ObjectiveTo observe the differences in the positive rate of conjunctival sac microbial culture after different methods of preventing infection before intravitreal injection (IVI). MethodsA prospective case-control study. A total of 1 200 participants with fundus diseases who received IVI injection at Tianjin Medical University Eye Hospital from July 2021 to December 2023 were included. Patients were randomly divided into 6 groups according to eye spot with antibiotic solution 3, 1 and 0 days before IVI and local eye disinfection with povidone-iodine (PVI) 3 min and 30 s before IVI: the first 3 days of antibiotics+3 min PVI group, the first 1 day of antibiotics+3 min PVI group, the first 0 days of antibiotics+3 min PVI group, the first 3 days of antibiotics+30 s PVI group, the first 1 day of antibiotics+30 s PVI group, the first 0 days of antibiotics+30 s PVI group, there were 200 cases in each group. Microbial sampling and cultivation of conjunctival sac were conducted before IVI to compare the differences in positive rates among different groups. Multiple group comparisons were conducted using one-way analysis of variance. The comparison of count data is conducted using χ2 test. ResultsAmong the 1 200 patients, there were 566 males and 634 females. Age (62.59±13.44) years old. There were 397 cases of diabetes and 482 cases of hypertension. IVI frequency (2.35±2.34). 64 cases were positive for conjunctival sac culture before IVI. The age (F=1.468), sex composition ratio (χ2=2.876), diabetes (χ2=10.002), hypertension (χ2=6.019), times of IVI (χ2=4.507), and positive rate of conjunctival sac bacterial culture (χ2=6.272) of patients in each group had no statistical significance (P＞0.05). Using the duration of antibiotic application before IVI as a stratified factor, there was no statistically significant difference in the positive rate of conjunctival sac culture between groups with different durations of antibiotic application before IVI [χ2=0.414, P=0.52, combined odds ratio (OR)=0.819, 95% confidence interval (CI) 0.493-1.360]. Using the duration of PVI application as a stratified factor, there was no statistically significant difference in the positive rate of conjunctival sac culture between different PVI disinfection times [χ2=0.000, P=1.000, combined OR=1.00, 95%CI 0.503-1.988]. ConclusionsPre IVI treatment with 0.5% PVI for 30 s can inhibit the growth of microbial colonies in the conjunctival sac. The application of local antibiotic eye fluid in the anterior eye of IVI cannot reduce the positive rate of conjunctival sac bacteria.