Abstract: Objective This study aimed to characterise the temporal changes in the conjunctival sac microbiota of both the operated and contralateral eyes following endoscopic dacryocystorhinostomy(EN-DCR), and to provide microbiological evidence to optimise the timing of subsequent intraocular procedures. Methods This study included 16 patients(32 eyes)who underwent EN-DCR at our institution. Bilateral conjunctival sac swabs were collected from each patient and processed for conventional bacterial culture. In addition, 16S rRNA gene sequencing was conducted on samples obtained from three randomly selected patients. Results In the operated eyes, the rate of positive bacterial cultures declined significantly from 10/16(62.5%)preoperatively to 2/16(12.5%)on postoperative day 2(P=0.001). The number of bacterial species decreased from 34 preoperatively to 20 on postoperative day 1 and to 2 on day 2, and remained sterile throughout the subsequent follow-up period. 16S rRNA gene sequencing revealed significant temporal changes in alpha diversity, as measured by the Pielou index(P=0.031), while β diversity remained statistically unchanged over time. Conclusions EN-DCR leads to a marked reduction in the bacterial evenness within the conjunctival sac of the operated eye, with negligible effect on the contralateral eye. The postoperative decrease in microbial load may mitigate the risk of infection and provides microbiological evidence to guide the timing of subsequent intraocular procedures.

Key words: Endoscopic dacryocystorhinostomy, Conjunctival sac microbiota, 16SrRNA sequencing