Initial results of study a lateral stress, static and dynamic, on a light propagation in a high birefringent fiber are presented. A permanent birefringence in optical fiber arises due to large thermal stress in the core. Ambient parameters like temperature and hydrostatic pressure influence the stress anisotropy and thus the light propagation. The parameters can be assumed as uniform and the optical response does not depend on the position of the fiber birefringent axes. For a stress (lateral pressure) the optical response of a fiber reveals an azimuth dependence on mutual direction of an exerted pressure and birefringent axes. With dynamic perturbation, even slowly varying, some additional effects like strain can not be avoided. The effective optical response is composed and strongly depends on the direction of stress.