An optical fiber having a cladding region surrounding a core region having an elongate core hole, the inner or outer surface of the core hole having a surface roughness with a spatial period equal to or less than 5 μm by a spectral power below 0.0017 nm2μm−1. A method of making an optical fiber including a cladding region having an arrangement of elongate cladding holes in a matrix material, surrounding an elongate core region having an elongate core hole, the method including the step of increasing the surface tension of the matrix material prior to or during the step of heating and drawing the fiber.