Impact of Fluorescein on the Antimicrobial Efficacy of Photoactivated Riboflavin in Corneal Collagen Cross-linking

PURPOSE: To investigate the effect of fluorescein on the antimicrobial efficacy of photoactivated riboflavin in corneal collagen cross-linking (CXL) in vitro. METHODS: The ultraviolet light-A (UVA) absorption by fluorescein and riboflavin in different concentrations was analyzed with a spectrophotometer. The killing rate of Staphylococcus aureus strains after CXL with UV-A irradiation using different solutions containing riboflavin and/or fluorescein, was evaluated in vitro. RESULTS: Fluorescein absorbed UV-A to a significant extent, which augmented with increasing concentration. Moreover, addition of fluorescein to the riboflavin solution contributed to a significant reduction of the killing rate of S. aureus strains after 30 minutes of UV-A irradiation in vitro with a killing rate of 85%, whereas it was 47% in the presence of 2% fluorescein (P = .0247). CONCLUSIONS: The results indicate that fluorescein competes with riboflavin for the absorption of UV-A during CXL and reduces the antimicrobial effect of the procedure. The authors recommend that physicians treating infectious ulcerative keratitis by CXL should not stain the cornea with fluorescein for visualization of the corneal ulceration prior to CXL.