Volumetric distribution of a micromechanical parameter of a biological tissue, such as viscoelastic parameter or tissue stiffness, is determined, with microscopic resolution, from optical data representing light scattered by sequential layers of the tissue and, optionally, displayed to visualization. A particular layer of the tissue is defined through coherence-gating of light received at the optical detector. Coherence-gating is achieved with the use of an interferometer the sample arm of which contains the tissue, illuminated with defocused light, and an optical length of a reference arm of which is repeatedly adjusted, within a coherence length of used light, to ensure that each of the sequential optical interferograms represents light scattered only by a particular tissue layer a position of which is re-defined through the tissue via such adjustment.