A 58-year-old diabetic woman from Delhi presents with a 10-day history of progressive left eye pain and blurred vision. Examination reveals a 3 mm corneal ulcer with feathery, raised borders, satellite lesions, and a stromal haze. KOH mount of corneal scrapings shows septate hyphae. What is the most appropriate next step in management?

Explanation

## Clinical Context This patient has a **fungal corneal ulcer** (septate hyphae on KOH mount) with classic features: feathery borders, satellite lesions, stromal haze, and a history of diabetes (immunocompromised state). Fungal ulcers progress rapidly and require aggressive systemic and topical antifungal therapy. ## Fungal Corneal Ulcer: Diagnosis & Management ```mermaid flowchart TD A[Corneal ulcer + risk factors]:::outcome --> B{Clinical clues?}:::decision B -->|Feathery borders, satellites, stromal haze| C[Suspect fungal]:::urgent C --> D[KOH mount, culture on SDA]:::action D --> E{Septate or non-septate?}:::decision E -->|Septate hyphae| F[Filamentous fungus]:::outcome E -->|Yeast| G[Candida species]:::outcome F --> H[Natamycin 5% topical]:::action G --> I[Fluconazole or voriconazole]:::action H --> J[Oral itraconazole 200 mg BD]:::action I --> K[Oral fluconazole 400 mg daily]:::action J --> L[Refer to tertiary centre]:::action K --> L L --> M[Monitor closely, consider debridement if needed]:::action ``` ## Key Point: **Natamycin 5% is the topical agent of choice for filamentous fungal keratitis.** It is the only FDA-approved topical antifungal for corneal ulcers and achieves superior corneal penetration compared to azoles. ## High-Yield: | Feature | Filamentous Fungus | Candida | |---------|-------------------|---------| | **Hyphae** | Septate (e.g., *Aspergillus*, *Fusarium*) | Yeast or pseudohyphae | | **Topical agent** | Natamycin 5% (hourly) | Fluconazole 1% or voriconazole 1% | | **Systemic agent** | Itraconazole 200 mg BD | Fluconazole 400 mg daily | | **Borders** | Feathery, raised, satellite lesions | Diffuse, less demarcated | | **Stromal involvement** | Deep, with haze | Variable | **Mnemonic: NATAMYCIN for Filamentous — NAT = Non-Azole Topical** ## Clinical Pearl: Fungal ulcers in **diabetics** progress rapidly and have a poor prognosis if not treated aggressively. The combination of topical natamycin + systemic itraconazole (which achieves aqueous penetration) is standard. Referral to a tertiary centre is mandatory because: 1. Fungal ulcers often require corneal debridement or therapeutic keratoplasty 2. Risk of perforation is high 3. Requires specialist monitoring and potential surgical intervention ## Warning: ~~Fluconazole or voriconazole alone (topical) is inadequate for filamentous fungal keratitis.~~ While these azoles are effective against *Candida*, they have poor corneal penetration and are NOT first-line for *Aspergillus* or *Fusarium*. Natamycin is superior for filamentous fungi. ~~Corneal debridement as first-line is controversial~~ and should be deferred unless there is impending perforation or after initiation of antifungal therapy. Aggressive debridement may worsen the ulcer. ## Tip: - **Septate hyphae on KOH** = filamentous fungus → natamycin - **Yeast or pseudohyphae** = *Candida* → azole (fluconazole or voriconazole) - Always culture on **Sabouraud dextrose agar (SDA)** for fungal identification and antifungal susceptibility - Systemic antifungal is essential for stromal involvement - Tertiary referral is non-negotiable for fungal keratitis