In vivo confocal microscopy for the detection of canine fungal keratitis and monitoring of therapeutic response

Objective: To describe in vivo corneal confocal microscopy of dogs during the clinical course of fungal keratitis and correlate findings with clinical evaluations and an ex vivo experimental canine fungal keratitis model.

Animals studied: Seven dogs with naturally acquired fungal keratitis and ex vivo canine corneas experimentally infected with clinical fungal isolates.

Procedures: Dogs with naturally acquired fungal keratitis were examined by in vivo laser scanning confocal microscopy. Initial confocal microscopic examinations were performed to assist in establishing the diagnosis of fungal keratitis. Serial confocal microscopic examinations were performed to guide antifungal chemotherapy. Confocal microscopy images of canine corneal fungal isolates were obtained by examination of experimentally infected ex vivo canine corneas to corroborate in vivo findings.

Results: Fungi cultured and detected by PCR from canine corneal samples included Candida albicans, Fusarium incarnatum-equiseti, Malassezia pachydermatis, and a Rhodotorula sp. Linear, branching, interlocking, hyperreflective structures were detected by confocal microscopy in dogs with filamentous fungal keratitis and round to oval hyperreflective structures were detected in dogs with yeast fungal keratitis. Antifungal chemotherapy was associated with a progressive reduction in the distribution and density of corneal fungal elements, alterations to fungal morphology, decreased leukocyte numbers, restoration of epithelial layers, and an increased number of visible keratocyte nuclei. No dogs had a recurrence of fungal keratitis following medication discontinuation. Confocal microscopic fungal morphologies were similar between in vivo and ex vivo examinations.

Conclusions: In vivo corneal confocal microscopy is a rapid method of diagnosing fungal keratitis in dogs and provides a noninvasive mechanism for monitoring therapeutic response.