Noninvasive imaging of unstained living cells allows to study living specimens without altering them, and is a widely used technique in biotechnology for determining biological and biochemical roles of proteins. luorescence and contrast images are both used complementarily for better outcomes. However, segmentation of contrast images is particularly difficult due to the presence of lighting/shade-off artifacts, defocused scans, or overlapping. In this work, we make use of the optical properties intervening during the image formation process for cell segmentation. We propose the shear oriented polar snakes, an active contour model that implicitly involves phase information. Experimental results confirms the method suitability for cell images segmentation.