Figure 1.

Relationships between mechanical forces in the cornea and various mechanical testing methods. Mechanical forces in corneal tissue govern focusing power in (a) healthy and (b) pathological tissue (e.g. keratoconus). (c) Elastic shear waves generated in the cornea with a transient force are tracked using optical coherence tomography to determine corneal mechanical properties without contact. (d) Summary of biomechanical test methods and corneal Young’s and shear moduli from the literature. Reported moduli vary by up to four orders of magnitude depending on the loading technique and test configuration, suggesting that isotropic models cannot accurately describe corneal mechanics. In particular, tensile and inflation tests generally agree, as do shear and transient tests. Values listed are for fresh samples (within 2 weeks), and best effort was taken to report moduli in the low-strain/preload region where they generally are near their lowest value.