International audiencePURPOSE: This study was designed to compare the diagnostic yield of microbiological analysis performed on diluted and undiluted vitreous samples from pars plana vitrectomy (PPV) in patients with acute postcataract endophthalmitis. DESIGN: Cohort study, evaluation of diagnostic test or technology. PARTICIPANTS: Patients with acute postcataract endophthalmitis (<6 weeks). METHODS: Undiluted and diluted vitreous samples were taken from 34 consecutive patients at the beginning of PPV as part of the multicenter prospective study of the French Institutional Endophthalmitis Study (FRIENDS) group. Vitrectomy was performed after 1 (n = 12) or 2 (n = 22) intravitreous antibiotic injections. McNemar's nonparametric test was used ...