 Pursuant to the Fresnel laws, the behavior and distribution of unguided oblique rays in the cylindrical geometry of the foveal blue cones produce an extrinsic dichroism.The size of the brush is consistent with the size of the macula (see graphic, above).It is thought that the macula's dichroism arises from some of its pigment molecules being arranged circularly; (the small proportion of circularly arranged molecules accounts for the faintness of the phenomenon.)