In Vivo Evaluation of Preoperative Topical Strategies in Reducing Conjunctival Microbial Load before Intravitreal Injections

Purpose: To evaluate in vivo efficacy of different topical strategies administered before intravitreal injections (IVIs) in reducing conjunctival microbial load compared with standard preoperative disinfection with 5% povidone-iodine (PI-5%). Methods: This prospective randomized comparative study was conducted between January and July 2025 at a tertiary referral ophthalmology center. Patients scheduled for IVIs were randomly assigned to 4 groups: 0.1% Polyquaternium-133, 0.6% povidone-iodine, 0.02% chlorhexidine digluconate, or no preoperative drops [control group (CG)]. Antiseptic eye drops were administered 3 times daily for 3 days before the procedure. Conjunctival swabs were collected at baseline (T0), on the day of injection before standard disinfection (T1), and 3 minutes after PI-5% application (T2). Microbial load was assessed by colony-forming unit (CFU) count, and microorganisms were identified. Results: A total of 205 patients were enrolled. In the CG, no significant difference was observed between T0 and T1, while PI-5% produced a significant CFU reduction at T2. Preoperative treatment with 0.6% povidone-iodine or 0.02% chlorhexidine digluconate did not significantly reduce CFU counts at T1. In contrast, 0.1% Polyquaternium-133 resulted in a significant reduction in bacterial load between T0 and T1, with a further decrease after PI-5%. Qualitative analysis showed selective effects of antiseptics on conjunctival microbial composition, with Polyquaternium-133 demonstrating marked activity against predominant species, including Corynebacterium macginleyi and Staphylococcus aureus . Conclusions: Complete conjunctival sterility was not achieved with any regimen. However, 0.1% Polyquaternium-133 significantly reduced conjunctival bacterial load and showed a complementary effect when combined with standard PI-5% disinfection, suggesting potential clinical benefit in prophylaxis.