What might suggest fungal infection in corneal ulcerations?

• A. Lack of response or decline with antibiotics suggests fungus
• B. Good cytology (scrape) +/- stains (rose bengal)
• C. Corneal biopsy (usually at surgery)
• D. Confocal microscopy (newer, more advanced technique)

Answer: (A)

When a corneal ulcer in a horse fails to improve or gets worse despite appropriate antibiotic treatment, fungal infection becomes a strong possibility. Bacterial ulcers often show some response to antibiotics, at least initially, whereas fungi may persist and continue to invade the cornea because they require antifungal therapy. This clinical cue guides you toward fungal-focused diagnostics, such as corneal scraping for cytology with fungal stains to look for hyphae, or culture to identify the organism. More invasive or adjunct methods, like corneal biopsy in stubborn cases or confocal microscopy to visualize fungal filaments in vivo, can help confirm the diagnosis, but the lack of response to antibiotics is the key practical indicator prompting further fungal workup.