Acoustic Micro-Tapping Optical Coherence Elastography to Quantify Corneal Collagen Cross-Linking: An Ex Vivo Human Study

Mitchell A Kirby; Ivan Pelivanov; Gabriel Regnault; John J Pitre; Ryan T Wallace; Matthew O'Donnell; Ruikang K Wang; Tueng T Shen

doi:10.1016/j.xops.2022.100257

Acoustic Micro-Tapping Optical Coherence Elastography to Quantify Corneal Collagen Cross-Linking: An Ex Vivo Human Study

Ophthalmol Sci. 2022 Nov 13;3(2):100257. doi: 10.1016/j.xops.2022.100257. eCollection 2023 Jun.

Authors

Mitchell A Kirby¹, Ivan Pelivanov¹, Gabriel Regnault¹, John J Pitre¹, Ryan T Wallace², Matthew O'Donnell¹, Ruikang K Wang^{1

3}, Tueng T Shen³

Affiliations

¹ Department of Bioengineering, University of Washington, Seattle, Washington.
² School of Medicine, University of Washington, Seattle, Washington.
³ Department of Ophthalmology, University of Washington, Seattle, Washington.

Abstract

Purpose: To evaluate changes in the anisotropic elastic properties of ex vivo human cornea treated with ultraviolet cross-linking (CXL) using noncontact acoustic micro-tapping optical coherence elastography (AμT-OCE).

Design: Acoustic micro-tapping OCE was performed on normal and CXL human donor cornea in an ex vivo laboratory study.

Subjects: Normal human donor cornea (n = 22) divided into 4 subgroups. All samples were stored in optisol.

Methods: Elastic properties (in-plane Young's, E, and out-of-plane, G, shear modulus) of normal and ultraviolet CXL-treated human corneas were quantified using noncontact AμT-OCE. A nearly incompressible transverse isotropic model was used to reconstruct moduli from AμT-OCE data. Independently, cornea elastic moduli were also measured with destructive mechanical tests (tensile extensometry and shear rheometry).

Main outcome measures: Corneal elastic moduli (in-plane Young's modulus, E, in-plane, μ, and out-of-plane, G, shear moduli) can be evaluated in both normal and CXL treated tissues, as well as monitored during the CXL procedure using noncontact AμT-OCE.

Results: Cross-linking induced a significant increase in both in-plane and out-of-plane elastic moduli in human cornea. The statistical mean in the paired study (presurgery and postsurgery, n = 7) of the in-plane Young's modulus, $E = 3 μ$ , increased from 19 MPa to 43 MPa, while the out-of-plane shear modulus, G, increased from 188 kPa to 673 kPa. Mechanical tests in a separate subgroup support CXL-induced cornea moduli changes and generally agree with noncontact AμT-OCE measurements.

Conclusions: The human cornea is a highly anisotropic material where in-plane mechanical properties are very different from those out-of-plane. Noncontact AμT-OCE can measure changes in the anisotropic elastic properties in human cornea as a result of ultraviolet CXL.

Keywords: AμT, acoustic micro-tapping; BSS, balanced saline solution; CXL, cross-linking; Cornea; Cross-linking; Elastic Anisotropy; IOP, intraocular pressure; NITI model; NITI, nearly incompressible transverse isotropy; OCE, optical coherence elastography; Optical Coherence Elastography; RF, riboflavin; UV, ultraviolet.

Abstract

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