The glass beads are translucent objects that serve as a pattern to characterize different techniques for measuring phase object. These microspheres are of great importance in assessing metrological techniques, both industrial as medical and scientific level, in the measurement of refractive index. This paper shows the results acquired by using a technique that combines both Digital Holographic Microscopy in transmission and the tomographic reconstruction technique, applying inverse Radon transform. As input were taken the difference phase maps obtained from the registration procedure and holographic reconstruction. The application of this technique allows obtaining 3D maps of the refractive index of glass spheres with diameters of about 200 micrometers.