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The biomechanical properties of the cornea are critical factors which determine its health and subsequent visual acuity.
Keratoconus is a structural degeneration of the cornea which can diminish vision quality. Riboflavin/UV-A corneal
collagen cross-linking (UV-CXL) is an emerging treatment that increases the stiffness of the cornea and improves its
ability to resist further degeneration. While UV-CXL has shown great promise for effective therapy of the keratoconus,
there are concerns associated with the UV irradiation, such as keratocyte cytotoxicity. Rose-bengal/green light corneal
collagen cross-linking (RGX) has been proposed as an alternative to UV-CXL. Because of the high absorbance of the
rose-bengal dye at green wavelengths, the treatment time is significantly shorter than with UV-CXL. Moreover, because
green light is used in lieu of UV irradiation, there are no cytotoxic side-effects. In this study, noncontact optical
coherence elastography (OCE) was used to compare the outcomes of UV-CXL and RGX treatment in rabbit cornea.
Low-amplitude (micrometer scale) elastic waves were induced by a focused air-pulse loading system. The elastic wave
propagation was then imaged by a phase-stabilized swept source OCE (PhS-SSOCE) system. The changes in the
viscoelasticity of the corneas were quantified by a previously developed modified Rayleigh Lamb frequency model. The
depth-resolved micro-scale phase-velocity distribution in the cornea was used to reveal the depth-wise heterogeneity
before and after both cross-linking techniques. Our results show that UV-CXL and RGX increased the stiffness of the
corneas by ~54% and ~5% while reducing the viscosity by ~42% and ~17%, respectively. The depth-wise phase
velocities showed that UV-CXL affected the anterior ~1/3 of the corneas, while RGX only affected the anterior ~1/7 of
the corneas.
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