Shearing an initially isotropic Langmuir film by a rotating disk can lead to an optical anisotropy at the interface. This induced anisotropy is related to a local in-plane molecular alignment due to the shearing and was experimentally observed using a monolayer based on a liquid crystal polyacrylate. The variation of the anisotropy versus shearing was modelized and measured by Brewster angle microscopy. The results reveal that the optical property of such a monolayer is similar to that of a two dimensional nematic liquid crystal.