Fungal Keratitis Diagnosis and Management

Clinical Features and Diagnostic Procedures

The American Academy of Ophthalmology recommends that the microbiological investigation should be directed against fungal pathogens, specifically filamentous fungi, as the clinical presentation of feathery, finger-like infiltration with indistinct elevated margins is pathognomonic for fungal keratitis 1, 2
Feathery, finger-like infiltration into adjacent corneal stroma is a characteristic finding that distinguishes fungal from bacterial keratitis, with a diagnostic accuracy of less than 70% based on clinical appearance alone 1, 2
The greyish-white appearance with stromal involvement and hypopyon formation is a common feature of fungal keratitis 2
Corneal scrapings should be performed with specific stains, including Calcofluor-KOH stain, which is most sensitive for fungal elements 3
Potassium hydroxide (KOH) preparation and Gram stain should also be performed to rule out bacterial co-infection 2, 3
Fungal culture should be performed using direct bedside inoculation of culture plates with corneal scraping material, with at least one culture plate or slant containing nonselective fungal growth medium 3

Confocal microscopy can be helpful for identifying fungal elements in vivo, particularly for filamentous fungi, with a high sensitivity and specificity 4, 5, 6
PCR testing may complement traditional methods for rapid specific identification, though it cannot distinguish between viable organisms and antigenic material 2
Delaying fungal-specific testing based solely on clinical appearance can lead to delayed diagnosis and treatment, and empiric corticosteroid use can worsen fungal keratitis outcomes 4, 5, 6, 7
Adequate sample collection from the leading edge of the infiltrate is crucial for optimal yield, and bacterial superinfection can occur 4, 5, 6

The most frequent filamentous fungi causing fungal keratitis include Fusarium species, Aspergillus species, and Dematiaceous fungi 3
Concurrent bacterial cultures should be obtained to rule out atypical organisms like Nocardia and Mycobacterial infections, which can produce similar feathery infiltrates 2, 4, 6