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Florence Hoogewoud, Olivier Richoz, Farhad Hafezi; Antimicrobial efficacy of riboflavin / UV-A collagen cross-linking at different fluences in vitro. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5290.
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Infectious corneal ulceration is a common cause of visual loss. The final outcome is influenced by early diagnosis and traditionally by intensive treatment with topical antibiotics. UV-A activated riboflavin (corneal collagen crosslinking (CXL) represents a new potential therapeutic approach. Its mechanism of action is closely linked to the abundant generation of free radicals. Generation of free radicals is an intensity- and time-dependent process. The studies performed so far have all used the standard protocol (3 mW/cm2 during 30 min) that had been established for progressive keratoconus. Our study investigates the antimicrobial efficacy of CXL using three different intensities and time regimen while maintaining the same total energy dose.
A porous polymer 300 μm thick, containing 96% of water, not toxic for the bacteria and not UV-absorbing was used as a support for the experiment. Two solutions of 106 bacteria, one of methicillin-resistant Staphylococcus aureus and one of Pseudomonas aeruginosa, combined with 0.1% Riboflavin solution were instilled in the polymer. Three different protocols of UV-irradiation (365nm) using the same energy (5.4 mJ) at different time and power settings were tested (3 mW/cm2 during 30 min; 9 mW/cm2 during 10 min; 18 mW/cm2 during 5 min). After irradiation, the solution was cultured on a blood agar plate and the CFU (colony forming units) were counted after 24h of incubation. Controls without riboflavin and with riboflavin but without irradiation were performed.
At the three different intensities, the number of bacteria was reduced by 2 log(10) scales compared with both control groups. No significant differences were detected between the three protocols.
The bactericidal rate was comparable in all three protocols tested suggesting that in clinical practice the time-sparing protocol (18 mW/cm2 during 5 min) should provide as good results as the standard protocol (3 mW/cm2 during 30 min). Clinical trials will have to confirm this hypothesis.
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