Purpose: Nasolacrimal duct obstruction (NLDO) is believed to be a risk factor for microbial keratitis (MK). The primary objective of this study was to look at microbiological concordance between corneal scraping and lacrimal sac flora in patients with concurrent MK and NLDO. The secondary objective was to compare microbiological isolates from MK and NLDO, MK alone, NLDO alone, and healthy subjects. Methods: A prospective comparative study of 146 subjects with standard microbiological analyses was performed between February 2014 and October 2017. Results: Of the 146 subjects, 35 had concurrent MK and NLDO, 35 had MK, 41 had NLDO, and 35 were healthy subjects. Overall, mean age and sex distribution among groups were similar. In the MK and NLDO group, coagulase-negative staphylococci (CNS) were the most common isolates from the corneal scraping (n = 12/35, 34%) and lacrimal sac (n = 10/35, 29%) with 58% concordance. CNS were also the most common isolates from the NLDO group and healthy subjects, fungus being the most common isolate in the MK group. Anatomical success was achieved in 31 patients (89%) after dacryocystorhinostomy (DCR) in the MK and NLDO group. The difference between the number of patients who had successful DCR surgery but failure of medical therapy for MK (1/31) versus those who failed DCR and medical therapy for MK (3/4) was statistically significant (P = 0.002, Fisher exact test). Conclusions: CNS are the most common organisms in concurrent MK and NLDO (58% concordance), in patients with NLDO alone, and as commensals in healthy subjects. Persistence of NLDO may be responsible for a poorer outcome of MK in a concurrent setting.

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