Fluorescein dye has been placed on the surface of the eye, and this is the appearance seen under fluorescent light. The dye is collecting at the top and bottom conjunctival margins The lesion seen here is a dendritic ulceration that appears in the corneal epithelium. Such a dendritic ulcer is characteristic for infection with herpes simplex virus. This is herpes keratitis. [Image contributed by Nick Mamalis, MD, University of Utah]

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