The rapid detection of Acanthamoeba in paraffin-embedded sections of corneal tissue with calcofluor white.

Acanthamoeba keratitis is a difficult diagnosis to make with routine stains and cultures. Gram's, Giemsa, and hematoxylin-eosin stains do not differentially stain Acanthamoeba, making the detection of organisms difficult. Trophozoite and cyst forms in paraffin-embedded corneal tissue sections can be rapidly and differentially stained with calcofluor white. Under the fluorescence microscope, the trophozoites are bright red-orange, and cyst cell walls fluoresce bright apple-green with red-orange cytoplasm. Retrospective identification can be made by destaining hematoxylin-eosin-stained sections. Digesting background corneal tissue with trypsin or collagenase and hyaluronidase solutions helps to more readily identify trophozoites.