A method, apparatus, and computer program product for identifying features in a sample by analyzing Mueller matrices to calculate an average degree of polarization, a weighted average degree of polarization, a degree of polarization map, a degree of polarization surface. Also, a method, apparatus, and computer program product for identifying features in a sample by analyzing Mueller matrices to calculate depolarization relative to a retardance axis and/or a diattentuation axis, and to calculate a ratio of diattenuation to polarizance or ratios of row and column magnitudes. Also, a method for retinal polarimetry, including a non-depolarizing light tube configured for insertion into the eye.