Haidinger's brushes and predominant orientation of collagen in corneal stroma.

Abstract

WHEN a source of bluish light, such as the sky, is viewed through Polaroid glass or other polarising material, a characteristic figure known as Haidinger's brushes is fleetingly seen at the fixation point by most observers. The ‘brushes’ are shaped like an hourglass, yellow and darker than the surround, and are orientated with their long axis at right angles to the transmission plane of the Polaroid. On either side of the brushes are light blue areas which are brighter than the surround: by some observers they are seen more clearly than the brushes themselves. If the polaroid is rotated, the brushes rotate with it in the same direction, and this manoeuvre prevents the figure from fading.