Haidinger's brushes

noun plural

Hai·​ding·​er's brush·​es ˈhī-diŋ-ərz-ˈbrəsh-əz 

: a faint blue and yellow dumbbell-shaped image that is produced in the human eye by the selective absorption of polarized light by the yellow macular pigment of the fovea and can be used to detect polarized light without special equipment