An optical film to visually reduce frame size of individual display units within a single large display includes four film portions connected to each other to form a rectangular frame of each individual display unit. Each film portion has strip-shaped micro-structures of triangular cross-section, and includes a bottom surface, a first side surface, and a second side surface. The bottom surfaces of the micro-structures are connected to each other. The first side surfaces and the second side surfaces are obliquely connected, the second side surface of one micro-structure being at the outermost side of each film portion. Angle θ1 between the first side and bottom surface of each micro-structure is less than angle θ2 between the first side surface and the second side surface and the sum of first and second angles θ1 and θ2 is less than 90°.