Lesion in autonomic system will affect both the sympthetic and parasympthetic systems : Pupil dilation occurs by sympatheticfibersinnervating pupillodilator muscle fibers. Pupil constriction is achieved by parasympathetic fibers. When there occurs a lesion in both the pathways, there will be no net effect, as there is no dilation or constriction, so the pupil will appear normal in size The pupils normal response to light is constriction, which is also absent here as the parasympathetic fibers responsible for constriction are also affected.