Tandem scanning confocal corneal microscopy in the diagnosis of suspected Acanthamoeba keratitis

Objective: To evaluate the role of in vivo corneal tandem scanning confocal microscopy (TSCM) in the definitive diagnosis of suspected Acanthamoeba keratitis (AK). Design: Noncomparative interventional single-institution case series. Method. A retrospective case review of patients consecutively referred with suspected AK and undergoing corneal TSCM was performed. Results: A total of 63 cases that met the inclusion criteria for the study were referred for diagnostic evaluation. Tandem scanning confocal microscopy demonstrated Acanthamoeba cysts/trophozoites in 54 cases and fungal hyphae in 2, whereas 1 case was positive for both Acanthamoeba and fungus. Culture of the cornea or contact lenses was carried out in 35 cases, 9 of which were positive for Acanthamoeba. Six of the TSCM-positive cases also underwent corneal biopsy, being positive for Acanthamoeba in only 2. Six patients were negative for Acanthamoeba on TSCM, the etiology being fungal in 1 case, as shown by subsequent culture. One patient was positive on culture for Acanthamoeba but falsely negative by TSCM, which was limited by poor cooperation during the examination. Two cases initially masqueraded as Acanthamoeba keratitis but showed fungus on TSCM. Mean follow-up was 14 months. Conclusion: In vivo corneal TSCM can establish the diagnosis of Acanthamoeba keratitis rapidly and noninvasively, particularly when conventional microbiology is inconclusive.