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Sarah Peterson, Pavel Kamaev, William A Eddington, Marc D Friedman, David Muller; The Role of Iron II (Fe+2) as a Cross-linking Enhancer in CXL. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1101.
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© ARVO (1962-2015); The Authors (2016-present)
Riboflavin (Rf) is used as a primary photosensitizer for Corneal Collagen Cross-linking (CXL). Understanding the underlying photochemical mechanisms provides insight into the addition of additives for enhancement of cross-linking efficiency. H2O2 is a byproduct of the Type I reaction in CXL. We investigated the addition of transitional metals such as Fe+2 to drive H2O2 to OH· through a Fenton-like reaction in a porcine eye model.
Fresh whole globe porcine eyes were obtained <24 hours postmortem in saline on ice from Sioux-preme (Sioux City, IA). Eyes were cleaned and de-epithelialized with a dull blade, then soaked for 20 minutes in an incubator set at 37°C by using a rubber ring to hold solutions (A) 0.1% Rf in distilled water or (B) 0.1% Rf with 0.5mM Iron(II) sulfate heptahydrate (Sigma Aldrich) in distilled water on the corneal surface. Eyes were placed in a beaker with a light oxygen stream for 2 minutes, and pan-corneally irradiated for 8 minutes at 30mW/cm2 pulsed 1 second on: 1 second off, measured with a power meter (Ophir, Inc.) at the corneal surface. Cross sections of cornea were first measured using biaxial extensiometry (Eddington W, et al. IOVS 2013;54:ARVO E-Abstract 1619), then analyzed using papain digestion (Rood-Ojalvo S, et al. IOVS 2013;54:ARVO E-Abstract 5280).
The results of extensiometry show Rf + Fe+2 obtained markedly increased stiffness over Rf alone. This was corroborated by the increase of fluorescence in corneal flaps digested with papain by approximately 45% compared to Rf alone.
The addition of Fe+2 to Rf increases the efficiency of corneal collagen cross-linking in a porcine eye model. The presence of iron catalyzes the formation of highly reactive OH· radicals from H2O2. This makes more OH· radicals available to further increase collagen crosslinking per equivalent UV dose. Fe+2may be used as an enhancer in riboflavin CXL.
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