Confirmation of confocal microscopy diagnosis of Acanthamoeba keratitis using polymerase chain reaction analysis

Background: Acanthamoeba keratitis has commonly been identified with in vivo confocal microscopy and confirmed with histologic examination of an epithelial biopsy specimen. Objective: To determine if Acanthamoeba keratitis can be verified using polymerase chain reaction (PCR) of epithelial biopsy specimens. Methods: Epithelial specimens from patients with suspected Acanthamoeba keratitis by confocal microscopy were tested for Acanthamoeba with PCR of Acanthamoeba ribosomal DNA. Results: Twenty-four of 31 patients with evidence of Acanthamoeba keratitis were positive for Acanthamoeba on PCR analysis using 3 sets of primers. In 22 cases, the sequence obtained closely matched Acanthamoeba castellanii. Conclusions: This study demonstrates that PCR analysis of epithelial biopsy specimens can provide definitive verification of the confocal microscopic and histologic identification of Acanthamoeba organisms associated with keratitis. Acanthamoeba keratitis is probably quite common, especially in contact lens wearers, although more than half of the patients in this study did not wear contact lenses.