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Kirill Larin, Manmohan Singh, Zhaolong Han, Srilatha Vantipalli, Salavat Aglyamov, Michael D Twa; Noncontact Quantitative Optical Coherence Elastography of the Cornea. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2440. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Various diseases, such as keratoconus, and therapeutic interventions, such as riboflavin corneal collagen crosslinking (CXL), can alter corneal biomechanical properties, resulting in changes of visual acuity. Hence, quantifying corneal biomechanical properties can provide critical information for detecting diseases, assessing corneal health and integrity, and evaluating the outcomes of therapeutic interventions. Here, we demonstrate optical coherence elastography (OCE) technique for noncontact quantifying corneal biomechanical properties.
Fresh porcine and rabbit whole eyes were used. In the porcine eyes, a focused micro air-pulse induced low-amplitude (≤ 10 μm) elastic waves, which were detected by OCE system. The OCE measurements were repeated at various intraocular pressures before and after traditional CXL procedure. The corneal viscoelasticity was quantified by using Rayleigh-Lamb wave model, which incorporated the corneal thickness and fluid-structure interface. In the rabbit eyes, OCE technique was used to evaluate the outcomes of spatially selective CXL at a fixed IOP of 15 mmHg. A central ~2 mm diameter region of the corneas was masked during CXL, and a grid of co-focused OCE measurements was made on a 4 mm by 4 mm region across the apex of the cornea after CXL. The low amplitude relaxation process of the displacement was fitted to a kinematic model to quantify the damped natural frequency (DNF), which is directly linked to Young’s modulus.
The CCT of the porcine samples decreased linearly as a function of IOP before and after CXL (P=0.028 and 0.005, respectively). The Young’s modulus also decreased linearly as a function of IOP before and after CXL (P=0.006 and 0.013, respectively). However, the shear viscosity did not change as a function of IOP before or after CXL (P=0.520 and 0.248, respectively). In the rabbit samples, the DNF clearly differentiated between the untreated and CXL-treated regions, with an increase in the mean DNF of ~68% (P<0.001) in all 4 samples.
CXL increased the stiffness of corneal tissue, but the Young’s modulus is also dependent on IOP. However, viscosity is not dependent on IOP and becomes more invariant as a function of IOP after CXL. Similarly, the spatially selective CXL procedure distinctly stiffened the unmasked region. Our results show that OCE is a powerful tool for quantitatively assessing corneal biomechanical properties completely noninvasively.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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