## Fungal vs. Bacterial Corneal Ulcers: Distinguishing Features **Key Point:** Satellite lesions with feathery or irregular borders are the most specific clinical sign of fungal corneal ulcer and help differentiate fungal from bacterial disease. ### Satellite Lesions in Fungal Keratitis **Definition:** Small, isolated infiltrates surrounding the main ulcer, separated by clear cornea. **Mechanism:** Fungal hyphae spread laterally and anteroposteriorly through corneal tissue, creating multiple foci of inflammation. **Appearance:** - Feathery, irregular, or serrated borders - Hyphal pattern visible with high magnification - Multifocal distribution (unlike bacterial ulcers) - May coalesce over time ### Comparison Table: Fungal vs. Bacterial Corneal Ulcers | Feature | Fungal | Bacterial | | --- | --- | --- | | **Onset** | Slow (days to weeks) | Rapid (24–48 hrs) | | **Borders** | Feathery, irregular | Sharp, well-demarcated | | **Satellite lesions** | **Common** | Rare | | **Hypopyon** | Small or absent | Large, prominent | | **Discharge** | Minimal, mucoid | Copious, purulent | | **Stromal necrosis** | Minimal initially | Extensive | | **Progression** | Indolent | Aggressive | **High-Yield:** The presence of **satellite lesions with feathery borders** should immediately raise suspicion for fungal keratitis and prompt: 1. Corneal scrapings for KOH mount and culture 2. Initiation of topical antifungal therapy (natamycin, voriconazole) 3. Avoidance of topical steroids (which worsen fungal disease) **Mnemonic: FFSS** — **F**ungal keratitis = **F**eathery borders, **S**atellite lesions, **S**low progression. **Clinical Pearl:** Fungal ulcers are often misdiagnosed as bacterial initially because they respond poorly to antibiotics. Any corneal ulcer that fails to improve on appropriate antibiotics within 48–72 hours should raise suspicion for fungal disease, even without visible satellite lesions. 
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