Perception of Haidinger's Brushes and Macular Degeneration

Haidinger's brushes are an entoptical effect of the human visual system which enables us to detect polarized light. The mineralogist Wilhelm Haidinger (1844) discovered the effect and Helmholtz (1866) related the perception of the brushes to the concentric alignment of the dichroic pigment molecules around the fovea, which is called macula. The macula acts essentially like a radial polarizer. In addition, the perception of the brushes varies individually with the birefringence of the cornea. In our experimental setup we simulated various phase shifts and orientations of the cornea and recorded the brush pattern as it is generated by a radial polarizer. We modeled the transmission of the light through this system and were able to quantify the influence of the cornea on the pattern of Haidinger's brushes. We also calculated the light transmission through a system where the macula polarizes only partially. The brush pattern forming in this case may indicate macular degeneration.