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R. Roizenblatt, D. Chai, R. N. Gaster, M. Farid, S. Herekar, J. V. Jester; Comparison Study of Ultraviolet A Irradiance of 3mW/cm2 versus 9mW/cm2 With Riboflavin on Corneal Collagen Cross-Linking Efficacy in Rabbit Eyes. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4979.
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While corneal cross-linking (CXL) induced by ultraviolet A (UVA)-riboflavin increases the biomechanical strength of the cornea, the amount of energy and delivery time of light required to achieve the optimal CXL effect is still under investigation. This study evaluates the relative efficacy of a new algorithm for CXL using an ex vivo rabbit eye model.
The traditional method for CXL involves the delivery of 3mW/cm2 of UVA (370nm) over 30 minutes. This study compared the above method to the delivery of 9mW/cm2 of UVA over 10 minutes. Twenty fresh rabbit corneas were divided into four groups of 5 eyes each. All corneas had an 8mm diameter area of epithelium scraped off. Group 1 received no treatment and was used as a control. Group 2 received Riboflavin-5P 0.1% eye drops without UVA irradiation, Group 3 received Riboflavin-5P 0.1% eye drops followed by 30 minutes of 3mW/cm2 irradiation. Group 4 received Riboflavin-5P 0.1% eye drops followed by 10 minutes of 9mW/cm2 irradiation. Eyes in groups 2-4 received Riboflavin-5P eye drops every 2 minutes for 30 minutes prior and during UVA treatment. After CXL, rigidity tests were performed using a 250µm diameter cylindrical probe with a hemispherical tip, fixed to a force transducer with a resolution of 0.5µN. The transducer was attached to a micrometric manual actuator. The probe was manually driven so that the probe indented the center of the cornea perpendicularly. The signal from the transducer was converted to force and recorded using LabChart 6 (AD Instruments Inc, Colorado Springs, CO).
The rigidity of the cornea was quantified with the average amount of indenting force (AIF) at a designated indentation depth of 500µm. The AIF was 0.8mN (STD 0.4) for group 1 (control) and 0.62mN (STD 0.29) for group 2 (riboflavin-only). Groups 3 (CXL treatment of 3mW/cm2 for 30 minutes) and 4 (CXL treatment of 9mW/cm2 for 10 minutes) showed significant increase (p<0.05) in mechanical strength with AIF 1.96mN (STD 0.472) and 1.56mN (STD 0.182) respectively. There was no statistically significant difference between groups 3 and 4 (p = 0.136).
An algorithm using 9mW/cm2 for CXL for 10 minutes is as effective in increasing corneal rigidity as the traditional delivery of 3mW/cm2 UVA for 30 minutes in the rabbit model.
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