UC Irvine

The human cornea is a complex, inhomogeneous layered structure which acts as our window to the world. The mechanical properties of the cornea, along with the underlying corneal microstructure help determine the shape of the corneal surface, and thus also determine visual acuity. Since the cornea provides nearly two thirds of the refractive power of the eye, even small alteration of the corneal surface can have significant impact on the quality of vision. Furthermore, understanding corneal mechanics is useful when considering refractive disorders in the cornea such as keratoconus, while also providing a better understanding of the corneal response to refractive surgery or collagen cross linking procedures.

To investigate corneal elastic properties we developed an acoustic radiation force elasticity microscope (ARFEM). ARFEM applies a low frequency, high intensity acoustic radiation force to axially displace a femtosecond laser generated micro-bubble, while using a high frequency, low intensity ultrasound to monitor the position of the micro-bubble within the cornea. The maximum displacement of the micro-bubble is inversely proportional to elastic modulus. We found that the overall stiffness of the human cornea varies considerably throughout its volume. The anterior cornea is significantly stiffer than the posterior in the central and middle cornea, with the trend reverses at the periphery near the limbus. We also evaluated the effects of non-linear optical cross-linking and demonstrated the ability of the procedure to stiffen the cornea.