How do you differentiate between blepharitis and preseptal cellulitis in a patient presenting with eyelid swelling, redness, and discharge?

Differentiating Blepharitis from Preseptal Cellulitis

The key distinction is that blepharitis is a chronic eyelid margin inflammation with characteristic findings like collarettes, scaling, and meibomian gland dysfunction, while preseptal cellulitis is an acute infectious process with diffuse eyelid swelling, erythema, and warmth that does NOT involve the eyelid margin primarily and preserves normal extraocular movements and vision. 1, 2

Critical Distinguishing Features

Blepharitis Presentation

• Chronic course with symptoms worsening in the morning, not acute onset 1
• Eyelid margin involvement is primary—look for vascularization, hyperemia, scaling, and crusting specifically at the lid margin 1
• Collarette formation at the base of eyelashes (pathognomonic for staphylococcal blepharitis) 1
• Bilateral presentation is typical, though can be asymmetric 1
• Discharge is foamy on the eyelid margin, not purulent 1
• No fever or systemic symptoms 1
• Extraocular movements and vision remain normal unless corneal complications develop 1, 2

Preseptal Cellulitis Presentation

• Acute onset of diffuse eyelid swelling and erythema 2, 3
• Eyelid skin involvement with warmth and tenderness, NOT primarily the lid margin 2, 3
• Can be unilateral or bilateral, often following trauma or upper respiratory infection 4, 2
• Extraocular movements and vision MUST be normal—if abnormal, this is orbital cellulitis requiring emergency management 2, 5
• May have fever or systemic symptoms, especially in severe cases 4
• Purulent discharge may be present if conjunctivitis coexists 6

Examination Algorithm

Step 1: Assess Onset and Chronicity

• Acute onset (hours to days) → consider preseptal cellulitis 2, 3
• Chronic or recurrent (weeks to months) → consider blepharitis 1

Step 2: Localize the Primary Pathology

• Eyelid margin with collarettes, scaling, crusting → blepharitis 1
• Diffuse eyelid skin with warmth, erythema, no margin-specific findings → preseptal cellulitis 2, 3

Step 3: Check Vision and Extraocular Movements

• Both normal → preseptal cellulitis or blepharitis remain possible 2, 5
• Abnormal → this is NOT simple blepharitis or preseptal cellulitis; consider orbital cellulitis (emergency) or severe blepharitis with corneal involvement 2, 5

Step 4: Slit-Lamp Examination (if available)

• Meibomian gland abnormalities, tear film debris, corneal staining → blepharitis 1
• Normal lid margin anatomy with skin inflammation only → preseptal cellulitis 2, 3

Critical Red Flags Requiring Urgent Evaluation

For Suspected Blepharitis

• Unilateral presentation with ulceration and focal lash loss → rule out sebaceous carcinoma immediately with biopsy 7, 8
• Conjunctival cicatricial changes → consider ocular mucous membrane pemphigoid or malignancy 1, 7
• Marked asymmetry and resistance to therapy → biopsy mandatory 1, 8

For Suspected Preseptal Cellulitis

• Any limitation of extraocular movements or vision changes → this is orbital cellulitis, not preseptal; requires emergency CT imaging and IV antibiotics 2, 5
• Severe pain on eye movement → orbital involvement 2
• Immunocompromised patient → higher risk of severe complications including toxic shock syndrome 4

Common Diagnostic Pitfalls

• Assuming all eyelid swelling with redness is "just blepharitis" when acute onset and diffuse skin involvement indicate preseptal cellulitis 2, 3
• Missing unilateral chronic blepharitis as sebaceous carcinoma—this error can be life-threatening 7, 8
• Failing to distinguish preseptal from orbital cellulitis—always check extraocular movements and vision 2, 5
• Treating chronic follicular conjunctivitis as viral when it may be chlamydial, which can present with preseptal swelling 6

Management Implications

If Blepharitis

• Initiate eyelid hygiene with warm compresses and lid scrubs 8
• Topical antibiotic ointment for anterior blepharitis 1, 8
• Explain chronic nature requiring long-term compliance 1
• Re-evaluate in 2-4 weeks—if no improvement, consider biopsy 8

If Preseptal Cellulitis

• Oral broad-spectrum antibiotics covering Staphylococcus and Streptococcus 4, 3
• Re-evaluate in 24-48 hours to ensure no progression to orbital cellulitis 2, 3
• Consider imaging if clinical course is atypical or worsening 5