An optical device, comprising: a light-transmitting substrate having at least two major surfaces (26, 27) and edges; optical means for coupling image light waves into said substrate by total internal reflection, the optical means having an active input aperture; means (4, 6) for producing the image light waves coupled by the optical means into the substrate by total internal reflection, wherein the means (4, 6) for producing the image light waves is located next to one of said two major surfaces (26, 27) acting as the input surface of the substrate and wherein the means (4, 6) for producing the image light waves comprises a display source and an imaging lens; and a plurality of partially reflecting surfaces (22, 22a, 22b, 22c) carried by the substrate, wherein the partially reflecting surfaces (22, 22a, 22b, 22c) are parallel to each other and are not parallel to any of the edges of the substrate; whereas at least one of the partially reflecting surfaces (22a, 22b, 22c) does not intersect with at least one of the two major surfaces (26, 27) and wherein the active input aperture of the optical means is large enough to be illuminated by the light waves from the display source, characterized in that points on a boundary line between an edge of the optical means and one of the two major surfaces of the substrate with which the optical means intersects are illuminated by two extreme rays (18a, 18b) from one of the light waves from the display source that enters the substrate from two different locations, one of the extreme rays illuminating the boundary line directly and the second of the extreme rays being first reflected by the optical means and then by the other one of the two major surfaces of the substrate before illuminating the boundary line. a light-transmitting substrate having at least two major surfaces (26, 27) and edges; optical means for coupling image light waves into said substrate by total internal reflection, the optical means having an active input aperture; means (4, 6) for producing the image light waves coupled by the optical means into the substrate by total internal reflection, wherein the means (4, 6) for producing the image light waves is located next to one of said two major surfaces (26, 27) acting as the input surface of the substrate and wherein the means (4, 6) for producing the image light waves comprises a display source and an imaging lens; and a plurality of partially reflecting surfaces (22, 22a, 22b, 22c) carried by the substrate, wherein the partially reflecting surfaces (22, 22a, 22b, 22c) are parallel to each other and are not parallel to any of the edges of the substrate; whereas at least one of the partially reflecting surfaces (22a, 22b, 22c) does not intersect with at least one of the two major surfaces (26, 27) and wherein the active input aperture of the optical means is large enough to be illuminated by the light waves from the display source, characterized in that points on a boundary line between an edge of the optical means and one of the two major surfaces of the substrate with which the optical means intersects are illuminated by two extreme rays (18a, 18b) from one of the light waves from the display source that enters the substrate from two different locations, one of the extreme rays illuminating the boundary line directly and the second of the extreme rays being first reflected by the optical means and then by the other one of the two major surfaces of the substrate before illuminating the boundary line.