Polarized light microscopy of weakly birefringent biological specimens

Summary A simple, but little known technique for producing marked colour contrast in images of weakly birefringent biological samples obtained with a polarized light microscope is investigated. The technique involves inserting a full wave plate at a small angle of horizontal rotation with respect to the analyser or polarizer, rather than at the conventional angle of 45° commonly employed in the field of mineralogy for examining strongly birefringent specimens. Inserting the full wave plate at a small angle (typically less than 10°) enhances the contrast between regions of tissue having different optical path differences and, in particular, different orientations of optic axes; improving the detection of structures of interest with the polarized light microscope.