Bacterial Conjunctivitis vs Allergic Conjunctivitis
Bacterial Conjunctivitis and Allergic Conjunctivitis are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.
Bacterial Conjunctivitis vs Allergic Conjunctivitis at a glance
- Bacterial Conjunctivitis: Acute purulent conjunctival infection — most often self-limited; topical antibiotics shorten course.
- Allergic Conjunctivitis: IgE-mediated bilateral ocular itching, redness, and watery discharge — frequently with allergic rhinitis.
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Side-by-side comparison
| Feature | Bacterial Conjunctivitis | Allergic Conjunctivitis |
|---|---|---|
| At a glance | Acute purulent conjunctival infection — most often self-limited; topical antibiotics shorten course. | IgE-mediated bilateral ocular itching, redness, and watery discharge — frequently with allergic rhinitis. |
| Classic presentation | Bilateral mucopurulent discharge with eyelids matted shut on awakening and normal vision in a school-age child.; Eye redness, often beginning unilateral and spreading to fellow eye in 1-2 days; Mucopurulent (yellow/green) discharge throughout the day; Eyelids matted/stuck shut on awakening; Foreign body or 'gritty' sensation; Minimal or… | Bilateral itching with chemosis and watery stringy discharge in an atopic patient.; BILATERAL itching — the hallmark; 'I want to rub my eyes constantly'; Watery or stringy mucoid discharge; Redness, burning, foreign body sensation; Eyelid swelling and chemosis; Concurrent nasal symptoms (sneezing, congestion) — allergic… |
| Workup / key labs | Most cases: clinical diagnosis; no testing needed; Gram stain and culture if: hyperacute presentation, contact lens wearer, severe disease, neonate, immunocompromised, treatment failure; NAAT for Chlamydia trachomatis and Neisseria gonorrhoeae in adults with suspected STI conjunctivitis or in neonatal conjunctivitis | Clinical diagnosis based on history and exam; Allergy testing (skin prick or specific IgE) if persistent or trigger unclear; Conjunctival scraping rarely needed — would show eosinophils |
| Imaging | Slit-lamp examination if any pain, photophobia, decreased vision, contact lens wear, or treatment failure — exclude keratitis or iritis; Fluorescein staining if corneal involvement suspected | Slit-lamp examination for chemosis, papillae, and corneal involvement; Fluorescein staining if corneal symptoms — exclude shield ulcer or punctate keratitis |
| First-line treatment | Most uncomplicated bacterial conjunctivitis is self-limited; topical antibiotics shorten course and reduce transmission; Topical ocular antibiotic — erythromycin ophthalmic ointment 0.5%, polymyxin B/trimethoprim drops, or moxifloxacin/ofloxacin drops × 5-7 days; Avoid topical aminoglycosides (gentamicin, tobramycin) as first line —… | Allergen avoidance — close windows during high pollen counts, wash hands and face after exposure, dust mite covers, pet dander measures; Cold compresses to reduce itching and swelling; Artificial tears (preservative-free preferred) to dilute and wash allergens; Topical ophthalmic antihistamine/mast cell stabilizer — olopatadine… |
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