PURPOSE.To model the photochemical kinetics of corneal crosslinking 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, deepithelialized 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. (Invest Ophthalmol Vis Sci.
Background and Objective: Multi-pass treatments with pulse dye lasers (PDLs) are avoided due to perceived side effects. Proper multi-pass techniques allow for deeper vascular injury. New extended PDLs allow use of multipass procedures. This study evaluates how the time between pulses, inter-pulse interval [IPI] affect extent of vascular treatment. Study Design/Materials and Methods: Sixteen subjects were exposed to a series of exposures on normal skin to determine depth of injury for various IPI. Subjects were exposed to single pass, and 4 double-pass intervals. Tests included exposures at 0.5 milliseconds, 2-7 j/cm 2 . Exposures included one and two passes, IPI of 1, 10, 30, and 60 seconds; 5 and 30 minutes. Treatments were done with PhotoGenica V-Star (595-nm), SmartCool air cooling. Biopsies were taken: single pass and double pass purpuric thresholds; and at 7 j/cm 2 to determine depth of vascular coagulation. Results: Histology revealed increased vascular coagulation depth at purpura threshold for intervals of 1, 10, 30, and 60 seconds between passes compared to single pass treatment, and a significant monotonic increase in depth of vascular injury at 7 j/cm 2 with increasing IPI. Conclusions: The use of multiple passes increases depth of vascular injury, which may increase the efficacy of treatment without significant increase in purpura or risk of scarring for treatments at purpura threshold. At purpura threshold, the depth of vascular injury increases with increasing IPI up to 60 seconds. Above purpura threshold, there is a monotonic increase in depth of vascular injury for IPI up to 30 minutes. These observations suggest multipass treatment methods may be beneficial when employed with PDLs.
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