Biomechanical Properties of Human Corneas Following Low- and High-Intensity Collagen Cross-Linking Determined With Scanning Acoustic Microscopy

PURPOSE. To assess and compare changes in the biomechanical properties of the cornea following different corneal collagen cross-linking protocols using scanning acoustic microscopy (SAM). METHODS. Ten donor human corneal pairs were divided into two groups consisting of five corneal pairs in each group. In group A, five corneas were treated with low-fluence (370 nm, 3 mW/cm(2)) cross-linking (CXL) for 30 minutes. In group B, five corneas were treated with high-fluence (370 nm, 9 mW/cm2) CXL for 10 minutes. The contralateral control corneas in both groups had similar treatment but without ultraviolet A. The biomechanical properties of all corneas were tested using SAM. RESULTS. In group A, the mean speed of sound in the treated corneas was 1677.38 +/- 10.70 ms(-1) anteriorly and 1603.90 +/- 9.82 ms(-1) posteriorly, while it was 1595.23 +/- 9.66 ms(-1) anteriorly and 1577.13 +/- 8.16 ms(-1) posteriorly in the control corneas. In group B, the mean speed of sound of the treated corneas was 1665.06 +/- 9.54 ms(-1) anteriorly and 1589.89 +/- 9.73 ms(-1) posteriorly, while it was 1583.55 +/- 8.22 ms(-1) anteriorly and 1565.46 +/- 8.13 ms(-1) posteriorly in the untreated control corneas. The increase in stiffness between the crosslinked and control corneas in both groups was by a factor of 1.051X. CONCLUSIONS. SAM successfully detected changes in the corneal stiffness after application of collagen cross-linking. A higher speed-of-sound value was found in the treated corneas when compared with the controls. No significant difference was found in corneal stiffness between the corneas cross-linked with low-and high-intensity protocols.