## Clinical Diagnosis: Fungal Corneal Ulcer **Key Point:** The combination of a thorn prick injury, rural setting, dry granular ulcer base, satellite lesions, and branching septate filaments on Gram stain is pathognomonic for fungal keratitis, most commonly caused by *Aspergillus fumigatus*. ### Distinguishing Features of Fungal vs. Bacterial Ulcers | Feature | Fungal | Bacterial | |---------|--------|----------| | **Onset** | Slower (5–14 days) | Rapid (24–48 hours) | | **Edges** | Raised, infiltrated, feathery | Sharply demarcated | | **Base** | Dry, granular, necrotic | Purulent, mucopurulent | | **Hypopyon** | Present but less pronounced | Marked, rapidly progressive | | **Satellite lesions** | Common | Rare | | **Morphology (Gram stain)** | Branching septate filaments | Cocci or rods | | **Risk factor** | Trauma (thorn, vegetative matter) | Contact lens, corneal abrasion | **High-Yield:** *Aspergillus fumigatus* is the most common fungal cause of corneal ulcer in India, particularly in agricultural settings. The organism is ubiquitous in soil and plant material. **Clinical Pearl:** Fungal ulcers often progress despite topical antibiotics, leading to diagnostic delay. A high index of suspicion in the setting of vegetative trauma and a dry, granular ulcer base should prompt immediate fungal culture and KOH mount. ### Mnemonic for Fungal Keratitis Risk Factors: **TRAUMA** - **T**horn prick or vegetative matter injury - **R**ural/agricultural occupation - **A**spergillus (most common fungus) - **U**nresponsive to antibiotics - **M**ycological confirmation (KOH, culture) - **A**ntifungal therapy required (natamycin, voriconazole) **Tip:** Always perform KOH mount (10% potassium hydroxide) and fungal culture in suspected fungal keratitis. Gram stain showing branching septate filaments (not visible in bacterial keratitis) is the key differentiator here. [cite:Khurana Comprehensive Ophthalmology Ch 4] 
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