IN A SERIES of articles published between 1844 and 1854, Wilhelm Karl von Haidinger1 described a phenomenon which became known as Haidinger's brushes (Haidingersche Lichtpolarisationsbüschel). This phenomenon can be seen if polarized light enters the eyes, or if one looks through a Nicol prism at a regular white background or, better still, against the blue sky.
An excellent picture of Haidinger's brushes can be found in Holm's2 article; this illustration is much better than Helmholtz' reproduction. These brushes consist of two rather bright spots, bordered by two hyperbols belonging together and appearing as bluish on a white background, and of somewhat darker brushes which are yellowish and fill the space between the bluish spots. Rotation of the Nicol prism causes the polarization plane to rotate also.
Haidinger's brushes have evoked the interest of many physiologists and ophthalmologists. Helmholtz,3 Dimmer,4 Fortin,5 Tschermak-Seysenegg6 and Gording7
GOLDSCHMIDT M. A NEW TEST FOR FUNCTION OF THE MACULA LUTEA. Arch Ophthalmol. 1950;44(1):129-135. doi:10.1001/archopht.1950.00910020132008