Comparison of Endophthalmitis Rates Between Prefilled Syringes and Standard Vials in Aflibercept Intravitreal Injections: A Retrospective Study in Japan.

Background: Bacterial endophthalmitis is a rare but serious complication of intravitreal injections (IVIs). Prefilled syringes have been introduced to reduce contamination risk during drug preparation. However, whether they lower the incidence of bacterial endophthalmitis compared to vials remains unclear. Methods: This retrospective cohort study analyzed aflibercept IVIs performed at 17 clinical centers in Japan between 2015 and 2022. Patients aged ≥20 years who received aflibercept IVIs (vial or prefilled syringe) for age-related macular degeneration, diabetic macular edema, retinal vein occlusion, or myopic choroidal neovascularization were included. Bacterial endophthalmitis was diagnosed based on clinical signs (e.g., rapid vision loss, pain, hypopyon, vitreous opacity). Incidence rates were compared using Fisher's exact test. Results: Among 152,039 injections (43,684 prefilled syringes; 108,355 vials), 12 cases of bacterial endophthalmitis were identified (0.0046% vs. 0.0092%, p = 0.53). Poor visual outcomes were associated with Enterococcus faecalis, Streptococcus spp., and diabetes. Conclusions: Although incidence was lower in the prefilled syringe group, the difference was not statistically significant. Detecting a significant difference requires a larger sample. Further studies are needed to confirm the potential benefits of prefilled syringes in reducing endophthalmitis risk.