How can you differentiate between types of conjunctivitis (pink eye)?

Differentiating Types of Conjunctivitis (Pink Eye)

The most reliable way to differentiate conjunctivitis types is by examining the discharge pattern (purulent/mucopurulent suggests bacterial, watery suggests viral or allergic), presence of itching (strongly indicates allergic), and associated symptoms (fever/pharyngitis suggests viral, seasonal pattern suggests allergic). 1, 2

Critical Red Flags Requiring Immediate Evaluation

Before attempting to differentiate routine conjunctivitis types, always rule out vision-threatening conditions first:

• Purulent discharge with corneal involvement - Gonococcal conjunctivitis can cause corneal perforation within 24-48 hours and requires immediate systemic antibiotics 3
• Any purulent conjunctivitis in a neonate - This is an emergency until gonococcal and chlamydial causes are ruled out, as gonococcal infection can lead to septicemia, meningitis, and death 3
• Severe pain with decreased vision - May indicate uveitis, acute angle-closure glaucoma, or scleritis rather than simple conjunctivitis 1, 2
• Vesicular rash on eyelids or nose - Suggests herpes simplex or varicella zoster virus, which can progress to keratitis, corneal scarring, and vision loss 3, 2
• Always examine the cornea with fluorescein staining in any purulent conjunctivitis to detect early corneal involvement 3

Primary Differentiation Algorithm

Step 1: Assess the Discharge Type

Bacterial Conjunctivitis:

• Mucopurulent or purulent discharge with eyelids matted shut upon waking is the hallmark of bacterial conjunctivitis 1, 2
• More common in children than adults 2
• Typically remains unilateral (though can become bilateral) 1
• Mattering and adherence of eyelids on waking, lack of itching, and absence of prior conjunctivitis history are strongest predictors 4

Viral Conjunctivitis:

• Watery to serofibrinous discharge characterizes viral conjunctivitis 3, 1, 2
• Often begins unilaterally but progresses to bilateral involvement within days 3, 1
• Most common overall cause of infectious conjunctivitis 4

Allergic Conjunctivitis:

• Watery discharge with minimal to no discharge in many cases 2
• Bilateral presentation from onset 1

Step 2: Evaluate for Itching

• Presence of itching is the strongest indicator of allergic conjunctivitis and essentially rules out bacterial causes 1, 4
• Absence of itching supports bacterial or viral etiology 4

Step 3: Look for Associated Symptoms and Signs

Viral Conjunctivitis Indicators:

• Fever, pharyngitis, and bilateral conjunctivitis form the diagnostic triad of pharyngoconjunctival fever (adenovirus) 3
• Periauricular or preauricular lymphadenopathy 3, 1
• Follicular reaction on inferior tarsal conjunctiva 3
• Recent sick contacts or household members with similar symptoms 3
• Self-limited course of 5-14 days 3, 1

Bacterial Conjunctivitis Indicators:

• Rapid onset over hours to 1-2 days 2
• Most uncomplicated cases resolve in 1-2 weeks even without treatment 4
• May have preauricular lymphadenopathy but less common than viral 1

Allergic Conjunctivitis Indicators:

• Seasonal pattern or exposure to known allergens 5
• Bilateral presentation with chemosis (conjunctival swelling) 1
• Papillary reaction on tarsal conjunctiva 1
• History of atopy, asthma, or allergic rhinitis 2

Step 4: Examine the Pattern of Redness

• Diffuse pattern of redness is common in all types of conjunctivitis 1
• Sectoral or localized redness suggests hyperemia from localized irritation rather than true conjunctivitis 1
• Perilimbal pattern may indicate more serious conditions like scleritis or uveitis requiring urgent referral 1

Special Populations and High-Risk Features

Contact Lens Wearers:

• Any conjunctivitis in contact lens wearers requires antibiotic treatment due to risk of Pseudomonas and other serious pathogens 4
• Consider bacterial keratitis, which is vision-threatening 1

Sexually Active Patients with Follicular Conjunctivitis:

• Follicles on bulbar conjunctiva and semilunar fold are distinctive for chlamydial conjunctivitis, requiring systemic antibiotics 3
• Consider sexual abuse in children with gonococcal or chlamydial conjunctivitis 3

Immunocompromised Patients:

• Higher risk for severe complications and atypical presentations 3
• Lower threshold for ophthalmology referral 2

Common Diagnostic Pitfalls

• No single sign or symptom accurately differentiates viral from bacterial conjunctivitis - use the combination of features described above 2, 6
• Overlooking serious conditions like uveitis, acute angle-closure glaucoma, or scleritis by assuming all red eyes are simple conjunctivitis 1
• Failing to perform fluorescein staining in purulent cases, missing early corneal involvement 3
• Missing adenoviral progression to epidemic keratoconjunctivitis with subepithelial infiltrates that can cause long-term visual sequelae 3

When to Refer to Ophthalmology

Immediate referral indicated for:

• Neonatal conjunctivitis 2
• Severe pain or decreased vision 2
• Recent ocular surgery 2
• Vesicular rash on eyelids or nose 2
• History of rheumatologic disease 2
• Immunocompromised state 2
• Prolonged symptoms beyond 10 days without improvement 7
• Chronic or recurrent red eye 7
• Evidence of corneal infiltration or hypopyon 7