Fig. 1: Brillouin measurements at different laser incidence angles detect tissue anisotropy.
From: Measuring mechanical anisotropy of the cornea with Brillouin microscopy
a Within each lamella, collagen fibers (f) are co-aligned within a gel matrix (m). We define a coordinate system (1–3) for each lamella in which the 1-direction is always aligned with the fibril axis. b The elastic modulus in the 1-direction C11 is different than the moduli orthogonal to the fibril axis, C22 and C33. By reducing the laser spot size, it is possible to resolve individual lamellae using Brillouin microscopy. When the laser spot size covers multiple lamellae, we measure a combined modulus. For the bulk stroma we define the z-direction as orthogonal to the cornea and the x−y plane as tangential. c Cut-away view through the stromal depth showing stacked lamellae. The cornea is mechanically anisotropic, meaning that the longitudinal moduli (Cii) have directional dependence. This can be probed using Brillouin microscopy with varying laser incidence angle θ.
