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E. R. Mikula, H. Sun, K. Hollman, J. V. Jester, T. Juhasz; Measurement of Spatial Distribution of Corneal Elasticity With Acoustic Radiation Force Elasticity Microscope. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4630.
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The non-uniform structure of the cornea suggests an inhomogeneous spatial distribution of corneal elasticity. Using the newly developed non-invasive acoustic radiation force elastic microscopy (ARFEM) we show that the anterior cornea is more rigid than the underlying posterior stromal bed in cadaver porcine eyes.
Corneas from fresh porcine eyes (Sierra Medical, Whittier, CA) 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 in the anterior and posterior cornea. A confocal ultrasonic transducer applied 6.5 ms 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.
Bubble displacement was 18-25% greater in the posterior cornea relative to the anterior cornea. This indicates a larger Young’s modulus in the anterior cornea in the direction orthogonal to the corneal surface.
Our non-invasive ARFEM results indicate in cadaver porcine eyes that the anterior cornea is stiffer than the posterior cornea.
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