The present invention relates to an optical film having improved optical performance and to a backlight unit comprising the same. More particularly, the present invention relates to a microlens array (MLA) sheet which comprises a base unit and a lens unit formed on one side of the base unit, wherein the lens unit consists of a plurality of conical lenses. Existing hemispherical microlens array sheets have limitations in terms of improving luminance, and therefore cannot replace prism sheets in high luminance products. However, the microlens array sheet consisting of conical lenses of the present invention can improve both luminance and viewing angle characteristics.