Impression Cytology in Eyes with Clinical and Confocal Scan Features of Acanthamoeba Keratitis

PURPOSE To report impression cytology findings in specimens obtained from eyes with clinical and confocal microscopic features of Acanthamoeba keratitis (AK). METHODS In this interventional case series, impression cytology was obtained from corneas of patients with clinical and confocal microscopic features indicative of AK. Specimens were stained with Periodic acid-Schiff/Papanicolaou (PAS/PAP) and examined for the presence of PAS-reactive Acanthamoeba cysts and/or hyperchromatic pear-shaped trophozoites. All specimens were then decolorized and re-stained with calcofluor white (CFW) for the presence of chemofluorescent cysts. RESULTS Fifty-six eyes of 50 patients with mean age of 25.5±9.3 (range, 17 to 78) years were evaluated. Forty-one (82%) cases were female and 51 (91.1%) eyes had history of contact lens wear. PAS-reactive Acanthamoeba cysts and/or hyperchromatic pear-shaped trophozoites were identified in 53 eyes (94.6%), 2 of which demonstrated only trophozoite- like structures. CFW staining was able to reveal the presence of chemofluorescent cysts in all 51 specimens (91.1%) in which cysts had been demonstrated with PAS/PAP staining. Trophozoites were not detected with CFW due to background staining of the cellulose acetate strip used for impression cytology. CONCLUSION Corneal impression cytology, stained with PAS/PAP or with CFW, successfully detects Acanthamoeba and can be employed for early noninvasive diagnosis of AK.