Which staining methods are commonly used to visualize fungi in corneal scrapings?

• A. Calcofluor white stain and KOH preparation
• B. Gram stain and acid-fast stain
• C. Giemsa stain and Wright stain
• D. India ink stain

Answer: (A)

Detecting fungi in corneal scrapings relies on staining techniques that both highlight fungal cell walls and clear background material, making hyphae and yeasts visible. Calcofluor white binds to the polysaccharides in fungal cell walls (like chitin) and fluoresces under UV or blue light, so fungal elements appear bright against a dark background. This fluorescence increases sensitivity, allowing detection of fungal structures even when they’re few in number.

A potassium hydroxide (KOH) preparation digests keratin and other debris in the sample, further clarifying the slide so fungal elements stand out under ordinary light microscopy. The combination of clearing with KOH and staining with Calcofluor white is fast, inexpensive, and widely used in clinical practice to visualize fungi in corneal scrapings.

Other stains listed—Gram, acid-fast, Giemsa, Wright, or India ink—are not optimized for routine visualization of fungi in corneal scrapings or are better suited to other organisms or tissues, so they are less effective for this purpose.