What are the differential diagnoses and initial treatment options for a patient presenting with eye redness and irritation?

Differential Diagnoses for Eye Redness with Irritation

When evaluating eye redness with irritation, systematically consider conjunctivitis (viral, bacterial, allergic), dry eye syndrome, blepharitis, keratitis, corneal abrasion, subconjunctival hemorrhage, episcleritis, scleritis, iritis/uveitis, and acute angle-closure glaucoma—with immediate ophthalmology referral required for vision loss, severe pain, corneal involvement, pupil distortion, or elevated intraocular pressure. 1, 2

Primary Differential Categories

Infectious Causes

• Viral conjunctivitis: Self-limited condition resolving in 10-14 days, does not respond to antibacterial agents, often bilateral with watery discharge and follicular response 1, 2
• Bacterial conjunctivitis: Characterized by mattering/crusting on waking, mucopurulent discharge, conjunctival injection; may be self-limited in mild cases 1, 2
• Bacterial keratitis: Presents with severe pain, photophobia, foreign body sensation, and stromal infiltrates distinguishing it from simple abrasion; requires immediate empiric broad-spectrum topical antibiotics before culture results 1, 2, 3
• Herpes simplex keratitis: Sight-threatening, typically unilateral presentation with dendritic corneal lesions 1, 2

Inflammatory/Immune-Mediated Causes

• Allergic conjunctivitis: Itching is the hallmark symptom strongly suggesting allergic etiology, often bilateral with watery discharge and chemosis 1, 2
• Blepharitis and meibomian gland dysfunction: Chronic eyelid margin inflammation causing secondary conjunctival injection, burning, crusting; treatment must address underlying eyelid problem rather than just conjunctival symptoms 1, 2
• Dry eye syndrome: Presents with irritation, burning, redness, mucus discharge, fluctuating vision; symptoms often disproportionate to clinical signs making diagnosis challenging 1, 2
• Episcleritis: Localized or diffuse redness, mild discomfort, self-limited 2, 4
• Scleritis: Deep, boring pain often radiating to face, vision-threatening requiring systemic workup 2, 4
• Iritis/Uveitis: Photophobia, ciliary flush, cells in anterior chamber, may have irregular pupil 2, 4

Mechanical/Traumatic Causes

• Corneal abrasion: Acute onset pain, foreign body sensation, tearing, history of trauma or contact lens wear 1, 4
• Foreign body: Unilateral presentation with localized irritation and visible foreign material 1, 4
• Subconjunctival hemorrhage: Bright red blood under conjunctiva, painless, no discharge 4, 5
• Contact lens-related complications: Giant papillary conjunctivitis, corneal hypoxia, or infectious keratitis in contact lens wearers 1

Other Important Causes

• Mucus fishing syndrome: Cyclical chronic condition with excessive mucus production from repetitive mechanical removal, associated with underlying dry eye or allergic conjunctivitis 1
• Chemical/ultraviolet injury: History of exposure, acute onset, may have corneal epithelial defects 1
• Medication-related: Topical medications, systemic anticholinergics, or dupilumab therapy causing ocular surface disorders 1

Critical Red Flags Requiring Emergency Ophthalmology Referral

Immediate consultation is mandatory for: 1, 6, 2, 4, 7

• Vision loss or acute visual changes
• Severe pain not relieved by topical anesthetics
• Corneal involvement (opacity, infiltrate, or ulceration detected by fluorescein staining)
• Mid-dilated, poorly reactive, or asymmetric pupil suggesting acute angle-closure glaucoma
• Traumatic eye injury or recent ocular surgery
• Copious purulent discharge
• Signs of herpes infection
• Elevated intraocular pressure
• Significant photophobia with decreased vision

Essential Diagnostic Approach

History Elements to Elicit

• Symptom characteristics: Duration, time course, unilateral vs bilateral, character of discharge (watery, mucopurulent, mucoid) 1
• Presence of itching strongly suggests allergic etiology 2
• Pain severity: Mild irritation vs severe boring pain helps differentiate benign from serious conditions 6, 7
• Visual changes: Blurred vision, halos, photophobia, or vision loss 1, 6
• Contact lens wear: Type, hygiene practices, wearing schedule 1
• Recent exposures: Infected individuals, trauma (mechanical, chemical, UV), allergens 1
• Systemic symptoms: Upper respiratory infection, genitourinary symptoms, skin lesions, fever 1
• Medical history: Atopy, asthma, eczema, autoimmune disease, immunosuppression 1
• Medications: Topical/systemic drugs, particularly anticholinergics, antihistamines, immunotherapy 1

Physical Examination Components

• Visual acuity testing is essential baseline for every patient 6, 2
• External examination: Periorbital skin (rosacea, eczema), eyelid position/closure, regional lymphadenopathy 1
• Pupil examination: Size, shape, reactivity, afferent pupillary defect 6, 2
• Slit-lamp biomicroscopy: Eyelid margins, conjunctiva (injection pattern, discharge, follicles, papillae), cornea, anterior chamber 1
• Fluorescein staining: Essential for detecting corneal epithelial defects, ulcers, or dendritic lesions 6, 2
• Intraocular pressure measurement: Especially if angle-closure suspected 1, 6, 2

Common Pitfalls to Avoid

• Never dismiss transient symptoms (intermittent blurred vision, halos) as benign—may represent warning episodes before acute angle-closure crisis 6
• Do not patch eyes with suspected infection or in contact lens wearers 2
• Avoid topical corticosteroids until organism identified in suspected infections, as they may worsen herpetic keratitis 1, 2
• Do not delay ophthalmology referral when diagnosis uncertain or red flags present 1, 2, 5
• Recognize dry eye syndrome as commonly misdiagnosed cause of chronic red eye unresponsive to antibiotic treatment 8
• Avoid indiscriminate antibiotic use—viral conjunctivitis will not respond and mild bacterial cases are often self-limited 2
• Do not overlook systemic associations: Sjögren syndrome in dry eye patients, Stevens-Johnson syndrome, graft-versus-host disease 1
• Unilateral presentation should raise suspicion for herpes simplex keratitis or other serious pathology requiring urgent evaluation 2

Initial Management Algorithm

For mild cases without red flags: 1, 2

• Viral conjunctivitis: Supportive care, cool compresses, preservative-free artificial tears 9
• Suspected bacterial conjunctivitis: Broad-spectrum topical antibiotic (e.g., gatifloxacin) 3
• Allergic conjunctivitis: Topical antihistamine/mast cell stabilizer (e.g., ketotifen), allergen avoidance 10
• Dry eye syndrome: Preservative-free ocular lubricants, identify/treat underlying causes 1, 9
• Blepharitis: Eyelid hygiene, warm compresses, treat meibomian gland dysfunction 1

Reassess within 48-72 hours—if worsening, not improving, or new symptoms develop, refer to ophthalmology 2, 9, 10