An eye tracking system comprising: a display panel (128, 1510); and a light guide (122, 301, 407, 501, 601, 801 901, 1101) configured to be disposed between a user eye and the display panel, the light guide comprising a transparent body having: a first surface, a second surface opposite the first surface, and a third surface between the first surface and the second surface such that the third surface connects the first surface to the second surface; the first surface composed of a substantially planar surface; and the second surface comprising a combiner region (115, 1102) having a plurality of facets (114, 313, 401, 512, 612, 812, 912, 1112) arranged along a plane having a non-zero angle relative to the first surface and configured to reflect light incident on a corresponding region of the first surface internally through the body toward the third surface, characterised in that the display panel is positioned beyond the second surface of the light guide and oriented toward the user eye, the display panel configured to provide electronic images to the user eye, and wherein visible light from the display panel passes through the combiner region. a display panel (128, 1510); and a light guide (122, 301, 407, 501, 601, 801 901, 1101) configured to be disposed between a user eye and the display panel, the light guide comprising a transparent body having: a first surface, a second surface opposite the first surface, and a third surface between the first surface and the second surface such that the third surface connects the first surface to the second surface; the first surface composed of a substantially planar surface; and the second surface comprising a combiner region (115, 1102) having a plurality of facets (114, 313, 401, 512, 612, 812, 912, 1112) arranged along a plane having a non-zero angle relative to the first surface and configured to reflect light incident on a corresponding region of the first surface internally through the body toward the third surface, characterised in that the display panel is positioned beyond the second surface of the light guide and oriented toward the user eye, the display panel configured to provide electronic images to the user eye, and wherein visible light from the display panel passes through the combiner region. a first surface, a second surface opposite the first surface, and a third surface between the first surface and the second surface such that the third surface connects the first surface to the second surface; the first surface composed of a substantially planar surface; and the second surface comprising a combiner region (115, 1102) having a plurality of facets (114, 313, 401, 512, 612, 812, 912, 1112) arranged along a plane having a non-zero angle relative to the first surface and configured to reflect light incident on a corresponding region of the first surface internally through the body toward the third surface, characterised in that the display panel is positioned beyond the second surface of the light guide and oriented toward the user eye, the display panel configured to provide electronic images to the user eye, and wherein visible light from the display panel passes through the combiner region.