A 38-year-old female gardener from Tamil Nadu presents with a 3-week history of progressive left eye pain, blurred vision, and a white corneal infiltrate. She reports a scratch from a plant leaf 4 weeks ago. On slit-lamp examination, there is a central corneal ulcer with feathery, branching edges and satellite lesions. KOH mount of corneal scraping shows septate hyphae. What is the most appropriate next step in management?

Explanation

## Diagnosis: Fungal Corneal Ulcer (Filamentous Fungus) ### Clinical Presentation **Key Point:** The combination of **vegetative trauma** (plant leaf scratch), **feathery branching edges**, **satellite lesions**, and **septate hyphae on KOH mount** is diagnostic of a filamentous fungal keratitis, most likely *Aspergillus* or *Fusarium* species. ### Microbiological Identification | Feature | Filamentous Fungi | Candida | Yeast | |---------|-------------------|---------|-------| | KOH mount | Septate hyphae with acute angle branching | Pseudohyphae + budding yeast | Budding yeast only | | Growth rate | Slow (days to weeks) | Moderate | Moderate | | Corneal presentation | Feathery, branching edges; satellites | Granular, raised ulcer | Superficial infiltrate | | Risk factor | Vegetative trauma | Contact lens; immunosuppression | Immunocompromised | ### High-Yield: Fungal Keratitis Classification **Mnemonic: ACFN** — *Aspergillus, Candida, Fusarium, Nocardia* - **Filamentous fungi** (septate hyphae): *Aspergillus*, *Fusarium*, *Scedosporium* - **Yeast** (budding cells): *Candida*, *Cryptococcus* - **Dimorphic**: *Histoplasma*, *Blastomyces* ### Treatment Algorithm for Filamentous Fungal Keratitis ```mermaid flowchart TD A[Fungal keratitis suspected]:::outcome --> B{Organism identified?}:::decision B -->|Filamentous fungi| C[Natamycin 5% first-line]:::action B -->|Candida/Yeast| D[Fluconazole or voriconazole]:::action C --> E[Hourly topical application]:::action E --> F[Add systemic itraconazole]:::action F --> G[Consider corneal scraping/culture]:::action G --> H[Monitor for perforation risk]:::urgent H --> I[Surgical intervention if needed]:::action ``` ### Pharmacotherapy for Filamentous Fungal Keratitis **Key Point:** **Natamycin 5%** is the GOLD STANDARD topical antifungal for filamentous fungi (Aspergillus, Fusarium). | Drug | Spectrum | Dosing | Corneal Penetration | Notes | |------|----------|--------|-------------------|-------| | **Natamycin 5%** | Filamentous fungi (Aspergillus, Fusarium) | Hourly while awake | Poor (topical only) | **First-line for filamentous fungi** | | Amphotericin B 0.15% | Broad (fungi, Candida) | 4–6 hourly | Moderate | Toxic; reserved for resistant cases | | Fluconazole | Candida, yeast | Topical 0.2% + systemic | Good | Better for Candida | | Itraconazole | Aspergillus, Fusarium | Systemic only | Moderate | Adjunctive to topical therapy | | Voriconazole | Aspergillus, Fusarium | Topical 1% + systemic | Excellent | Emerging option; expensive | ### Clinical Pearl **High-Yield:** Natamycin is a **polyene macrolide** that disrupts fungal cell membrane ergosterol. It has **poor systemic absorption**, so topical application is essential. Systemic **itraconazole** is added for deep stromal involvement and to reduce recurrence risk. ### Why Natamycin + Itraconazole? 1. **Natamycin 5%** — topical, high corneal concentration, fungicidal 2. **Itraconazole** — systemic, penetrates deep stroma, prevents recurrence 3. **Synergistic effect** — topical + systemic coverage ### Management Pearls **Warning:** Do NOT use topical corticosteroids in fungal keratitis — they promote deeper invasion and perforation. **Clinical Pearl:** Fungal keratitis progresses slowly but relentlessly. Perforation risk increases after 3–4 weeks. Consider **therapeutic keratoplasty** if ulcer approaches Descemet's membrane or shows signs of impending perforation. ### Prognosis With early diagnosis and appropriate therapy, visual outcomes are variable. Scarring and neovascularization are common sequelae.