## Distinguishing Fungal from Bacterial Corneal Ulcers ### Key Morphological Feature **Key Point:** Feathery infiltrate margins with satellite lesions are pathognomonic for fungal corneal ulcers and reliably distinguish them from bacterial ulcers. ### Comparative Table | Feature | Bacterial Ulcer | Fungal Ulcer | | --- | --- | --- | | **Infiltrate margin** | Sharp, well-demarcated | Feathery, ill-defined | | **Satellite lesions** | Absent | Present (characteristic) | | **Hypopyon** | Common, early | Rare or absent | | **Corneal edema** | Minimal | Extensive, out of proportion | | **Vascularization** | Rapid (3–5 days) | Delayed or absent | | **Course** | Rapid (24–48 hrs) | Indolent, slow progression | | **Exudate character** | Purulent, thick | Minimal, dry | ### Pathophysiology of Feathery Margins 1. **Fungal hyphae spread centrifugally** along corneal lamellae with minimal inflammatory response. 2. **Satellite lesions** represent isolated foci of fungal invasion ahead of the main ulcer — a unique feature of fungal keratitis. 3. **Bacterial ulcers** show sharp margins because acute suppuration creates a demarcation zone; fungal invasion is slower and more diffuse. **High-Yield:** The presence of satellite lesions + feathery margins = fungal ulcer until proven otherwise. This combination is almost never seen in bacterial keratitis. **Clinical Pearl:** Fungal ulcers often appear deceptively mild clinically (minimal exudate, no hypopyon) but are histologically more destructive — the ulcer depth and extent are always greater than the surface appearance suggests. ### Why Other Features Are Not Discriminatory - **Hypopyon:** Present in 50% of bacterial ulcers but rare in fungal; however, absence of hypopyon does NOT exclude bacterial infection. - **Corneal scarring & neovascularization:** Both occur in both types; non-specific. - **Pain & photophobia:** Equally severe in both; pain is not discriminatory. 
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.