Disclosed is an optical film having an optical structure, such as a prism film or sheet, which is a constituent of a backlight unit. The optical film includes an optical structure layer having a plurality of optical structures, the surface of which is formed with irregularities, and the irregularities are formed on the surface of the light-collecting optical structure, such as a prism, to satisfy predetermined conditions, thus effectively realizing a light-diffusing function, thereby eliminating the need to additionally mount a diffusion film or a protection film. When a particle dispersion layer is further formed on the surface of a transparent substrate opposite the surface having the optical structure layer, damage due to friction to prism films or other sheets may be prevented during the layering of the prism films or transport, thus obviating the use of a plurality of optical films, consequently making it possible to economically manufacture a backlight unit with improved productivity.