the lens is made by injection molding in a mold through the injection of molten plastic material in at least three injection shots using a multistep process . it includes a first outer lens part , a second outer lens part and a lens core part forming an interior of the lens . the lens core part is embedded between the first and second outer lens parts . the lens core part is divided into at least two subparts separated at least partially by at least one elongated slot extending across the lens core part between the first and second surfaces of the lens core part . the slot or slots made through the lens core part are filled and fused with the plastic material of the first outer lens part .