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William Eddington, Marc Friedman, Evan Sherr, David Muller; Biaxial Biomechanical Study of UVA-RF Corneal Cross-linking. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1619. doi: https://doi.org/.
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To evaluate a method of biaxial extensometry applied to corneal flaps created with a femtosecond laser system for determining changes induced by various UVA-RF based corneal cross-linking protocols.
Fresh whole porcine globes were obtained <24 hours postmortem in saline on ice from Sioux-preme (Sioux City, IA). Eyes were brought to 37oC, epithelium was removed with a dull blade, intraocular pressure of 15mmHg was applied using a water column, and corneal thickness readings were recorded using an ultrasonic pachymeter (DGH Technology, Exton, PA) Eyes were separated into three groups containing 7 eyes each. Eyes were then soaked in a solution consisting of 0.1%RF and 0.85% saline for 20 minutes. One group was set aside (Control) and the other two groups were placed under UVA light at 365nm with an irradiance of 3mW/cm2 for a total UVA dose of 5.4J/cm2 and 2.7J/cm2 for groups 2 and 3 respectively. The eyes were then placed under an Intralase femtosecond laser system (Abbot Medical Optics, Santa Ana, CA) and 200um thick corneal flaps were cut from the anterior center of the cornea. Corneal flaps were removed and attached to a biaxial extensometer (CellScale Biotester 5000, Waterloo, ON) using a 5mm wide attachment mechanism (Figure 1) and submerged in a 37oC saline bath. Flaps were stretched from a relaxed state at a rate of 4um/s until a load of 5N or sample failure was reached.
Stress strain curves can be generated and stiffness values of each group were calculated at various displacements. Statistically significant results (P<.05) can be observed between groups.
Using a thin corneal flap allows for the detection of changes of the mechanical properties of corneal tissue induced by both large and small changes in the cross-linking procedure. This method is potentially able to detect changes in corneal mechanics induced with UVA-RF cross-linking routines with varying riboflavin concentration, UVA irradiance, total UVA energy, UVA application patterns, and ambient atmospheres.
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