Embodiments test a subject's vision. A polarization arrangement polarizes incident light and rotates an angle of polarization applied to the incident light about an axis substantially collinear with a path of the light. An optical component directs light onto the polarization arrangement and produces light having a selected degree of polarization and having a rotating angle of polarization for observation by the subject The subject may be able to observe the visual phenomenon known as Haidinger's brushes and due to the rotation of the angle of polarization the eye's tendency to adapt away the phenomenon is counteracted, so that the effect persists and a more reliable testing of the subject can be carried out. Testing the subject's ability to perceive the phenomenon at multiple selectable degrees of polarization enables an assessment of the subject's eyes, and an estimate of macular pigment optical density and susceptibility to age-related macular degeneration.