye Redness

The differential diagnosis for eye redness in adults includes conjunctivitis (viral, bacterial, allergic), blepharitis, dry eye syndrome, keratitis, corneal abrasion/foreign body, subconjunctival hemorrhage, iritis/uveitis, acute angle-closure glaucoma, scleritis, and chemical injury. 1

Immediate Sight-Threatening Conditions Requiring Emergency Referral

These conditions demand recognition within 24 hours to prevent permanent vision loss:

• Acute angle-closure glaucoma: Severe eye pain, blurred vision, halos around lights, mid-dilated fixed pupil, and elevated intraocular pressure 1, 2
• Keratitis/corneal ulcer: Moderate to severe pain, photophobia, loss of corneal transparency, visible corneal infiltrate or opacity on fluorescein staining 3, 4, 1
• Iritis/anterior uveitis: Eye pain (more than irritation), photophobia, blurred vision, and ciliary flush 1, 2
• Scleritis: Severe boring eye pain radiating to face/head, worse at night, with deep episcleral vessel injection 1
• Corneal abrasion with significant epithelial defect: Identified by fluorescein staining showing epithelial loss 4, 1
• Chemical burn: History of chemical exposure requiring immediate copious irrigation 1
• Gonococcal conjunctivitis: Severe purulent discharge with risk of rapid corneal perforation 4, 1

Common Self-Limited Conditions Manageable in Primary Care

Viral Conjunctivitis

• Watery discharge, bilateral involvement (often sequential), preauricular lymphadenopathy, recent upper respiratory infection 3, 1
• Self-limited over 1-2 weeks; manage with artificial tears and cold compresses 4
• Critical pitfall: Adenoviral conjunctivitis is highly contagious—counsel patients on hand hygiene and avoiding close contact 3

Bacterial Conjunctivitis

• Purulent discharge, matting of eyelids upon awakening, unilateral or bilateral 3, 1
• Most cases self-resolve within 7-10 days without antibiotics 3, 4
• If treating, use broad-spectrum topical antibiotics and reassess in 3-4 days 4, 1
• Common pathogens: S. aureus, H. influenzae, S. pneumoniae, M. catarrhalis 3

Allergic Conjunctivitis

• Bilateral itching (hallmark symptom), watery discharge, chemosis, history of atopy 3, 1
• Manage with topical antihistamines/mast cell stabilizers and cold compresses 4

Blepharitis

• Bilateral lid margin inflammation, crusting, burning sensation, worse in morning 1
• Treat with lid hygiene (warm compresses, lid scrubs) 4, 1

Dry Eye Syndrome

• Burning, gritty sensation, paradoxical tearing, symptoms worse later in day or with prolonged visual tasks 3, 5
• Commonly misdiagnosed cause of chronic red eye unresponsive to antibiotics 5
• Manage with preservative-free artificial tears; severe cases require ophthalmology referral 3, 4

Subconjunctival Hemorrhage

• Bright red blood under conjunctiva, painless, no discharge, normal vision 1, 2
• Benign and self-resolving over 1-2 weeks; no treatment needed 1

Red Flags Mandating Urgent Ophthalmology Referral (Within 24 Hours)

Use the RAPID acronym to identify patients requiring emergency evaluation 3, 4:

• Redness plus:
• Acuity loss or worsening vision
• Pain (moderate to severe ocular pain, not just irritation)
• Intolerance of light (photophobia)
• Damaged cornea (visible opacity or positive fluorescein staining)

Additional urgent referral criteria:

• Pain not relieved by topical anesthetics 1
• History of herpes simplex virus eye disease (risk of recurrence with vision-threatening complications) 4, 1
• Recent ocular surgery or penetrating trauma 1
• Distorted or irregular pupil 1
• Immunocompromised status (risk of atypical/severe infections) 4
• Copious purulent discharge suggesting gonococcal infection 4, 1

Conditions Requiring Standard Ophthalmology Referral (Within 4 Weeks)

• Recurrent episodes of conjunctivitis suggesting underlying chronic condition 4
• Failure to respond to appropriate treatment after 3-4 days 4, 1
• Unilateral symptoms persisting beyond expected course (consider alternative diagnoses) 3, 4
• Suspected dry eye with systemic disease (Sjögren's syndrome carries 18.9% malignancy risk) 3, 5

Critical Clinical Pitfalls to Avoid

Never initiate topical corticosteroids before ophthalmology evaluation if red flags are present. Steroids worsen infectious keratitis (especially herpes simplex and fungal), prolong adenoviral infections, and can precipitate acute angle-closure glaucoma 4, 1

Do not assume bilateral symptoms always indicate benign disease. While viral/allergic conjunctivitis typically presents bilaterally, bilateral keratitis or uveitis can occur 3

Recognize that absence of pain does not exclude serious pathology. Chronic angle-closure glaucoma and some cases of keratitis may present with minimal pain 2

In children with purulent conjunctivitis, consider sexual abuse if gonorrhea or chlamydia is identified and report to appropriate authorities 4

Diagnostic Approach Algorithm

1. Assess visual acuity first: Any vision loss requires same-day ophthalmology evaluation 4, 2

2. Evaluate pain severity: Moderate to severe pain indicates keratitis, iritis, or glaucoma—refer urgently 3, 4, 1

3. Check for photophobia: Presence suggests corneal or intraocular inflammation beyond simple conjunctivitis 3, 4

4. Examine cornea: Loss of transparency or positive fluorescein staining requires urgent referral 3, 4, 1

5. Assess discharge pattern:

   • Watery = viral 1
   • Purulent = bacterial 1
   • Mucoid/stringy = allergic 1

6. Determine laterality: Unilateral symptoms lasting >24 hours warrant broader differential consideration 3, 4

7. If no red flags present and diagnosis is straightforward conjunctivitis or blepharitis: Initiate appropriate treatment and reassess in 3-4 days 4, 1