Scanning Electron Microscopy of Conjunctival Scraping: Our Experience in the Diagnosis of Infectious Keratitis with Negative Culture Tests.

65 consecutive patients with presumed microbial keratitis and negative culture tests for bacteria and fungi obtained by corneal curettage were evaluated. All patients had undergone local broad spectrum antibiotic therapy for at least 5 days with no clinical improvement. After 48-72 h of wash-out they underwent scraping of the superior tarsal conjunctiva for cytological examination of cellular morphology in Scanning Electron Microscopy (SEM). The presence of pathogenic microorganisms was detected with this method in 62 of these patients, towards which specific therapy was carried out. Clinical improvement and eradication of microorganisms previously detected by SEM examination were observed in all positive patients over a time between 10 and 49 days. In three patients, no microorganisms were detected, but the presence of inflammatory cells (eosinophils and mast cells) or dry eye findings. This method could be useful to detect the presence of non-isolated microorganisms at common culture tests. The resolution of the infectious keratitis and the eradication of the pathogens at the subsequent cytological examination of cellular morphology in Scanning Electron Microscopy support the validity of the proposed method.