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David Muller, Pavel Kamaev, Marc Friedman, Evan Sherr, William Eddington; Accelerated UVA-RF Corneal Cross-linking through Pulsed UVA Illumination and Oxygen Rich Environments. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5281.
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To determine the effects of using pulsed UVA light and an atmosphere with high oxygen concentration during UVA-RF cross-linking.
Fresh whole porcine eyes were obtained <24 hours postmortem in saline on ice from Sioux-preme (Sioux City, IA). Eyes were brought to 37oC in a humidity chamber, epithelium was removed with a dull blade, and an intraocular pressure of 15mmHg was applied using a water column. Drops of 0.1% RF in 0.85% saline were applied in a humidity chamber for 20 minutes. Eyes in oxygen groups had 100% oxygen pumped into the chamber for the final 5 minutes of pre-soak. Eyes were then placed under a UVA light with an automated shutter system (Sutter Instrument, Novato, CA) and irradiated at 30mW/cm2 either with constant irradiance or pulsed at a rate of 1.5 seconds on, 1.5 seconds off either in the ambient atmosphere or in a chamber with 100% Oxygen concentration for a total UVA dose of 5.4J/cm2. The eyes were then placed under an Intralase femtosecond laser system (Abbot Medical Optics, Santa Ana, CA) and a central 9mm diameter 200um thick flap was cut from the anterior surface of the cornea. The corneal flaps were then attached to a biaxial extensometer (CellScale Biotester 5000, Waterloo, ON) using a 5mm wide attachment mechanism and stretched until either a maximum load of 5N was applied or the sample failed. Flaps were then removed and digested in papain. Papain solutions were placed in a fluorometer (Photon Technology Int., London, Ontario, Canada) and excited at 360nm. Fluorescence at 450nm was measured.
Mechanical analysis showed an increase in corneal stiffness and fluorometric analysis showed a higher response at 450nm for crosslinking performed in an oxygen rich environment. The result was the same for pulsed UVA. The combination of pulsed UVA and an oxygen rich environment produced the most corneal stiffening and the highest fluorometric response.
Both pulsing UVA and performing the UVA irradiation in an oxygen rich environment increased the amount of crosslinking achieved for the same energy dose. When combined they have an additive effect.
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