The etiology of severe microbial keratitis includes bacteria (Pseudomonas aeruginosa, Streptococcus pneumonia, and Staphylococcus aureus), fungi, herpes keratitis, and Acanthamoeba. Risk factors include contact lens wear, trauma, postsurgical infection, foreign bodies, neurotrophic keratopathy, dry eyes, and eyelid abnormalities. Management must include history to determine risk of infection, cornea scraping and cultures, antimicrobial treatment (depends on underlying cause of infection), and follow-up.