Optical assembly (1, 100) intended to form a beam having a cutoff line, the optical assembly (1, 100) comprising: - a first optical part (2, 200) made of transparent material comprising: o light guides each comprising an entrance dioptre and an elementary exit; o a common exit located downstream of the elementary exits; o a first face extending between the elementary exits and the common exit, this first face being delimited downstream by a cutoff edge; - a reflective material (5; 50) distinct from the material of the first optical part (2; 200) and disposed opposite the first face of the first optical part (2; 200), the reflective material (5; 50) extending from the cutoff edge toward the elementary exits; the reflective material (5; 50) and the first optical part being arranged so as to be held together without a supplementary part and so that the reflective material (5; 50) is in direct contact with the cutoff edge; - the reflective material being formed by a reflection component (5; 50) separate from the first optical part (2; 200); - the reflection component (5; 50) having a first face, said first optical part (2; 200) comprising at least one pressing component (26, 29; 2600, 2900) arranged so that the first face of the reflection component (5; 50) is in direct contact with the cutoff edge, said first optical part (2; 200) and the pressing component (26, 29; 2600, 2900) being formed by a single one-piece part; characterized in that: - said first face of the reflection component (5; 50) has a downstream central portion, said direct contact being made with this downstream central portion and this downstream central portion being in direct contact with the first optical part (2; 200) only on the cutoff edge, the downstream central portion is delimited downstream by a downstream edge, the direct contact between the reflection component (5; 50) and the first optical part (2; 200) being formed by the direct contact of said downstream edge with the whole of the cutoff edge. - a first optical part (2, 200) made of transparent material comprising: o light guides each comprising an entrance dioptre and an elementary exit; o a common exit located downstream of the elementary exits; o a first face extending between the elementary exits and the common exit, this first face being delimited downstream by a cutoff edge; o light guides each comprising an entrance dioptre and an elementary exit; o a common exit located downstream of the elementary exits; o a first face extending between the elementary exits and the common exit, this first face being delimited downstream by a cutoff edge; - a reflective material (5; 50) distinct from the material of the first optical part (2; 200) and disposed opposite the first face of the first optical part (2; 200), the reflective material (5; 50) extending from the cutoff edge toward the elementary exits; the reflective material (5; 50) and the first optical part being arranged so as to be held together without a supplementary part and so that the reflective material (5; 50) is in direct contact with the cutoff edge; - the reflective material being formed by a reflection component (5; 50) separate from the first optical part (2; 200); - the reflection component (5; 50) having a first face, said first optical part (2; 200) comprising at least one pressing component (26, 29; 2600, 2900) arranged so that the first face of the reflection component (5; 50) is in direct contact with the cutoff edge, said first optical part (2; 200) and the pressing component (26, 29; 2600, 2900) being formed by a single one-piece part; characterized in that: - said first face of the reflection component (5; 50) has a downstream central portion, said direct contact being made with this downstream central portion and this downstream central portion being in direct contact with the first optical part (2; 200) only on the cutoff edge, the downstream central portion is delimited downstream by a downstream edge, the direct contact between the reflection component (5; 50) and the first optical part (2; 200) being formed by the direct contact of said downstream edge with the whole of the cutoff edge.