In vivo corneal confocal microscopy allows direct observation of microbiological features in infectious keratitis

Purpose To differentiate microbiological features of infectious keratitis in corneal epithelium. Methods We performed in vivo confocal microscopy (HRT III, Rostock Cornea Module) in 190 patients with diagnosed infectious keratitis of various etiology ‐ 72 viral, 66 bacterial, 34 fungal (fibrillar and candidal) and 18 amoebal keratitis. For corneal scans we used 400x lens and 63x magnification. Microscopic analysis of epithelial layer was performed to distinguish structures of epithelial cells morphology, inflammatory cells and potential microbes. Results In viral keratitis, due to size of viral particles, highly specific secondary changes within epithelial cells were observed in form of “owl eyes”– an equivalent of active virus replication in cells. In bacterial keratitis we observed structures of bacteria forming streptococcal configuration (diagnosed bacteriologically as Streptococcus pneumoniae and Enterococcus spp.), granular bacteria could not be easily distinguished because of similarity with leukocytes infiltration (diagnosed bacteriologically as Staphylococci). In fungal keratitis we detected fungi fibrilles (diagnosed mycologically as Fusarium spp.) as well as granular fungi – Candida spp. Amoebal keratitis presented presence of Acantamoeba cysts and trophozoits. Conclusion In vivo analysis of corneal epithelial histology shows high specificity and sensitivity in infectious keratitis diagnosis. Except describing corneal structure and inflammatory cells, it makes possible to distinguish microbiological features of keratitis.