An optical device includes a frame supporting a lightguide, a microdisplay, and a field lens positioned therebetween that directs light from the microdisplay into a top surface of the lightguide. Four optical surfaces of the lightguide include: a curved surface where light from the microdisplay enters a top of the lightguide, curved eye-side and world-side surfaces providing total internal reflection, and a combiner surface. The eye-side surface is used twice. Once in total internal reflection, and a second time as a refractive surface when light is reflected from the combiner surface and is thereby refracted out of the lightguide and directed towards a user's eye. The field lens has a curved first surface oriented toward the microdisplay and a curved second surface oriented toward the top of the lightguide. The combiner surface combines ambient light from a world-side of the lightguide with light from the microdisplay.