Brillouin Optical Spectroscopy for In Vivo and Ex Vivo Assessment of Corneal Biomechanics.

Abstract

PURPOSE: Corneal ectasias, such as keratoconus, exhibit altered corneal shape, structure, and biomechanics. Patients would greatly benefit from volumetric, 3-dimensional, and regional measurements of corneal stiffness for early detection and post-treatment monitoring. Current methods use indirect measurements, confounded by intraocular pressure, corneal thickness, describing a global picture of the cornea, and fail to identify crucial early localized changes. We tested the Brillouin Optical Scanner System (BOSS), which uses the Brillouin principle for noncontact focal measurement of compressibility and corneal stiffness, expressed as the 3-dimensional Brillouin Longitudinal Modulus. METHODS: We measured compressibility/corneal stiffness in 3-month and 10-month-old New Zealand white rabbits (n = 2; male = 1; female = 1). Rabbits remained awake, calm, and nonsedated. We separately analyzed ex vivo porcine corneas using BOSS (n = 28) and strip extensiometry (n = 13). The BOSS parameters were optimized for both sets of analyses. RESULTS: The BOSS demonstrated precise measurements in in vivo rabbits and ex vivo porcine corneas with a <2% and <4% variation from the mean. All rabbit corneas (n = 4) showed an increase in Brillouin values, demonstrating an increase in corneal stiffness over 7 months, in vivo. CONCLUSIONS: The BOSS is capable of precise measurements and detecting subtle changes in corneal stiffness in the rabbits. The high precision and accuracy of biomechanical measurements in nonsedated rabbits will enable a reduction in preclinical animal numbers, especially for time course studies. Importantly, the ability of the BOSS to provide spatial biomechanical measurements makes it a valuable tool for early detection of asymmetric corneal ectasias and keratoconus.