USING 3 DIFFERENT BIOMECHANICAL MEASUREMENT APPROACHES IN THE SAME EYE AFTER CXL EX VIVO: BRILLOUIN MICROSCOPY, HIGH-RESOLUTION OCT-ELASTOGRAPHY AND EXTENSOMETRY

Purpose: Keratoconus and other ectatic diseases are defined by reduced biomechanics. However, clinical ophthalmology generally relies on tomographical imaging of corneal curvature, because none of the current diagnostic approaches for corneal biomechanical measurements are considered precise or localized enough. Here, we compare, for the first time, the biomechanical impact of corneal cross-linking using 1) the Brillouin Optical Scanning System (BOSS), 2) Optical Coherence Elastography (OCE) and 3) classic stress-strain extensometry (as the benchmark) in the same eyes, ex vivo.

Setting: University of Zurich, CABMM; OPTIC team, Computer Vision Laboratory, ETH Zurich; ELZA Institute, Dietikon/Zurich, Switzerland

Methods: Porcine eyes were subjected to accelerated high-fluence corneal cross-linking, and then assessed biomechanically. Brillouin microscopy uses non-linear scattering of laser light to measure an optical frequency shift in the reflected light wavelength. High-resolution OCE uses pressure modulation and optical coherence imaging to obtain the axial strains. The biomechanical anaylsis was assessed by the three different approaches, respectively by (1) quantifying the Brillouin frequency shift, (2) computing the axial gradient of the induced displacement and (3) measuring the slope in the stress-strain curve after controlled load application.

Results: We will present results from a series of ex vivo measurments in porcine corneas.

Conclusions: We used two novel approaches, OCT-Elastography and Brillouin microscopy, to assess corneal biomechanical after corneal cross-linking in a localized manner, rather than measuring an overall corneal response. Such three-dimensional information on corneal biomechanics might open alleys to deepen our understanding of corneal changes observed in various clinical and surgical applications.