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Eric R. Mikula, James Jester, Tibor Juhasz; Measurement of Varying Elasticity Between Central and Peripheral Human Cornea With Acoustic Radiation Force Elasticity Microscope. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1524.
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The non-homogeneous organization of collagen across the cornea suggests a unique distribution of elastic moduli. Specifically, a difference in elasticity is expected between the central and peripheral cornea due to underlying structural differences. Using acoustic radiation force elastic microscopy (ARFEM), we measure the distribution of elastic properties across the cornea, both radially and axially, with the goal of constructing a cross-sectional map of elasticity.
Corneas from human cadaver eyes (San Diego Eye Bank, San Diego California) were excised from the globe leaving a 2 mm scleral rim intact. The corneal samples were suspended in collagen gelatin (10% w/w) within a water tank filled with deionized, degassed water. The water tank was attached to a 3-D mechanical stage allowing for precise control of cavitation bubble placement within the cornea. Femtosecond laser pulses induced optical breakdown and produced cavitation at points across the cornea. A confocal ultrasonic transducer applied a 2ms train of 200µs acoustic radiation force-chirp bursts to the bubble at 1.5 MHz while monitoring bubble position using pulse-echoes at 20 MHz. A cross-correlation method was used to calculate bubble displacements. Maximum bubble displacements are inversely proportional to the Young’s modulus.
Initial results indicate that the central cornea in the human eye is stiffer than the peripheral cornea in the direction orthogonal to the corneal surface.
Our non-invasive ARFEM results show the central cornea has a higher elastic modulus than the peripheral cornea and that elasticity varies throughout the cornea.
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