Microbial keratitis is a severe and often blindness-inducing pathology which represents today the first reason for long-term hospitalization (more than 5 days) in ophthalmology. Its diagnosis is clinical and leads to an immediate hospitalization in the presence of serious criteria (Mackie classification). The entire process of microbiological diagnosis requires several days before etiological confirmation and therefore delays the initiation of targeted therapy. Recently, new PCR systems allowing the detection of 18 to 27 pathogens in 75 minutes have been developed. Their use could thus be transposed to ophthalmology by adapting the microbiological diagnostic technique to samples currently taken by swabbing the cornea. The investigators will compare their diagnosis performance versus conventional methods on patients who suffered for a microbial keratitis with severity criteria.