Said device applies in particular to in vivo diagnostic and prognostic assistance for physiopathological changes to biological tissues. It comprises a coherent light source (13) for emitting coherent light along a first direction (X), for the purpose of illuminating a biological tissue (16) in first and second areas thereof, the first area being sound and the second area liable to include changes, the tissue thus illuminated generating a speckle phenomenon, means (14) for observing the speckle field in a second direction (Y) and for acquiring the speckle, and means (18) for varying the angle between the first and second directions, in order to observe the speckle field at different angles, so as to acquire information about the tissue at various depths in this tissue, support and absorption means (20, 28) to maintain a constant distance between the surface of the tissue and the observation and acquisition means and to absorb possible movements of the tissue, electronic means (22) for processing the speckle figures obtained by means of the observation and acquisition means, said processing being carried out in particular by a fractal method, in order to compare the first and second areas, and electronic means (24) for analysing the processing of the figures, by statistical methods, making it possible to validate the comparison made between the first and second areas.