In situ Brillouin light scattering measurements with a spatial resolution of similar to 1 m have been carried out to study the elastic moduli of silica glass fibers in a single two-point bend experiment to nominal strains of 7% in both tensile and compressive regions. Such data are necessary in order to convert the failure strains obtained from two-point bend experiments into failure stress. For the first time, the neutral axis shift in a bent silica glass fiber was observed in our measurements, with more of the fiber deforming in compression than in tension, resulting from the nonlinear elastic behavior of silica glass. Understanding the neutral axis shift will improve the accuracy of strain and stress calculations in bent fibers. This study shows that an expression including a fifth-order term is required to capture both the minimum in compression and the maximum in tension in the strain-dependent Young's modulus of silica glass. A stress versus strain relation over a broad range of compressive and tensile strains was established for silica glass in this study, which will significantly improve our understanding of its deformation behavior.