title: Photochemical kinetics of corneal cross-linking with riboflavin.
abstract: OBJECTIVE
  To model the photochemical kinetics of corneal cross-linking with riboflavin (Rf) and confirm the model through measured oxygen concentration experiments under varying energy input conditions by UV-A irradiance and temperature modulation in ex vivo porcine cornea.
  
  
  METHODS
  A theoretical model was developed to describe the corneal cross-linking photochemical kinetics of Rf. After instillation with drops of Rf solution in distilled water, de-epithelialized porcine corneas were exposed to 365-nm ultraviolet light (UV-A) under varying irradiance and temperature. Oxygen concentration in the cornea at a known depth was monitored during UV-A illumination with a dissolved oxygen fiberoptic microsensor. Data from the oxygen experiments were used to confirm the model.
  
  
  RESULTS
  On the basis of the known chemical reactions and diffusion rates of Rf and oxygen into the cornea, the authors developed a theoretical model consistent with corneal oxygen consumption experimental results during UV-A irradiation under different conditions. Oxygen concentration in the cornea is modulated by UV-A irradiance and temperature and quickly decreased at the beginning of UV-A exposure. The time-dependence of both Type-I and Type-II photochemical mechanisms in corneal cross-linking with Rf are discussed.
  
  
  CONCLUSIONS
  Using a chemical kinetics modeling approach, the authors developed a simple model that is in agreement with their experimental results on oxygen consumption in the cornea during corneal cross-linking with Rf. It is suggested that the main photochemical kinetics mechanism is the direct interaction between Rf triplets and reactive groups of corneal proteins, which leads to the cross-linking of the proteins mainly through radical reactions.
authors.affiliation: Avedro, Waltham, Massachusetts 02451, USA.
authors.forename: Pavel
authors.initials: P
authors.lastname: Kamaev
authors.forename: Marc D
authors.initials: MD
authors.lastname: Friedman
authors.forename: Evan
authors.initials: E
authors.lastname: Sherr
authors.forename: David
authors.initials: D
authors.lastname: Muller
mesh_terms: D000818:Animals; D003315:Cornea / Q000378:metabolism*; D003432:Cross-Linking Reagents / Q000493:pharmacokinetics*; D010100:Oxygen / Q000378:metabolism* / Q000528:radiation effects; D017319:Photosensitizing Agents / Q000493:pharmacokinetics*; D012256:Riboflavin / Q000493:pharmacokinetics*; D013552:Swine; D013696:Temperature; D014466:Ultraviolet Rays
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D010100:Oxygen; D012256:Riboflavin