Quantifying the effects of UV-A/riboflavin crosslinking on the elastic anisotropy and hysteresis of the porcine cornea by noncontact optical coherence elastography

The collagen fibril orientation of the cornea can provide critical information about cornea tissue health because diseases such as keratoconus and therapeutic interventions such as UV-A/riboflavin corneal collagen crosslinking (CXL) can alter the ultrastructural arrangement of collagen fibrils. Here, we quantify the elastic anisotropy and hysteresis of in situ porcine corneas as a function of intraocular pressure (IOP) with noncontact optical coherence elastography. Moreover, the effects of UV-A riboflavin corneal collagen crosslinking on the elastic anisotropy and hysteresis were evaluated. The propagation of an air-pulse induced elastic wave was imaged at stepped meridional angles by a home built phasestabilized swept source OCE system. The stiffness of the cornea was translated from the velocity of the wave, and the elastic anisotropy was quantified by modifying the planar anisotropy coefficient. As the IOP increased, the stiffness of the corneas increased from ∼18 kPa at 15 mmHg IOP to ∼ 120 kPa at 30 mmHg IOP. While there was a measureable hysteresis, it was not significant. After CXL, the Young's modulus of the corneas significantly increased from ∼18 kPa to ∼44 kPa at 15 mmHg IOP. The mechanical anisotropy also increased significantly from ∼10 a.u. in the untreated corneas to ∼23 a.u. in the CXL treated corneas, 15 mmHg IOP. However, CXL did not change the elastic anisotropic orientation, and the mechanical anisotropic hysteresis was not significant after CXL.