Significance of the riboflavin film in corneal collagen crosslinking

PURPOSE: To evaluate the role of the preocular riboflavin film in ultraviolet-A (UVA) absorption in corneal collagen crosslinking (CXL). SETTING: Eye Laser Institute, Department of Ophthalmology, Martin-Luther-University, Halle, Germany. METHODS: The absorption of UVA light was measured in human donor and porcine postmortem corneas with and without riboflavin film using 3 solutions: standard dextran riboflavin, methylcellulose riboflavin, and hypoosmolar riboflavin sodium chloride without dextran. The breakup time of the solutions and their absorbance were also determined. RESULTS: After 30-minute instillation of riboflavin solution, the corneal absorption coefficient of the combined stroma riboflavin film system was 56.36 cm(-1) in human corneas and 51.46 cm(-1) in porcine corneas using dextran riboflavin; 69.87 cm(-1) and 53.86 cm(-1), respectively, using methylcellulose riboflavin; and 48.19 cm(-1) and 42.68 cm(-1), respectively, using hypoosmolar riboflavin. For the stroma alone without riboflavin film, the absorption coefficient was reduced to 36.95 cm(-1) in human corneas and 28.91 cm(-1) in porcine corneas using dextran riboflavin; 38.26 cm(-1) and 32.49 cm(-1), respectively, using methylcellulose riboflavin; and 38.88 cm(-1) and 28.42 cm(-1), respectively, using hypoosmolar riboflavin solution. The breakup time was 22 minutes for the dextran riboflavin film, 32 minutes for methylcellulose, and 90 seconds for the hypoosnnolar solution. CONCLUSION: Results indicate that the cornea including the riboflavin film can be considered a composite 2-compartment system and that the riboflavin film is an integral part of the CXL procedure and important in achieving the correct stromal and endothelial UVA irradiance.