The phenomenon of glistenings, often appearing in intraocular lenses (IOLs) of patients after some time from the surgical operation, is potentially able to induce a poor quality of vision and, therefore, frustrate IOL implantation itself. In this paper, we combine optical microscopy with micro-Raman spectroscopy to get a deeper insight on the mechanism ruling, at microscopic scale, glistening formation. In particular, we have analyzed two types of IOLs, characterized by a different internal hydrophobicity but a similar polymer hydration coefficient. Raman imaging of single microvacuoles reveals that water creeps into the polymeric network, which traps water. Finally, applying the Principal Component Analysis (PCA) to Raman data, we provide information on the probable mechanism leading to water trapping in the two kinds of analyzed IOLs.